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Papers - Ohmura, Ryo

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Hydrate-based continuous hydrogen gas separation from mixing gas containing carbon dioxide with cyclopentanone

Kamiya L., Kasai R., Takeya S., Ohmura R.

International Journal of Hydrogen Energy 121 111 - 117 2025.04

ISSN 03603199

Clathrate-hydrate-based H2 separation is superior to conventional separation methods in terms of energy consumption, but the criteria for selecting promoters that facilitate stable hydrate formation and gas separation are unclear. We conducted continuous and batch separation experiments in a CO2 + H2 + cyclopentanone (CP-one) system and powder X-ray diffraction (PXRD) measurements of the hydrate formed in this system. While the mole fraction of H2 in the gas phase increased from 0.60 to 0.90 in continuous separation, CO2 in the hydrate phase remained at 0.90. PXRD measurements revealed that CO2 + H2 + cyclopentanone hydrate possesses the structure II hydrate, suggesting CO2 and CP-one encapsulation in small and large cages of hydrate. Compared to previous studies using tetrahydropyran and cyclopentane as guest compounds, CP-one with high water solubility facilitated kinetics of the hydrate, encapsulation of CO2 in the hydrate and more stable separation. This study would provide a comprehensive understanding of selecting guest compounds for hydrate-based separation.

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Interfacial tension between water and pentane saturated with methane

Yamashita T., Iwai T., Alavi S., Ohmura R.

Colloids and Surfaces A: Physicochemical and Engineering Aspects 710 2025.04

ISSN 09277757

The plugging of natural gas pipelines caused by hydrate formation has been recognized as a problem in the oil and gas industry for approximately 90 years. Interfacial tension is an important physical property to understand the dynamics of multiphase flow, namely, natural gas, condensate, and water, inside the pipelines. This paper describes our measurements of the interfacial tension between water and pentane saturated with methane as a model for the fluids in the pipelines transporting gas and condensate. The measurements were conducted by the pendant drop method in the temperature range between 278.2 K and 293.2 K, and the methane pressure range between 1.1 MPa and 13.7 MPa. The uncertainty of the measurements is typically below 1.5 mN∙m−1. The interfacial tension decreased with increasing temperature at 2 MPa. As for the pressure dependence at 288.2 K, with increasing pressure, the interfacial tension decreased from 49.12 mN∙m−1 at 1.1 MPa to 47.64 mN∙m−1 at 4.0 MPa. The interfacial tension remained roughly constant until 8.7 MPa with the value being 48.02 mN∙m−1 and then increased to 59.81 mN∙m−1 at 12.9 MPa. The decrease of the interfacial tension between 1.1 MPa and 4.0 MPa could be attributed to the increase of the methane molecule adsorption at the interface. In the pressure range between 4.0 MPa and 8.7 MPa, it is likely that the methane adsorption at the water – pentane interface became saturated. The increase of the interfacial tension above 8.7 MPa is a novel phenomenon which requires further investigation.

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Demonstration of a Practical Cooling Storage System for Lithium-Ion Batteries with Trimethylolethane (TME) Hydrate for EV

Kamiya L., Koyama R., Arai Y., Ohmura R.

Energies 18 ( 6 ) 2025.03

Lithium-ion batteries are required to equip the cooling system for high power performance, quick charge, and safety. Trimethylolethane (TME) hydrate is known as phase change material (PCM), a cooling medium that offers large dissociation heat and 30 °C form/dissociation temperature under atmospheric pressure. This study demonstrates the design of a practical cooling system with TME hydrate. This cooling method involves cooling outdoor air through water contact, exchanging heat between the cooled outdoor air and the aqueous solution of TME hydrate, exchanging heat from the resulting TME hydrate with a refrigerant, and finally supplying the processed refrigerant to the cooling LIB. Koyama et al. conducted a study on the physical properties of TME hydrate. They measured equilibrium temperatures and dissociation heats of TME mass fractions from 0.20 to 0.80. Their findings revealed that at a mass fraction of 0.60, the system reached its highest equilibrium temperature of 29.6 °C, and the dissociation heat peaked at 190.1 kJ/kg. This cooling system employed TME hydrate. These results underscore the potential of TME hydrates in energy-efficient cooling systems and demonstrate that they are suitable for lithium-ion battery cooling systems.

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Phase Equilibrium of CO<inf>2</inf> Hydrate with Rubidium Chloride Aqueous Solution

Kasai R., Kamiya L., Ohmura R.

Separations 12 ( 1 ) 2025.01

Salt lakes are a rich source of metals used in various fields. Rubidium is found in small amounts in salt lakes, but extraction technology on an industrial scale has not been developed completely. Clathrate hydrates are crystalline compounds formed by the encapsulation of guest molecules in cage-like structures made of water molecules. One of the most important properties for engineering practices of hydrate-based technologies is the comprehension of the phase equilibrium conditions. Phase equilibrium conditions of CO2 hydrate in rubidium chloride aqueous solution with mass fractions of 0.05, 0.10, 0.15 and 0.20 were experimentally investigated in the pressure range from 1.27 MPa to 3.53 MPa, and the temperature was from 268.7 K to 280.6 K. The measured equilibrium temperature in this study decreased roughly in proportion to the concentration of the RbCl solution from the pure water system. This depression is due to the lowering of the chemical potential of water in the liquid phase by the dissolution of RbCl. Experimental results compared with other salt solution + CO2 hydrate systems showed that the equilibrium temperatures decreased to a similar degree for similar mole fractions.

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Eutectic conditions of carbon dioxide clathrate hydrate and sodium Chloride: Implications for zero liquid discharge seawater desalination

Gibo A., Nakao S., Ohmura R., Yasuda K.

Journal of Industrial and Engineering Chemistry 2025

ISSN 1226086X

The eutectic temperature, pressure, and concentration conditions of carbon dioxide clathrate hydrate and sodium chloride dihydrate were measured to advance clathrate hydrate-based seawater desalination and salt production technology that enables seawater desalination through zero liquid discharge. The measured eutectic conditions were within the temperature range of 256.2 K ≤ Teu ≤ 263.5 K, the pressure range of 0.91 MPa ≤ peu ≤ 2.70 MPa, and the concentration range, expressed as the mass fraction of sodium chloride, of 0.235 ≤ wm,eu ≤ 0.242. These eutectic conditions correspond to the four-phase equilibrium of a saturated sodium chloride aqueous solution, carbon dioxide clathrate hydrate, carbon dioxide gas, and sodium chloride dihydrate, as well as the five-phase equilibrium of a saturated sodium chloride aqueous solution, carbon dioxide clathrate hydrate, carbon dioxide gas, liquid carbon dioxide, and sodium chloride dihydrate. Based on the measured eutectic conditions, implications for implementing clathrate hydrate-based seawater desalination and salt production were presented, including a conceptual design for a methodology involving reverse osmosis, multi-stage clathrate hydrate-based seawater desalination, and clathrate hydrate-based seawater desalination and salt production.

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Effect of sucrose fatty acid ester on crystal growth of carbon dioxide hydrate in aqueous fructose solution

Nagayama S., Maruyama M., Tokunaga R., Alavi S., Ishihara K., Kawamoto M., Ohmura R.

Journal of Molecular Liquids 411 2024.10

ISSN 01677322

CO2 hydrate is a remarkable candidate for novel solid carbonated foods because of its large gas capacity. This paper reports the effect of surfactants, essential additives in food production, on hydrate crystal growth by visually observing the CO2 hydrate crystal growth in aqueous fructose + sucrose fatty acid ester solution + gaseous CO2 system. Under all thermodynamic conditions, the surfactants affected the crystal growth of CO2 hydrates at liquid/gas interface, while not influencing growth in the liquid bulk phase. Porous hydrate crystals were formed at the liquid/CO2 interface and grew continuously along the reactor wall. The hydrate crystal morphology in liquid bulk phase was not affected by surfactants, changing from polyhedral and polygonal to dendritic shapes as temperature decreased. Discussion is provided on how the observation results can be specifically applied to intensification of hydrate formation process design and evaluation of hydrated food texture.

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Phase equilibria and crystallographic structure of clathrate hydrate formed with carbon dioxide and cyclohexanone

Kamiya L., Kasai R., Takeya S., Ohmura R.

Fluid Phase Equilibria 585 2024.10

ISSN 03783812

This paper reports the phase equilibrium and crystallographic data of the hydrate formed in the CO2 + cyclohexanone + water system. We measured the phase equilibrium condition and conducted the powder X-ray diffraction measurements. The formation of the structure II hydrate in the system of CO2 + cyclohexanone + water was observed at the temperature from 270.0 K to 275.6 K, under the pressure from 0.62 MPa to 1.70 MPa. At 270.0 K – 275.6 K and 0.62 MPa – 1.70 MPa, the structure II hydrate formed, and the phase equilibrium condition alleviated in the system of CO2 + cyclohexanone + water, while the hydrate formed at 276.5 K - 280.7 K and 2.02 MPa – 3.33 MPa, displayed structure I and cyclohexanone acted as an inhibitor. Equilibrium conditions were measured using the isochoric method, revealing different p-T slopes at high and low temperatures. The high-temperature slope closely resembled that of structure I CO2 hydrate reported previously. We continuously monitored temperature and pressure during the structural phase transition, resulting in a slope change. To directly determine the hydrate structure, PXRD measurements were conducted on two samples: one from the high-temperature side and the other from the low-temperature side. The sample from the high-temperature side exhibited structure I with a lattice constant of 11.8749 (9) Å at 153 K, while the low-temperature sample displayed structure II with a lattice constant of 17.443(1) Å at 153 K.

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Thermophysical Properties of Clathrate Hydrates with Various Guests for Novel Technologies: A Review

Yasuda K., Ohmura R.

International Journal of Thermophysics 45 ( 10 ) 2024.10

ISSN 0195928X

Thermophysical properties relevant to clathrate hydrate-based technologies were reviewed. Clathrate hydrates are solids composed of water and guests. The clathrate hydrate-based technologies considered in this study were as follows: carbon capture, utilization, and sequestration; natural gas storage and transportation; ozone storage and transportation; carbon dioxide clathrate hydrate as food; desalination and salt production; separation of tritiated water; cold thermal energy storage; and heat pumps and heat engines. The review was based on the experimentally measured data. The reviewed thermophysical properties were phase equilibrium conditions, formation/decomposition enthalpy, heat capacity, thermal conductivity, interfacial tension, and density. The phase equilibrium conditions determine the operating conditions for the clathrate hydrate-based technologies. The formation/decomposition enthalpy, heat capacity, and thermal conductivity relate to the thermal energy exchange during hydrate formation/decomposition. The interfacial tension is a key parameter when considering the multiphase flow composed of water and guests. The density influences the behavior of clathrate hydrates within the reactor. The relevance between these properties and the clathrate hydrate-based technologies was discussed. The methods correlating the phase equilibrium conditions were also compared in terms of applicability and usefulness. It was revealed that the suitability of the model, which is based on the Clausius–Clapeyron equation or statistical thermodynamic modeling, depends on the purpose of the correlation. Future perspectives of the thermophysical properties of clathrate hydrates were also discussed.

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Surface tension of aqueous solutions of large organic salts: Tetrabutylammonium acetate solutions

Yamashita T., Shigehara S., Alavi S., Ohmura R.

Journal of Molecular Liquids 404 2024.06

ISSN 01677322

Aqueous solutions of simple ionic salts such as NaCl and NaBr have higher surface tensions compared to that of pure water and the surface tension of the solution increases with the increasing concentration of the salt. In contrast, the aqueous solutions of the ion sodium acetate (NaAc), which has an anion with both hydrophilic and hydrophobic parts, have a surface tension less than that of pure water, with the surface tension decreasing with salt concentration. The presence of large cations in the salt may change these trends. In this work, the interfacial tension of aqueous solutions of the organic ionic salt tetrabutylammonium acetate (TBAAc) is measured and compared with that of tetrabutylammonium bromide (TBAB). The surface tension of TBAAc aqueous solutions with mole fractions ranging from 0.00417 to 0.04191 were measured for temperatures ranging from 288.2 to 308.2 K and compared with the surface tension of TBAB solutions at similar concentrations. The experimental results showed that the interfacial tensions of TBAAc and TBAB aqueous solutions decreased with increasing concentration, leveling at around 0.04 mol fraction. At each concentration, the interfacial tensions of the TBAAc solutions were larger than those of the TBAB solutions. For the TBAAc and TBAB solutions, the surface excess concentrations of the salts in the solutions are calculated. The impact of these results structures and properties of these solutions are discussed.

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Crystal Growth of Clathrate Hydrate Formed with Carbon Dioxide and Deuterium Oxide: Implications for Hydrate-based Tritium Separation

Maruyama M., Dogi K., Ohmura R.

Energy and Fuels 38 ( 7 ) 6215 - 6222 2024.04

ISSN 08870624

Tritium separation technology is a key method for treating contaminated water from nuclear power plants. Recently, a novel tritium separation method using deuterium oxide (D2O)-based clathrate hydrate has attracted attention because it can reduce the tritium concentration in contaminated water from 4.77 × 105 Bq/kg to 1.55 × 103 Bq/kg. In this hydrate-based tritium separation method, tritium is concentrated on the surface of a D2O-based hydrate substrate. The mechanistic characteristics and formation kinetics of D2O-based hydrates need to be clarified to develop an efficient process for substrate formation. This study contributes to the process design by revealing the crystal growth of the CO2 + D2O hydrate. The crystal growth behavior of the hydrate formed in the CO2 + D2O system was experimentally observed under different subcooling temperatures (ΔTsub) at 3.0 MPa. At all ΔTsub, hydrate crystals were formed at the gas-liquid interface and extended along the interface. After the interface was covered, hydrate crystals grew in the liquid phase. The variation in the morphology of CO2 + D2O hydrate depended on ΔTsub. At ΔTsub = 1.6 K, polygonal crystals with side lengths of 0.2-0.6 mm were formed. At ΔTsub = 2.7 K, columnar crystals with a length of 1-2 mm were formed. At ΔTsub ≥ 3.3 K, dendritic crystals were formed. With an increase in ΔTsub, the size of the dendritic branches increased. The crystal growth dynamics and morphological tendency of the CO2 + D2O hydrate were comparable to those of the CO2 + H2O hydrate at fixed ΔTsub. Detailed theoretical discussions on the obtained results of surface kinetics, mass transfer, and heat transfer during hydrate formation from H2O and D2O were provided, considering the chemical potential, viscosity, and heat transfer of the liquids.

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Characterization of clathrate hydrates with CO<inf>2</inf> + 1-propanol or 2-propanol: Implications for flow assurance, refrigeration, carbon capture, and skincare applications

Maruyama M., Takeya S., Yoneyama A., Ishikawa T., Misawa T., Nagayama S., Alavi S., Ohmura R.

Journal of Industrial and Engineering Chemistry 131 305 - 314 2024.03

ISSN 1226086X

There has been growing interest in the use of hydrate-based technology for energy and environmental applications; however, structural characterization of some hydrate phases relevant to these applications has not been dealt with sufficiently in previous studies. This paper reports crystallographic characterization of hydrates formed in [CO2 + 1-propanol (propan-1-ol) + water] and [CO2 + 2-propanol (propan-2-ol) + water] systems with powder X-ray diffraction (PXRD) and X-ray computed tomography (CT) measurements. It was revealed that structure I CO2 hydrate and a non-crystalline phase involving 1-propanol are formed in CO2 + 1-propanol system. As for CO2 + 2-propanol system, crystalline structure of the formed hydrate differs depending on thermodynamic conditions; at 3.3 MPa, 274 K and at 2.2 MPa, 263 K, sI CO2 hydrate was formed, whereas at lower pressure and temperature, i.e., 0.5 MPa and 255 K, a new tetragonal structure outside the canonical hydrates was identified. Implications of using 1-propanol as a thermodynamic inhibitor and kinetic promoter of hydrate formation are discussed, which opens some possibilities into petroleum exploration/production applications and the development of hydrate-based refrigeration systems. The structural identification of tetragonal (sII′) CO2 + 2-propanol hydrate sheds new light on developing hydrate-based CCS process and novel skin care products.

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Zero-point energy effects on the stability of water clusters: Implications on the uptake of hydrogen isotope substituted water on ice and clathrate hydrate phases

Ohmura R., Alavi S.

AIP Advances 14 ( 3 ) 2024.03

To study the effect of hydrogen isotope substitution on the uptake of water during formation of clathrate hydrates, the harmonic intermolecular librational modes of selected water clusters (X2O)n with n = 2-6 and hydrogen isotopes X = H, D, and T are studied. The effects of the quantum mechanical zero-point energy (ZPE) in each cluster on the binding energies of the H2O, D2O, and T2O clusters are determined, with ZPE leading to the smallest binding energies in the H2O clusters and the largest binding energies in the T2O clusters. Corrections for anharmonicity of the librational modes are considered, and these bring the frequency ranges of the calculated intermolecular librational modes in the clusters to the experimental ranges of the librational modes in the infrared spectra of H2O and D2O solid ice and clathrate hydrate phases, and liquid H2O water. These calculations show the expected ranges of the binding energy of tritiated water onto a solid ice and clathrate hydrate surface and can help quantify the isotopic enrichment on a growing clathrate hydrate phase from the solution.

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Fiery ice: An overview of methane hydrate combustion

Dunn-Rankin D., Chien Y.C., Ueda T., Ohmura R.

Progress in Energy and Combustion Science 101 2024.03

ISSN 03601285

This article describes the combustion behavior of combustible gases as they are released from the clathrate cages of a hydrate. Gas hydrates (clathrates) are ice-like crystalline solids that encapsulate guest gas molecules. It has become known that a significant methane storehouse is in the form of methane hydrates on the sea floor and in the arctic permafrost. There is great interest in this large fuel storehouse, particularly how to extract the methane from the clathrates. One of the unique features of methane clathrate is that it is flammable, despite being 85% water – fiery ice. While methane clathrates are the most prevalent in nature, other combustible gas hydrates (notably, propane and hydrogen) also have potential energy technology implications. In addition, carbon-dioxide hydrates have been proposed as a potential post-combustion greenhouse gas sequestration strategy, and there is a wide range of separation technologies and thermal management that take advantage of the unique thermodynamic and kinetic features of hydrate formation. To better understand the important implications of direct utilization of fuel clathrates and the related potential environmental consequences of CO2 hydrates, we describe the state-of-the-art knowledge regarding the formation and structure of gas hydrates, and the combustion behavior of flammable gas hydrates. The combustion studies involve determining the rate of ice melt and water evaporation during the hydrate burn, as well as the interesting phenomenon of self-healing, where the hydrates stop burning by forming an ice sheet on their surface. Experimental results are used to estimate the heat transfer from the flame into the hydrate and to calculate the amount of energy released to sustain the flame. This article provides the reader with a comprehensive understanding of the basics and the subtleties of hydrates and their combustion, thereby explaining the true meaning of fiery ice.

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Phase equilibrium conditions in carbon dioxide + cyclopentane double clathrate hydrate forming system coexisting with sodium chloride aqueous solution

Mekaru K., Miyagi T., Mishima A., Uehara I., Ohmura R., Yasuda K.

Journal of Chemical Thermodynamics 189 2024.02

ISSN 00219614

The four-phase equilibrium conditions were measured in carbon dioxide + cyclopentane double clathrate hydrate forming systems coexisting with either sodium chloride aqueous solution or pure water as a technological basis for developing seawater desalination technology utilizing clathrate hydrate formation and decomposition. The equilibrated phases included sodium chloride aqueous solution or pure water, carbon dioxide + cyclopentane double clathrate hydrate, liquid cyclopentane, and carbon dioxide gas. The experiments were performed using the batch isochoric procedure. Three different concentrations of sodium chloride in the aqueous solution were tested: 0.035, 0.070, or 0.105 in mass fraction. Pressures ranged from 0.385 MPa to 2.488 MPa. The results were compared with the equilibrium conditions for carbon dioxide and cyclopentane simple clathrate hydrate forming systems. The comparison revealed that the double clathrate hydrate is more thermodynamically stable than the simple clathrate hydrates, under a given sodium chloride concentration in the aqueous solution.

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Phase Equilibrium Conditions and Crystal Structure of Binary Hydrates Formed with 1-Methylpiperidine

Yamamoto K., Misawa T., Ito H., Takeya S., Alavi S., Ohmura R.

Journal of Physical Chemistry C 128 ( 3 ) 1312 - 1322 2024.01

ISSN 19327447

The measurements of thermophysical and crystalline properties were conducted to propose the use of binary structure H (sH) hydrates of 1-methylpiperidine for carbon capture and storage (CCS). 1-Methylpiperidine is one of the most effective large guest compounds to relax the phase equilibrium conditions of binary sH clathrate hydrates. To reduce energy consumption in hydrate-based CCS, the hydrates should be formed as close to room temperature and ambient atmospheric pressure as possible. Phase equilibrium conditions of hydrates formed in the N2 + 1-methylpiperidine + water, CO2 + 1-methylpiperidine + water, and N2 + CO2+ 1-methylpiperidine + water systems were measured. Powder X-ray diffraction and gas composition analyses were also conducted. In the N2 + 1-methylpiperidine + water system, the binary structure H hydrate was formed under milder phase equilibrium conditions with higher temperature and lower pressure values, as compared to those of N2 + neohexane hydrate and pure N2 hydrate. In the CO2 + 1-methylpiperidine + water and N2 + CO2 + 1-methylpiperidine + water systems, structure I (sI) hydrates were formed. This is attributed to the chemical reaction between CO2, 1-methylpiperidine, and water in these systems, which prevents the sH hydrate formation. The composition of N2 + CO2 gas encapsulated into the binary sI hydrate was N2:CO2 = 0.20:0.80. CO2 capture was successful with the sI hydrate.

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Growth dynamics and morphology of D<inf>2</inf>O + HFC-134a clathrate hydrate crystal toward tritiated water separation

Kamiya L., Ohmura R.

Chemical Engineering Communications 211 ( 8 ) 1191 - 1198 2024

ISSN 00986445

This work represents the crystal growth and morphology of Deuterium water (D2O) and HFC-134a clathrate hydrate toward enhancing the hydrate-based tritiated water separation method. The utilization of the method involves the use of D2O + HFC-134a hydrate as a substrate to capture tritiated water. It is imperative to have a comprehensive understanding of the morphology of each crystal and the precise temperature and pressure conditions required for their production, given that the substrate consists of individual crystals. Experiments were conducted within Δ (Formula presented.) range from 1.0 K to 7.8 K. The pressure was set at 0.305 to 0.398 MPa to avoid the liquefaction of HFC-134a. The results revealed that at Δ (Formula presented.) less than 5.2 K, the hydrate crystals were plates and polyhedrons with a size of 1.0–3.0 mm. When Δ (Formula presented.) exceeded 5.2 K, the crystals of columnar or dendritic morphologies were observed. They formed elongated shapes of 3.0 mm in length and 0.1 mm in width. Columnar or dendritic crystals are suitable for increasing surface area. In contrast plate and polyhedral crystals decrease the surface area of the substrate and reduce flow resistance. Selecting the favorable crystalline form to intensify the equipment and processes is essential.

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Unusual promotion/inhibition effect of polyethylenimine on CO<inf>2</inf>/CH<inf>4</inf> hydrate formation: A potential green chemical additive for CH<inf>4</inf>-CO<inf>2</inf> replacement process

Ho Y.H., Khoo Y.Z., Chen Y.P., Ohmura R., Chen L.J.

Chemical Engineering Journal 472 2023.09

ISSN 13858947

The unusual behavior of a new class of compounds that selectively function as either promoters or inhibitors of gas hydrate formation depending on the process conditions has made their exploration increasingly appealing. In this study, polyethylenimine (PEI) exhibits desirable functionality that may be a candidate for environmentally benign compounds. The present work investigated PEI's thermodynamic and kinetic influence on the formation of CH4 and CO2 hydrates for two PEI concentrations (0.5 and 5.0 mass%) and two PEI molecular weights (25,000 and 750,000 g/mol). The isochoric method was applied to measure the hydrate-liquid water–vapor-three-phase-coexisting (H-LW-V-3PC) phase boundary. PEI is a thermodynamic inhibitor regardless of CH4 or CO2 as a hydrate former, and 0.5 mass% PEI system exhibits the highest average suppression temperatures of 0.25 and 0.62 K, respectively. Kinetic findings, such as induction time, initial hydrate formation rate, and nucleation rate, on the other hand, revealed that PEI could act differently in response to specific hydrate formers. PEI kinetically inhibits CH4 hydrates formation but promotes the formation of CO2 hydrates. This promotion effect is attributed to PEI's high CO2 absorption ability to enhance the solubility of CO2. This unique behavior of PEI presents appealing advantages in the natural gas hydrate exploitation field due to their potential for greater operational flexibility and minimal environmental impact.

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Renewed Measurements of Carbon Dioxide Hydrate Phase Equilibrium

Ito H., Gibo A., Shiraishi S., Yasuda K., Ohmura R.

International Journal of Thermophysics 44 ( 8 ) 2023.08

ISSN 0195928X

This paper investigates the phase equilibrium conditions in the carbon dioxide hydrate forming system. Carbon dioxide hydrate can be utilized for carbon capture, salt manufacture, carbonated solid foods and tritium water concentration, so the phase equilibrium conditions have been substantially reported so far. However, the data from previous studies were inconsistent with each other, such as there is a difference of 1.0 K in the phase equilibrium temperature at 2 MPa. In this study, the newly three-phase (water rich liquid + hydrate + guest rich vapor) equilibrium conditions in the carbon dioxide hydrate forming system were measured at twenty different temperature conditions within the range of (271.9-282.7) K in the two different laboratories. The six pairs of the three-phase equilibrium condition data measured under equivalent pressure conditions were consistent within mutual uncertainties. The internal consistency of the data measured in this study was evaluated by the Clausius-Clapeyron equation. The data measured in this study existed within the uncertainty range of the data from several previous studies.

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Study of the Effect of Tetrabutylammonium Halide Aqueous Solutions on the Gas Storage of Methane and Carbon Dioxide

Naeiji P., Woo T.K., Ohmura R., Alavi S.

Energies 16 ( 13 ) 2023.07

In this study, the effect of tetrabutylammonium halide aqueous solutions on the gas storage of CH4 and CO2 gases were studied with molecular dynamics (MD) simulations. The results show that the surface tension and the gas molecules adsorbed at the interface decreases and increases, respectively, in the presence of TBAX (X: Br, Cl, F) in the aqueous phase compared to pure water at similar gas pressures. Both of these factors may facilitate gas uptake into cages during semi-clathrate hydrate formation. CO2 showed a stronger intermolecular interaction with the water molecules since it was preferentially adsorbed at the interface, leading to a higher surface density as compared to CH4. Moreover, the relative increase in CH4 adsorption on the surface was because of the hydrophobic interactions between the CH4 molecules and the n-alkyl chains of the cation. The counter-ions of TBAXs can affect their surface activity. TBAX salts enhance the tetrahedral ordering of water molecules at the interface compared to the bulk, leading to a potential mechanism for forming semi-clathrate hydrates.

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Tritiated water removal method based on hydrate formation using heavy water as co-precipitant

Nakamura S., Awata T., Kiyokawa H., Ito H., Ohmura R.

Chemical Engineering Journal 465 2023.06

ISSN 13858947

A separation method of tritium has been developed based on co-precipitation of tritiated water on porous heavy water (D2O) based clathrate hydrate. The tritium was semi-continuously removed by a circulating flow of tritium-containing light water through the D2O hydrate media crystallized in advance. The tritium concentration of 4.77 × 105 Bq/kg was reduced to 1.55 × 103 Bq/kg with HFC-134a hydrate at 0.35 MPa for 1 h, while tritiated water treatment at a concentration of 1010 Bq/kg or greater is eligible with the conventional detritiation methods. Near the D2O hydrate surfaces, solid solutions with higher concentrations of tritiated water were deposited on the hydrate substrate than those in the liquid phase. The semi-serialized operation of hydrate based detritiation is capable of high-rate processing as well as energy and resource saving. This method could be a candidate treatment for huge quantities of water with low concentration tritium discharged from nuclear fusion power generation system.

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Continuous hydrate-based CO<inf>2</inf> separation from H<inf>2</inf> + CO<inf>2</inf> gas mixture using cyclopentane as co-guest

Misawa T., Ishikawa T., Takeya S., Alavi S., Ohmura R.

Journal of Industrial and Engineering Chemistry 121 228 - 234 2023.05

ISSN 1226086X

CO2 separation from H2 + CO2 gas mixture is a necessary technology for a stable supply of blue hydrogen. Among CO2 separation technology, hydrate-based CO2 separation is an environmentally and economically superior technology. Cyclopentane (CP) was selected as guest compound to enable hydrate-based CO2 separation under thermodynamic conditions closer to normal pressure and temperature. Hydrate-based continuous CO2 separation experiments are conducted in the H2 + CO2 + CP + H2O system at 284 K. The results of these experiments showed that mole fraction of H2 in the gas phase reached 0.9 at the steady state in the H2 + CO2 + CP + H2O system after the CO2 was extracted via hydrate formation. At the same time, more H2 was incorporated into the mixed hydrate during this process as the concentration of H2 in the gas phase increases post hydrate formation. Therefore, it was demonstrated that hydrate-based CO2 separation was successful in H2 + CO2 + CP + H2O system at 284 K but there is also increase of energy costs caused by H2 loss. The PXRD results identified H2 + CO2 + CP hydrate as structure II hydrate. Although H2 + CO2 + Tetrahydropyran (THP) hydrate also forms structure II hydrate, more H2 is encapsulated in the H2 + CO2 + CP mixed hydrate than in the H2 + CO2 + THP mixed hydrate. This difference may be caused by the difference in the lattice constants of CP and THP hydrates, which arises from the difference in molecular size of CP and THP, from the differences between the large guest–host interactions, and from differences arising from hydrogen bonding of THP with the host water framework which can decrease the H2 holding capacity. In this study, it was revealed that the molecular diameter of the guest molecules need also to be considered in addition to the phase equilibrium conditions of the hydrates when selecting guest compound of hydrates.

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Thermodynamic stability and characterization of double clathrate hydrate with carbon dioxide + cyclopentane + deuterium oxide

Maruyama M., Nagayama S., Misawa T., Takeya S., Ohmura R.

Journal of Chemical Thermodynamics 179 2023.04

ISSN 00219614

This paper reports characterization of clathrate hydrate formed in CO2 + cyclopentane + deuterium oxide (D2O) system with the phase equilibrium determination and the powder X-ray diffraction (PXRD) measurements towards the development of hydrate-based tritium separation technology. Four-phase (CO2 gas + liquid cyclopentane + liquid D2O + hydrate) equilibrium conditions were measured using the isochoric procedure in the pressure range from 0.279 MPa to 2.735 MPa and the temperature range from 285.35 K to 293.65 K. The equilibrium temperature of CO2 + cyclopentane + D2O system is always higher by 2.0 K to 2.4 K compared to that of CO2 + cyclopentane + H2O system. The detailed crystallographic properties of both CO2 + cyclopentane + D2O hydrate and CO2 + cyclopentane + H2O hydrate including the lattice constants, the radii and volumes of each cage and the cage occupancy were estimated by the PXRD analysis. Based on the obtained results, implications for the development and operation of D2O-hydrate-based process are discussed.

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Measurements of the Dissociation Heats of Tetrabutylammonium Acetate and Tetrabutylammonium Hydroxide Ionic Semiclathrate Hydrates

Iwai T., Takamura S., Hotta A., Ohmura R.

International Journal of Thermophysics 44 ( 3 ) 2023.03

ISSN 0195928X

Ionic semiclathrate hydrates mainly consist of water typically together with tetrabutylammonium and tetrabutylphosphonium salts. Since ionic semiclathrate hydrates have the large dissociation heat under ambient pressure and temperature conditions, various ionic semiclathrate hydrates have been studied as safety and eco-friendly phase change materials. In this study, tetrabutylammonium acetate hydrates and tetrabutylammonium hydroxide hydrates were proposed as thermal energy storage media for air conditioning and cooling lithium-ion batteries. The dissociation heat, which was a significant thermophysical property to design thermal energy storage systems, were measured at various mass fractions. The largest dissociation heats of tetrabutylammonium acetate hydrates and tetrabutylammonium hydroxide hydrates were 212.9 ± 0.9 kJ⋅kg−1 and 200.4 ± 2.2 kJ⋅kg−1. As a result of the comparison of the dissociation heats of tetrabutylammonium acetate hydrates and tetrabutylammonium hydroxide hydrates with those of other ionic semiclathrate hydrates, it was found that tetrabutylammonium acetate hydrates and tetrabutylammonium hydroxide hydrates had the promising thermophysical properties as thermal energy storage media for air conditioning and cooling lithium-ion batteries, respectively.

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Thermally Induced Phase Transition of Cubic Structure II Hydrate: Crystal Structures of Tetrahydropyran-CO<inf>2</inf> Binary Hydrate

Takeya S., Fujihisa H., Alavi S., Ohmura R.

Journal of Physical Chemistry Letters 14 ( 7 ) 1885 - 1891 2023.02

We report a thermally induced phase transition of cubic structure II hydrates of tetrahydropyran (THP) and CO2 below about 140 K. The phase transition was characterized by powder X-ray diffraction measurements at variable temperatures. A dynamical ordering of the CO2 guests in small pentagonal dodecahedral 512 host water cages, not previously observed in the simple CO2 hydrate, occurs simultaneously with the symmetry lowering transition from a cubic structure II (space group Fd-3m with cell dimensions a = 17.3202(7) Å at 153 K) to a tetragonal (space group I41/amd with cell dimensions a = 17.484(4) Å and c = 12.145(1) Å at 138 K) unit cell. The effect of guest molecules on the phase transition at low temperatures is discussed, which demonstrates that the clathrate hydrate structures and thermodynamic properties can be modified by adjusting the size and chemical structure of larger and smaller guest molecules.

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Equilibrium properties and crystal growth of D<inf>2</inf>O + cyclopentane hydrate for sustainable tritium separation

Maruyama M., Ohmura R.

Canadian Journal of Chemical Engineering 101 ( 2 ) 718 - 725 2023.02

ISSN 00084034

This study reports thermodynamic properties and crystal growth observations of D2O + cyclopentane hydrate toward the development of a hydrate-based tritium separation process. We employed D2O as a host of hydrate with respect to the investigation into the formation of D2O hydrate substrate, which is a core component of the tritium separation process. The hydrate phase equilibrium temperature in the liquid D2O + liquid cyclopentane system was 3.2°C higher than the corresponding H2O hydrate. Experiments on crystal growth were conducted at temperatures ranging from 5.1 to 8.5°C under atmospheric pressure. Under each thermodynamic condition, polygonal hydrate crystals appeared, growing along the D2O/cyclopentane interface. The geometric shape and size of the crystals varied depending on the temperature. The variation in crystal morphology was comparable to that of the H2O + cyclopentane hydrate. Implications based on the obtained results for the hydrate-based isotopic water separation process design are discussed.

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Thermophysical Properties of Ionic Semiclathrate Hydrate Formed with Tetrabutylphosphonium Malonate

Iwai T., Oguro S., Ota I., Hiraga K., Hotta A., Ohmura R.

International Journal of Thermophysics 44 ( 2 ) 2023.02

ISSN 0195928X

Ionic semiclathrate hydrate is a crystalline compound mainly composed of water, which can dissociate at ordinary pressure and temperature. Ionic semiclathrate hydrates have been widely studied to develop prospective green and safety phase change materials utilized in a thermal energy storage system to cool batteries, in air conditioning, and in a cold chain system. The thermophysical properties, such as equilibrium temperature and dissociation heat, and the mass fraction dependence of such properties need to be carefully investigated to design such systems. In this study, the equilibrium temperature and the dissociation heat of tetrabutylphosphonium malonate ionic semiclathrate hydrates were experimentally determined at various mass fractions through an established method: the maximum value of the dissociation heat was 179.70 kJ·kg−1 at w = 0.357 and the equilibrium temperature was 8.9 °C at w = 0.357. By comparing tetrabutylphosphonium malonate ionic semiclathrate hydrates with other media in terms of the measured equilibrium temperature and the dissociation heat, the usability of the hydrates as thermal energy storage media for general air conditioning was discussed.

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Zero emissions, low-energy water production system using clathrate hydrate: Engineering design and techno-economic assessment

Maruyama M., Tomura S., Yasuda K., Ohmura R.

Journal of Cleaner Production 383 2023.01

ISSN 09596526

Seawater desalination via the crystallization using clathrate hydrate is a promising technology for displacing conventional desalination processes, yet the technology immaturity and poor cost performance are the issues to be resolved. In this study, conceptual designs of hydrate-based dual functional plant (desalination and salt production) utilizing the eutectic crystallization of hydrate and NaCl dihydrate have been presented on an industrial scale with the capacity of 24 m3/day. The conceptual design proposed in this study focuses on detailed and executive aspects, including the size of individual reactors, the selection of pumps, and the setting of operating temperature and pressure conditions. The process designs help meet these present demands on hydrate-based desalination and conform to the global standards of minimizing energy requirement and the disposal of environmental pollutants. Hydrate-based plant was designed as a novel Zero Liquid Discharge (ZLD) process to produce potable water and salt simultaneously, with the recovery ratio of pure water from seawater achieving 95%. The design-based cost estimation showed that the annual operating cost is estimated US$2.29/m3 for cyclopentane-hydrate-based plant and US$3.64/m3 for CO2-hydrate-based plant. The results suggest that the hydrate-based plants will bring gross profit comparable to the reported ZLD plants; that is, the gross profit will achieve US$20 per 1 m3 of water production. In addition to these two improvements over the existing plants, the hydrate-based process designs also exhibit favorable energy requirement compared to the eutectic system of ice. This design-based study may contribute to the promotion of additional construction of hydrate-based process unit to the existing reverse osmosis plant or even the new construction of hydrate-based desalination plant worldwide.

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Phase equilibrium conditions in cyclopentane hydrate forming systems coexisting with sodium chloride aqueous solution under atmospheric pressure and vacuum condition

Kamochi K., Tripathi A., Taoka M., Ohmura R., Yasuda K.

Journal of Chemical Thermodynamics 175 2022.12

ISSN 00219614

The equilibrium condition measurements were performed in the cyclopentane clathrate hydrate forming systems coexisting with sodium chloride as a technological basis for the development of seawater desalination technology using clathrate hydrates. The experiments were performed in the system under vacuum condition in addition to the system under atmospheric pressure. The equilibrium conditions in the system under the vacuum condition are essential to accurately construct the phase diagram in the cyclopentane clathrate hydrate forming system without the effects of the surrounding air. The equilibrated phases were sodium chloride aqueous solution + cyclopentane clathrate hydrate + liquid cyclopentane + vapor cyclopentane in the system under the vacuum condition. The concentration of sodium chloride investigated in this study, wNaCl, was 0 ≤ wNaCl ≤ 0.210 in mass fraction. The equilibrium temperature in both systems decreased with increasing wNaCl. The equilibrium temperature at a fixed concentration of sodium chloride under the vacuum condition was lower than that under the atmospheric pressure. It was attributed to the compression by the atmospheric pressure in addition to the incorporation of molecules constituting the atmospheric air.

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Synthesis and thermophysical properties of Tetrabutylammonium picolinate hydrate as an energy storage phase change material for cold chain

Yamamoto K., Iwai T., Hiraga K., Miyamoto T., Hotta A., Ohmura R.

Journal of Energy Storage 55 2022.11

Ionic semiclathrate hydrates, the water-based phase change materials (PCMs) have potential for thermal energy storage media. There are a number of hydrates, reported in the literature, which are suitable as PCMs for air conditioning system of the required temperature range 10–15 °C. In this study, Tetrabutylammonium picolinate hydrate (TBAPi hydrate) was newly synthesized as a PCM for the cold chain, which has a lower phase equilibrium temperature than the previously reported hydrates. Thermophysical properties of TBAPi hydrate were experimentally measured. The hydrate dissociation heat was determined using a differential scanning calorimeter (DSC). The phase equilibrium temperature was measured by visually observing system with a CMOS camera and microscope. Also, the cycling test was conducted to confirm the long-term stability of thermophysical properties. The largest dissociation heat was 157.7 ± 4.9 kJ・kg−1 at a mass fraction of TBAPi aqueous solution, wTBAPi of 0.37. The highest phase equilibrium temperature of TBAPi hydrate was 5.5 °C at 0.34 ≤ wTBAPi ≤ 0.36. These thermophysical properties did not change even after 200 cycles of hydrate formation and dissociation. Based on the experimental results, TBAPi hydrate can be applied to the transport and storage of vaccines, blood packs, and perishable foods.

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Measurements of phase equilibrium temperature and dissociation heat of tetrabutylphosphonium glutarate ionic semiclathrate hydrate

Iwai T., Ohta I., Hiraga K., Kashima K., Hotta A., Ohmura R.

Fluid Phase Equilibria 562 2022.11

ISSN 03783812

Thermophysical properties such as phase equilibrium temperature and dissociation heat are important to determine the performance of phase change materials targeting thermal energy storage. The phase equilibrium temperature and dissociation heat of tetrabutylphosphoniumglutarate ionic semiclathrate hydrate were measured in this study. The highest phase equilibrium temperature of tetrabutylphosphoniumglutarate hydrate was experimentally determined 287.4 K at the mass fraction 0.347 and 0.357. The largest dissociation heat was 193.3 ± 1.6 kJ/kg at the mass fraction 0.357. The measurement results in this work show that the dissociation heat can be utilized in the suitable temperature range targeting general air conditioning and data center.

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Molecular dynamics simulations of interfacial structure, dynamics, and interfacial tension of tetrabutylammonium bromide aqueous solution in the presence of methane and carbon dioxide

Naeiji P., Woo T.K., Ohmura R., Alavi S.

Journal of Chemical Physics 157 ( 15 ) 2022.10

ISSN 00219606

The interfacial behavior of tetrabutylammonium bromide (TBAB) aqueous solutions in the absence of gas and the presence of methane and carbon dioxide gases is studied by molecular dynamics simulations. The aqueous TBAB phase, at concentrations similar to the solid semiclathrate hydrate (1:38 mol ratio), has a smaller interfacial tension and an increase in the gas molecules adsorbed at the interface compared to that in pure water. Both these factors may contribute to facilitating the uptake of the gases into the solid phase during the process of semiclathrate hydrate formation. At similar gas pressures, CO2 is adsorbed preferentially compared to CH4, giving it a higher surface density, due to the stronger intermolecular interactions of CO2 molecules of the solution at the interface. The increase in relative adsorption of CH4 at the solution surface compared to that in pure water surface is due to the hydrophobic interactions between the n-alkyl chains of the TBA+ cation and methane gas.

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Development of dual functional methodology for seawater desalination and salt manufacture by carbon dioxide hydrate formation

Gibo A., Nakao S., Shiraishi S., Takeya S., Tomura S., Ohmura R., Yasuda K.

Desalination 539 2022.10

ISSN 00119164

Clathrate-hydrate-based seawater desalination is a novel technology that is performed by reaction between seawater and guest compounds to obtain fresh water. This study proposed a dual functional methodology for seawater desalination and salt manufacture by using carbon dioxide clathrate hydrate. In this methodology, the clathrate hydrate formation continues until the concentration of electrolytes in unreacted brine reaches the saturated solubility for the salt precipitation. The visual observation of the clathrate hydrate formation and the salt precipitation coupled with the analysis utilizing the powder X-ray diffraction (PXRD) technique was implemented to demonstrate the methodology. The carbon dioxide clathrate hydrate formation was first performed with sodium chloride aqueous solution. The carbon dioxide clathrate hydrate crystals floated on high salinity water. This experiment was followed by the occurrence of the sodium chloride dihydrate precipitation upon the carbon dioxide clathrate hydrate formation. The formed compounds, carbon dioxide clathrate hydrate and sodium chloride dihydrate, were identified by PXRD analysis. The mass fraction of the compounds was also determined by PXRD.

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Continuous CO<inf>2</inf>Separation from a N<inf>2</inf>+ CO<inf>2</inf>Gas Mixture Using Clathrate Hydrate: Insights into Sustainable Post-combustion Carbon Capture

Maruyama M., Kao S., Kiyokawa H., Takeya S., Ohmura R.

Energy and Fuels 36 ( 18 ) 10601 - 10609 2022.09

ISSN 08870624

Clathrate-hydrate-based CO2 capture from a post-combustion N2 + CO2 gas mixture has been experimentally investigated for decarbonization. In this study, we performed hydrate-based continuous CO2 separation experiments for N2 + CO2 + tetrahydropyran (THP) + water system. The experimental conditions were set at 280.1 K under 3.0 MPa with THP mass fractions wTHP of 0.22 and 0.11. For each experimental run, the time-dependent changes in compositions in the gas phase and the hydrate slurry were recorded hourly until the system reached a steady state. The cage occupancies of N2 and CO2 in the structure II 512 small cages were determined to be 43 and 24%, respectively, with the powder X-ray diffraction analysis. The obtained results showed that the continuous carbon capture is a practicable scheme, yet the CO2 concentration rate and CO2 recovery ratio are comparable to or lower than those of the pre-combustion systems reported in previous studies. Still, our investigation revealed that the development of an efficient hydrate formation method, such as the improvement of the geometry of mixing impellers, could enhance the CO2 recovery ratio for the continuous operation.

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Synthesis and evaluation of green phase change materials for efficient air conditioning by tetrabutylphosphonium phosphate ionic semiclathrate hydrate

Iwai T., Miyamoto T., Kurokawa N., Hotta A., Ohmura R.

Journal of Energy Storage (Journal of Energy Storage) 52 2022.08

A tetrabutylammonium bromide (TBAB) hydrate is the only ionic semiclathrate hydrate that has been commercialized as a medium for efficient thermal energy storage targeting general air conditioning. However, TBAB is an environmental pollutant, while liquid water and ice that have been widely used as conventional media, also have difficulty in increasing the thermal energy storage density as well as the coefficient of performance (COP) of a refrigerator to form solid. In this study, a tetrabutylphosphonium phosphate ((TBP)3PO4) hydrate was proposed as an alternative green medium. The dissociation heat and the phase equilibrium temperature, which were both crucial factors to evaluate the thermal energy storage density, and COP was experimentally determined. It was found that the maximum dissociation heat was 154.1 ± 2.0 kJ・kg−1 at the mass fraction of 0.309. The highest phase equilibrium temperature was 10.0 °C at the mass fractions of 0.290, 0.299, and 0.309. The thermal energy storage density of (TBP)3PO4 hydrates was 3.7 times larger than that of water. (TBP)3PO4 hydrates increased the COP of a refrigerator to form solid by 42% as compared with ice, indicating the potential size-reduction of conventional devices with the decrease in the power consumption of a refrigerator. The effective balance between environmental protection and the system performance through (TBP)3PO4 hydrates was also discussed.

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Pinacol hydrate as a novel thermal energy storage medium for electric vehicles

Kiyokawa H., Kondo Y., Koyama R., Kurokawa N., Atsushi H., Alavi S., Ota I., Ohmura R.

Journal of Energy Storage (Journal of Energy Storage) 51 2022.07

Movement towards the gradual replacement of gasoline combustion vehicles to electrical vehicles is occurring on a global scale. Heat management of lithium-ion batteries (LIB) is necessary for long-term operation and safety of the power sources of electrical vehicles. This research suggests pinacol hydrate as a phase change material (PCM) for use as an alternative cooling media for LIB. The pinacol hydrate crystallizes under atmospheric pressure and temperatures around 45 °C, which are compatible with LIB operating conditions. Its dissociation enthalpy can control the excessive heating of the battery. The equilibrium phase transition temperature of pinacol hydrate was reported about a decade ago, but its thermal storage capacity has not been reported yet and updated quantitative measurements are required. Hence, in this study the equilibrium temperatures and dissociation enthalpies are experimentally measured for pinacol aqueous solutions prepared with mass fractions between 0.40 and 0.85. The maximum thermal storage capacity is measured by differential scanning calorimetry to be 301.9 kJ/kg for mass fraction of 0.50 which is compatible with operating conditions of up to 45.6 °C. A minimization of reservoir tank mass by 35% of that needed for conventional technologies may be possible by using pinacol hydrate.

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Investigation of crystal growth of CO<inf>2</inf> hydrate in aqueous fructose solution for the potential application in carbonated solid foods

Shigehara S., Ohmura R.

Food Chemistry (Food Chemistry) 371 2022.03

ISSN 03088146

CO2 hydrate is applicable to solid carbonated foods. The hydrate crystal morphology, which represents the crystal size and shape, is an important characteristic that changes the texture of foods. We report an observational study of the crystal growth of CO2 hydrate in aqueous fructose solution. The difference between the phase equilibrium temperature and the experimental temperature, ΔTsub, is applied as an index of the driving force. Experiments were performed at ΔTsub range of 0.9 K to 5.4 K. At all ΔTsub, initial crystal formed at the gas-solution interface and grew along the interface. After covering the interface, the crystals grew in the liquid phase The individual crystals were identified as polyhedral with facets (ΔTsub = 0.9 K), skeletal crystals (ΔTsub = 2.0 K) and dendrites (ΔTsub = 3.0 K and 5.4 K). Based on these results, the potential effect of gas hydrate morphology on texture of foods has been discussed.

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Synthesis and thermophysical property evaluation of ionic semiclathrate hydrate formed with tetrabutylphosphonium glycine as a chilling temperature phase change material

Miyamoto T., Kurokawa N., Ota I., Hotta A., Ohmura R.

Journal of Energy Storage (Journal of Energy Storage) 45 2022.01

Ionic semiclathrate hydrate, which is formed under atmospheric pressure with sustainably safe properties, has a potential for solid-liquid phase change materials(PCMs). In this study, the thermophysical property of tetrabutylphosphonium glycine(TBPGly) hydrate containing no halogen guest compound, glycine (aminoacetic acid), was investigated to evaluate the availability as an eco-efficient thermal energy storage medium. The phase equilibrium temperature was obtained through visual observation method. The heat flow rate curve behavior and dissociation heat were measured via differential scanning calorimetry(DSC). In the dissociation process, a single hydrate dissociation peak emerged, indicating TBPGly hydrate has one type of crystallographic structure. The concentration dependency of the TBPGly aqueous solution on the equilibrium temperature and the dissociation heat was confirmed. The highest equilibrium temperature of 5.8 °C was confirmed at the fraction range wTBPGly =0.368 or xTBPGly =0.0306, and the largest dissociation heat was 177.7 kJ·kg−1 at the fraction range wTBPGly =0.377or xTBPGly =0.0318. The estimated hydration number in the congruent composition was found to be in 31.2 to 32.5. In addition, based on the measured physical property, the optimum operating temperature and volume fraction of TBPGly hydrate was evaluated to determine the concentration for the practical cooling system. These data revealed TBPGly hydrate is available as a solid or slurry PCM under the operating temperature range 2 °C to 5.8 °C. The experimental data as well as the illustrative calculations contribute to accelerate the expansion in the application range, and provide the prospect in selecting the suitable composition toward the actual hydrate-based cooling system.

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Investigation of the thermodynamic properties of hydrates as cooling phase change materials for their implementation in electric vehicles

Kiyokawa H., Miyamoto T., Takeya S., Ota I., Iwai T., Hotta A., Ohmura R.

New Journal of Chemistry (New Journal of Chemistry) 46 ( 19 ) 9214 - 9221 2022

ISSN 11440546

Electric vehicles (EVs) play key roles in realizing a sustainable society. Lithium-ion batteries (LIBs) implemented in EVs deteriorate due to significant temperature changes. To maintain LIBs in an appropriate temperature range, a competitive thermal energy storage (TES) medium is needed. Phase change materials (PCMs) that can utilize their latent heat have great potential. In this study, we focused on piperazine hexahydrate as a promising candidate for a PCM and investigated its thermodynamic properties that are essential for practical design. The equilibrium temperature and dissociation enthalpy were determined in the mass fraction range of 0.250 to 0.550. The results showed that piperazine hexahydrate had a maximum equilibrium temperature of 42.9 °C and a maximum dissociation enthalpy of 250.0 ± 3.7 kJ kg−1 at a mass fraction of 0.443, which is the congruent point of piperazine hexahydrate. Piperazine hexahydrate can be utilized as a PCM in the temperature range of 34.4 °C to 42.9 °C. By utilizing piperazine hexahydrate instead of a conventional water-cooling system, the volume of the TES tank may be reduced by 31% approximately. The crystal system of the piperazine hexahydrate prepared in the present study was determined to be pseudomonoclinic by powder X-ray diffraction (PXRD) measurements, which is the same as that reported in the literature.

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Thermophysical Properties of a Promising Material for Thermal Energy Storage Synthesized by Tetrabutylphosphonium Malonate and Water

Iwai T., Oguro S., Ohta I., Hotta A., Ohmura R.

Proceedings of IEEE Asia-Pacific Conference on Computer Science and Data Engineering, CSDE 2022 2022

Thermal energy storage for air conditioning is increasingly becoming important because the fluctuating output of renewable energy and the growing cooling demand will need to be addressed. In this study, we proposed tetrabutylphosphonium malonate hydrate as an environment friendly thermal energy storage medium for air conditioning. Equilibrium temperature and dissociation heat, which were significant thermophysical properties for commercialization, were experimentally determined at three mass fractions of tetrabutylphosphonium malonate aqueous solution. The maximum value of equilibrium temperature was determined to be 8.9 °C. The largest dissociation heat was measured to be 148.1 kJ/kg. These results indicate that tetrabutylphosphonium malonate hydrate has appropriate thermophysical properties for a thermal energy storage medium.

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Phase Equilibrium for Clathrate Hydrate Formed in Deuterium Oxide + CO<inf>2</inf>+ Cyclopentane System: Application to Low-Concentration Tritium Separation

Maruyama M., Misawa T., Ohmura R.

Proceedings of IEEE Asia-Pacific Conference on Computer Science and Data Engineering, CSDE 2022 2022

This paper reports pressure-temperature conditions for liquid + hydrate + vapor phase equilibrium of hydrate formed with deuterium oxide (D2O), CO2 and cyclopentane. The aim of this study is to obtain the equilibrium properties of the formed hydrate for the application to hydrate-based tritium separation process. Measurements with batch isochoric method were performed. The pressure and temperature ranges of measurement were from 1.63 MPa to 2.46 MPa and from 290.6 K to 293.4 K. The obtained results indicate that D2O + CO2+ cyclopentane hydrate is formed in milder conditions than H2O + CO2+ cyclopentane hydrate by 2.1 K at the given pressure conditions.

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Crystal growth of clathrate hydrate formed with H<inf>2</inf> + CO<inf>2</inf> mixed gas and tetrahydropyran

Maruyama M., Matsuura R., Ohmura R.

Scientific Reports (Scientific Reports) 11 ( 1 ) 2021.12

Hydrate-based gas separation technology is applicable to the CO2 capture and storage from synthesis gas mixture generated through gasification of fuel sources including biomass. This paper reports visual observations of crystal growth dynamics and crystal morphology of hydrate formed in the H2 + CO2 + tetrahydropyran (THP) + water system with a target for developing the hydrate-based CO2 separation process design. Experiments were conducted at a temperature range of 279.5–284.9 K under the pressure of 4.9–5.3 MPa. To simulate the synthesis gas, gas composition in the gas phase was maintained around H2:CO2 = 0.6:0.4 in mole fraction. Hydrate crystals were formed and extended along the THP/water interface. After the complete coverage of the interface to shape a polycrystalline shell, hydrate crystals continued to grow further into the bulk of liquid water. The individual crystals were identified as hexagonal, tetragonal and other polygonal-shaped formations. The crystal growth rate and the crystal size varied depending on thermodynamic conditions. Implications from the obtained results for the arrangement of operating conditions at the hydrate formation-, transportation-, and dissociation processes are discussed.

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Measurement and analysis of interfacial tension of decane/water system pressurized with methane + ethane + propane gas mixture

Kiyokawa H., Kodera M., Lassiège M., Alavi S., Ohmura R.

Journal of Natural Gas Science and Engineering (Journal of Natural Gas Science and Engineering) 96 2021.12

ISSN 18755100

Blockages in natural gas and oil pipelines can be caused by the aggregation of clathrate hydrate crystals which form at the oil-water-gas interfaces. Knowledge of interfacial tensions between components are crucial to understanding the interface physical chemistry and numerically simulating pipeline multiphase flow. This study measures the effect of the presence of natural gas components on the oil-water interfacial tension and its potential implications on flow assurance in oil-gas pipelines. Decane is used to mimic oil and is saturated with the gaseous mixture of methane, ethane, and propane as is consistent with simulations of multiphase dynamics. Water droplets were generated in decane and photographed through a window using pendant drop method in order to determine the oil-water interfacial tension. This study examined both mechanical and thermodynamic phenomena by considering interfacial tension under different pressure/temperature conditions covering the natural gas hydrate formation region. The effect of the gas mixture composition and pressure on the interfacial tension was determined at different temperatures in the range of pipeline operating conditions. The behavior was explained from both experimental and theoretical points of view. At lower pressures, the presence of the C2 and C3 natural gas components lowers the decane-water interfacial tension compared to the case of the decane-water-methane system. In particular, the pressure dependence of the interfacial tension was found to be almost five times higher than that in the absence of C2 and C3. By decreasing the interfacial tension, the presence of ethane and propane may facilitate the mixing of the water and oil phases in pipelines, therefore affecting the rate of hydrate formation.

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Improved Operation of Continuous Ozone Hydrate Production

Hatsugai T., Kiyokawa H., Takeya S., Ohmura R.

Chemical Engineering and Technology (Chemical Engineering and Technology) 44 ( 9 ) 1677 - 1685 2021.09

ISSN 09307516

In a previous study, we have experimentally demonstrated the continuous formation of O3+O2+CO2 hydrate. Here, improved results for the O3+O2+CO2 hydrate formation are reported. By forming O3+O2+CO2 hydrate at a low temperature and higher O3 gas concentration in the gas phase, the O3 concentration in the hydrates was increased to be 0.41 mass %, which was 1.6 times higher than our past record. One-quarter reduction of the induction time for O3+O2+CO2 hydrate formation was also achieved by raising the initial volume ratio of CO2 in the feed gas in the range of 2–2.9 times that of our previous study. Also, the overall heat transfer coefficient during O3+O2+CO2 hydrate continuous formation was experimentally determined.

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Simultaneous Crystallization of Cyclopentane Hydrate and Sodium Chloride for Desalination and Salt Manufacture

Tanaka M., Tsugane K., Suga D., Tomura S., Ohmura R., Yasuda K.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 9 ( 27 ) 9078 - 9084 2021.07

Simultaneous crystallization of cyclopentane hydrate and sodium chloride dihydrate was implemented to demonstrate a dual-functional system for hydrate-based seawater desalination and salt manufacture that could be performed with zero emission. A sodium chloride aqueous solution having an initial mass fraction of sodium chloride of 0.235 or 0.264 was used for the experiments as an alternative to seawater. When using the aqueous solution having a sodium chloride concentration of 0.264 in mass fraction, the precipitation of polyhedral sodium chloride dihydrate crystals was first observed, followed by the formation of particulate cyclopentane hydrate crystals. In contrast, when using the aqueous solution having a sodium chloride concentration of 0.235 in mass fraction, the formation of particulate cyclopentane hydrate was first observed and then the particulate sodium chloride dihydrate precipitated. The formed cyclopentane hydrate and the precipitated sodium chloride dihydrate were separated by the remaining sodium chloride aqueous solution due to the density difference even after the agitation of the system. The eutectic temperature and concentration were determined to be 259.75 K and 0.238 in mass fraction of sodium chloride, respectively.

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Characterization of clathrate hydrate formed in H<inf>2</inf> + CO<inf>2</inf> + tetrahydropyran + water system as carbon capture materials

Kodera M., Takeya S., Lassiège M., Alavi S., Ohmura R.

Fuel (Fuel) 295 2021.07

ISSN 00162361

This paper reports the thermodynamic and crystallographic characterization of the clathrate hydrate formed in H2 + CO2 + tetrahydropyran (THP) + water system by phase equilibrium measurements and powder X-ray diffraction measurements with a goal of developing a hydrate-based carbon capture technology in an integrated coal gasification combined cycle. The four-phase [(H2 + CO2) gas + water liquid + THP liquid + hydrate] equilibrium conditions were measured with two series of gas compositions (around H2:CO2 = 0.7:0.3 and 0.9:0.1 in mole fractions) in the range of 2.64 MPa to 7.51 MPa. At around H2:CO2 = 0.7:0.3 in gas phase, the equilibrium temperatures in (H2 + CO2) gas + THP + water system are always higher by approximately 9 to 10 K compared to the equilibrium temperatures of H2 + CO2 + water system. This means that THP acts as the hydrate thermodynamic promoter. The equilibrium conditions in (H2 + CO2) gas + THP + water system, which is only considered with CO2 partial pressure, greatly agree with those in CO2 + THP + water system. Therefore, the equilibrium conditions in (H2 + CO2) gas + THP + water system would only depend on the partial pressure of CO2. Moreover, the crystallographic structure of the hydrate formed in H2 + CO2 + THP + water system was identified to be structure II, which is the same structure as the hydrate formed in H2 + CO2 + water system. These results can contribute to the study of a hydrate-based gas separation and carbon capture.

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Thermal energy storage performance of tetrabutylammonium acrylate hydrate as phase change materials

Kiyokawa H., Tokutomi H., Ishida S., Nishi H., Ohmura R.

Applied Sciences (Switzerland) (Applied Sciences (Switzerland)) 11 ( 11 ) 2021.06

Kinetic characteristics of thermal energy storage (TES) using tetrabutylammonium acrylate (TBAAc) hydrate were experimentally evaluated for practical use as PCMs. Mechanical agitation or ultrasonic vibration was added to detach the hydrate adhesion on the heat exchanger, which could be a thermal resistance. The effect of the external forces also was evaluated by changing their rotation rate and frequency. When the agitation rate was 600 rpm, the system achieved TES density of 140 MJ/m3 in 2.9 hours. This value is comparable to the ideal performance of ice TES when its solid phase fraction is 45%. UA/V (U: thermal transfer coefficient, A: surface area of the heat ex-change coil, V: volume of the TES medium) is known as an index of the ease of heat transfer in a heat exchanger. UA/V obtained in this study was comparable to that of other common heat exchang-ers, which means the equivalent performance would be available by setting the similar UA/V. In this study, we succeeded in obtaining practical data for heat storage by TBAAc hydrate. The data obtained in this study will be a great help for the practical application of hydrate heat storage in the future.

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Thermodynamic analysis of hydrate-based refrigeration cycle

Matsuura R., Watanabe K., Yamauchi Y., Sato H., Chen L.J., Ohmura R.

Energy (Energy) 220 2021.04

ISSN 03605442

Clathrate hydrates (hydrates) have a larger dissociation heat than an evaporation heat of the working fluid of conventional refrigeration systems. This property can be applied to a novel refrigeration system. In this study, theoretical performance analysis of the refrigeration system utilizing hydrates as its working medium was conducted. We modeled the thermodynamic cycle of the hydrate-based refrigeration system composed of following processes: adiabatic compression, hydrate formation at high temperature, adiabatic expansion, and hydrate dissociation at low temperature. Based on the thermodynamic cycle, the coefficient of performance (COP) of the hydrate cycle was theoretically formulated with thermodynamic state functions of the working medium. Using the formula, COP was calculated on the three hydrate forming systems including HFC-32 + cyclopentane (CP) + water, Kr + CP + water, and HFC-41 + CP + water. The analysis based on the calculated results revealed that the dissociation heat of hydrates and the enthalpy change of guest gas were dominant factors to COP and polyatomic molecules would be appropriate for guest gas of hydrates. The maximum COP values on the hydrate cycle were comparable to those of the reversed Rankine cycle. The hydrate-based refrigeration system outperformed conventional refrigeration systems in terms of safety and environmental-friendliness.

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Crystal Growth of Structure-H Hydrate with Water-Soluble Large Molecule Guest Compound: 1-Methylpiperidine as a Case Study

Matsuura R., Alavi S., Ohmura R.

Crystal Growth and Design (Crystal Growth and Design) 21 ( 2 ) 1351 - 1357 2021.02

ISSN 15287483

This paper presents visual observations of formation and growth of structure-H hydrate formed with methane and 1-methylpiperidine (MPD). MPD is one of the water-miscible guest compounds which form structure-H hydrates with a help gas. This guest promotes hydrate formation of the help gas and has an advantage of omitting the dissolution process in water during potential industrial utilization. The observed crystal growth dynamics were categorized into two types depending on the subcooling temperature ΔTsub, the difference between the phase equilibrium and experimental temperatures. At ΔTsub = 2.8 K, the gas/liquid interface was covered by an agglomeration of hydrate grains. No remarkable hydrate growth was recognized after coverage of the gas/liquid interface. At ΔTsub ≥ 4.9 K, hydrate crystals continued forming and growing even after the gas/liquid interface was covered by hydrates, which increased the amount of formed hydrate crystals compared to lower ΔTsub. The crystal shape changed from polygonal or platelike into pyramidal, and the size of individual crystals increased with the rise of ΔTsub, opposite the common trend where crystals become smaller at higher supercooling. Implications of the results of crystal morphology on suitable conditions for industrial utilization of this hydrate for gas capture applications are discussed.

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Characterization of the Clathrate Hydrate Formed with Fluoromethane and Pinacolone: The Thermodynamic Stability and Volumetric Behavior of the Structure H Binary Hydrate

Kondo Y., Alavi S., Takeya S., Ohmura R.

Journal of Physical Chemistry B (Journal of Physical Chemistry B) 125 ( 1 ) 328 - 337 2021.01

ISSN 15206106

To reveal the relation of guest dynamics within the structure H clathrate hydrate and its macroscopic physical properties, experimental and computational works have been conducted on the system of fluoromethane (HFC-41) and pinacolone coexisting with water. The phase boundaries of the hydrate formed from HFC-41 and pinacolone within the pressure range of (0.25-2.48) MPa and the temperature range of (277-293) K were measured. The equilibrium hydrate formation pressure incorporating HFC-41 was lowered by adding the pinacolone as a large guest molecule compound to form a sH phase compared to the HFC-41 single hydrate. Powder X-ray diffraction measurements confirmed the formation of the structure H hydrate with the HFC-41 and pinacolone binary hydrate. The lattice constants of the sH hydrate were also measured to see the effect of the help guest molecular size, which showed a different trend from that of the previous studies of sH pinacolone hydrates. Molecular dynamics simulations of the binary sH phase indicate weak hydrogen bonding of the pinacolone molecules with the water in the cages in the phase with HFC-41. The oblate HFC-41 molecules showed strong orientational preference to the equatorial planes of the D′ cages, which may explain some of the trends in the behavior of this phase.

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Phase equilibrium condition measurements in carbon dioxide hydrate forming system coexisting with seawater

Nakane R., Shimosato Y., Gima E., Ohmura R., Senaha I., Yasuda K.

Journal of Chemical Thermodynamics (Journal of Chemical Thermodynamics) 152 2021.01

ISSN 00219614

Three phase equilibrium conditions of synthetic standard (seawater + carbon dioxide hydrate + carbon dioxide gas) were experimentally determined based on the batch, isochoric procedure. The total mass fraction of the electrolytes in the synthetic standard seawater, wss, was 0.0351, 0.0700, or 0.1036 that was composed of pure water and seven salts. The equilibrium pressure–temperature conditions were as follows: 271.95 K < T < 279.05 K and 1.298 MPa < p < 3.144 MPa in the system having wss = 0.0351, 272.25 K < T < 278.15 K and 1.530 MPa < p < 3.361 MPa in the wss = 0.0700 system and 271.15 K < T < 275.65 K and 1.643 MPa < p < 2.909 MPa in the wss = 0.1036 system. The quantitative evaluation of the changes in the equilibrium temperature at a fixed pressure was performed by applying the equilibrium conditions to the Clausius–Clapeyron equation. The results are essential to design the thermodynamic conditions for the clathrate hydrate-based seawater desalination technology.

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X-Ray attenuation and image contrast in the X-ray computed tomography of clathrate hydrates depending on guest species

Takeya S., Muromachi S., Hachikubo A., Ohmura R., Hyodo K., Yoneyama A.

Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics) 22 ( 47 ) 27658 - 27665 2020.12

ISSN 14639076

In this study, X-ray imaging of inclusion compounds encapsulating various guest species was investigated based on the calculation of X-ray attenuation coefficients. The optimal photon energies of clathrate hydrates were simulated for high-contrast X-ray imaging based on the type of guest species. The proof of concept was provided by observations of Kr hydrate and tetra-n-butylammonium bromide (TBAB) semi-clathrate hydrate using absorption-contrast X-ray computed tomography (CT) and radiography with monochromated synchrotron X-rays. The radiographic image of the Kr hydrate also revealed a sudden change in its attenuation coefficient owing to the K-Absorption edge of Kr as the guest element. With a photon energy of 35 keV, X-ray CT provided sufficient segmentation for the TBAB semi-clathrate hydrate coexisting with ice. In contrast, the simulation did not achieve the sufficient segmentation of the CH4 and CO2 hydrates coexisting with water or ice, but it revealed the capability of absorption-contrast X-ray CT to model the physical properties of clathrate hydrates, such as Ar and Cl2 hydrates. These results demonstrate that the proposed method can be used to investigate the spatial distribution of specific elements within inclusion compounds or porous materials.

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Development and Continuous Operation of a Bench-Scale System for the Production of O<inf>3</inf> + O<inf>2</inf> + CO<inf>2</inf> Hydrates

Hatsugai T., Nakayama R., Tomura S., Akiyoshi R., Nishitsuka S., Nakamura R., Takeya S., Ohmura R.

Chemical Engineering and Technology (Chemical Engineering and Technology) 43 ( 11 ) 2307 - 2314 2020.11

ISSN 09307516

Ozone (O3) has many industrial applications such as in sterilization. One of the long-term O3 preservation methods is molecular storage in clathrate hydrate. In this study, an experimental system was developed for continuously forming O3 + O2 + CO2 hydrates. The parameters that affect the continuous operation of the system and that lead to increases in the concentration of O3 in the hydrates were also experimentally evaluated, implementing the method of quality engineering. After optimizing these operating parameters, the O3 storage capacity in the hydrates was measured to be 0.26 wt % at 2 h of total operation time. By X-ray diffraction, it was found that the produced sample contained hydrates, and long-term preservation for 6 months was possible at the temperature of general freezing warehouses.

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Crystal Growth of Clathrate Hydrate with Ozone: Implication for Ozone Preservation

Matsuura R., Ozawa K., Alavi S., Ohmura R.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 8 ( 41 ) 15678 - 15684 2020.10

Preservation using hydrates as a storage medium is the only technology that enables long-term and high-concentration O3 preservation. This study reports the visual observations of the crystal growth of O3-containing hydrate for the process design of the hydrate production plant. We conducted experiments with the feed gas involving O3, O2, and CO2 in the molar ratio of O3:O2:CO2 = 3.4:42.0:52.6. During observations, O3 in the mixed gas remained at 1.31-2.43 mol %, which is comparable to those of the previous experiments. The observed results of hydrate crystal growth dynamics were classified into two types, which are lateral growth along the gas/water interface and growth into the bulk of the liquid water phase. Crystal morphology varied from polygonal to columnar, dendritic, or haze like with increasing subcooling temperature relative to equilibrium. The diversity of the crystal morphology of O3-containing hydrate was comparable to those of O2 + CO2 hydrate and CO2 hydrate. The implications of the obtained results for the operating conditions of an O3-containing hydrate production plant are discussed.

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Improvement of continuous hydrate-based CO<inf>2</inf> separation by forming structure II hydrate in the system of H<inf>2</inf> + CO<inf>2</inf> + H<inf>2</inf>O + Tetrahydropyran (THP)

Kiyokawa H., Horii S., Alavi S., Ohmura R.

Fuel (Fuel) 278 2020.10

ISSN 00162361

Continuous hydrate-based CO2 separation is a compelling technology both from an environmental and economical perspective. We developed a method to continuously capture and separate CO2 from a gas mixture with H2 and determined the time-dependent changes of compositions in the gas and hydrate containing aqueous phases. Tetrahydropyran (THP), a representative water-soluble large molecular guest compound for structure II (sII) clathrate hydrate, was added in the reactor. THP forms hydrates under moderate conditions. The effects of THP mass fraction in the solution, wTHP, on the gas separation was simultaneously investigated by using wTHP = 0.11 and the stoichiometric value for sII hydrate, wTHP = 0.22. The results showed the gas phase hydrogen concentration reached steady state at 0.92 mol fraction from 0.60 in the feed gas. Also, the results demonstrated that sII hydrate has the highest CO2 loading capacity compared to ionic semi-clathrate hydrate phases. A continuous hydrate-based gas separation with sII hydrate has yet to be investigated. This study provides new experimental evidence which proves that the sII hydrate is the best structure for hydrate-based gas separation.

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Physical properties and characterization of the binary clathrate hydrate with methane + 1,1,1,3,3-Pentafluoropropane (HFC-245fa) + Water

Kodera M., Matsueda T., Belosludov R.V., Zhdanov R.K., Belosludov V.R., Takeya S., Alavi S., Ohmura R.

Journal of Physical Chemistry C (Journal of Physical Chemistry C) 124 ( 38 ) 20736 - 20745 2020.09

ISSN 19327447

This paper reports the thermodynamic and crystallographic properties of the binary clathrate hydrate with methane + 1,1,1,3,3-pentafluoropropane (HFC-245fa) by phase equilibrium measurements, powder X-ray diffraction (PXRD) measurements, and first-principles and thermodynamic calculations. The four-phase (methane gas + water liquid + HFC-245fa liquid + hydrate) equilibrium conditions are lower in pressure by approximately 2−3 MPa than those of the methane + trans-1,3,3,3tetrafluoropropene [HFO-1234ze(E)] hydrates at each temperature from 274.5 to 282.17 K, in spite of the similar molecular structure of HFC-245fa and HFO-1234ze(E). The crystallographic structure of the hydrate with methane + HFC-245fa was identified to be structure II by the PXRD measurement; although because of its molecular length, HFC-245fa would be expected to be encapsulated into a 51268 cage of structure H hydrate. First-principles calculations revealed that these thermodynamic and crystallographic phenomena are the result of two physical factors. First, the total HFC-245fa−water interactions in the cages are stronger than the HFO-1234ze(E)−water interactions due to the presence of more fluorine atoms at the two edge groups in the HFC-245fa molecule and the resulting higher dipole moment of HFC-245fa, and second, the HFC-245fa−HFC-245fa interaction is more greatly enhanced by the presence of methane compared to the HFO-1234ze(E)−HFO-1234ze(E) interactions.

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Clathrate hydrates at temperatures below the freezing point of water: A review

Nagashima H.D., Miyagi T., Yasuda K., Ohmura R.

Fluid Phase Equilibria (Fluid Phase Equilibria) 517 2020.08

ISSN 03783812

This paper provides the review focusing on the clathrate hydrates at the temperatures below the freezing point of water. The three main topics of the review are the chemical thermodynamics, naturally-occurring hydrates and novel industrial applications utilizing hydrates. Fundamental phase equilibria in the hydrate forming systems at the temperatures below the freezing point of water are first reviewed. The effects of water-soluble compound on the hydrate phase equilibria are extensively discussed based on the experimental data reported in the literature and the newly obtained experimental data on the solid ice + sodium chloride aqueous solution + carbon dioxide hydrate + carbon dioxide gas four-phase equilibria that were measured in the present study. Natural occurrence of hydrates is discussed by comparing the thermodynamic conditions in the planets and satellites with the relevant hydrate phase equilibrium data. The naturally-occurring hydrates would exist in the following planets and satellites; Mars and Titan. The storage of natural gas in the form of the hydrate has been well investigated in the past two decades. CO2 hydrate can be used as the fire-fighting agent and the solid carbonated foods. The refrigeration and engine utilizing hydrates as the working media may be the challenging technologies having the prospects in terms of the efficiency, environment friendliness and the safety.

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Molecular dynamics simulations of interfacial properties of the CO<inf>2</inf>-water and CO<inf>2</inf>-CH<inf>4</inf>-water systems

Naeiji P., Woo T.K., Alavi S., Ohmura R.

Journal of Chemical Physics (Journal of Chemical Physics) 153 ( 4 ) 2020.07

ISSN 00219606

Molecular dynamics simulations were performed to study the interfacial behavior of the pure carbon dioxide-water system and a binary 40:60 mol. % gas mixture of (carbon dioxide + methane)-water at the temperatures of 275.15 K and 298.15 K and pressures near 4 MPa for CO2 and up to 10 MPa for methane. The simulations are used to study the dynamic equilibrium of the gases at the water-gas interface, to determine the z-density profiles for the gases and water, and calculate the interfacial tension γ under the different temperature/pressure conditions close to those of the formation of clathrate hydrates of these gases. At the same hydrostatic gas phase pressure, the CO2-water interface has a lower interfacial tension than the CH4-water interface. A greater number of CO2 molecules, as much as three times more than methane at the same pressure, were adsorbed at the interfacial layer, which reflects the stronger electrostatic quadrupolar and van der Waals interactions between CO2 and water molecules at the interface. The water surfaces are covered by less than a monolayer of gas even when the pressure of the system goes near the saturation pressure of CO2. The surface adsorbed molecules are in dynamic equilibrium with the bulk gas and with exchange between the gas and interface regions occurring repeatedly within the timescale of the simulations. The effects of the changes in the CO2-water interfacial tension with external temperature and pressure conditions on the formation of the clathrate hydrates and other CO2 capture and sequestration processes are discussed.

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Thermophysical Property Measurements of Tetrabutylphosphonium Oxalate (TBPOx) Ionic Semiclathrate Hydrate as a Media for the Thermal Energy Storage System

Miyamoto T., Koyama R., Kurokawa N., Hotta A., Alavi S., Ohmura R.

Frontiers in Chemistry (Frontiers in Chemistry) 8 2020.07

With increasing global power demand, thermal energy storage technology could play a role ensuring a sustainable energy supply in power generation from renewable energy sources and power demand concentration. Hydrates have high potential as phase change materials (PCMs) for the use as a thermal energy storage medium. To develop thermal energy storage technology using a hydrate-based material, further investigation of thermophysical properties and the selection of a suitable hydrate are required. Tetrabutylphosphonium oxalate (TBPOx) ionic semiclathrate hydrate contains oxalic acid in salt form, as a guest compound, which is classified as carboxylic acid group with low environmental impact. In the present study, the phase equilibrium temperature and the dissociation heat of TBPOx hydrate were measured. The highest equilibrium temperature of the solid hydrate formed was 9.4°C at the mass fraction 0.35 of TBPOx in aqueous solution. The largest dissociation heat was 186.0 ± 0.5 kJ·kg−1 at the mass fraction of 0.35. Comparing with other PCMs with close phase equilibrium temperatures, TBPOx hydrate is superior in safety and sustainability. These results indicate that TBPOx hydrate would be suitable as the thermal storage medium for the general air conditioning systems.

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Improving thermal efficiency of hydrate-based heat engine generating renewable energy from low-grade heat sources using a crystal engineering approach

Koyama R., Chen L.J., Alavi S., Ohmura R.

Energy (Energy) 198 2020.05

ISSN 03605442

The development of the eco-friendly technology generating energy will be a gradual requirement all over the world to replace thermal power releasing CO2 and nuclear power for which the wastes are disposed of with great difficultly. The hydrate-heat engine is a new cycle obtaining mechanical work from temperature differences that normally cannot generate energy, for example, heat differences between the top and bottom seawater. Although the hydrate cycle is a more sustainable power generation system than typically used Rankine cycle from the aspect of using environmental harmless working media, this new cycle has an issue as the low thermal efficiency. To increase the thermal efficiency, the performance of the hydrate-based heat engine utilizing structure II and H hydrates is theoretically evaluated for various models of low-grade heat sources. The results showed that the structure II and H hydrates formed by adding large guest molecule compounds to a second small guest gas system were effective in improving thermal efficiency. Especially, the double hydrate with Kr and cyclopentane enable the hydrate cycle to perform as efficiently as Rankine cycle, having the thermal efficiency around 3.0%, for the ocean thermal energy conversion in the temperature range from 282 K to 293 K.

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Equilibrium temperature and dissociation heat of tetrabutylphosphonium acrylate (TBPAc) ionic semi-clathrate hydrate as a medium for the hydrate-based thermal energy storage system

Koyama R., Hotta A., Ohmura R.

Journal of Chemical Thermodynamics (Journal of Chemical Thermodynamics) 144 2020.05

ISSN 00219614

The hydrate-based thermal energy storage system is one of the most effective supplemental technologies to stabilize the energy supply for renewable energies. The system is expected to solve the global energy-management issues related to energy-demand increase and energy supply chain. In fact, this eco-friendly technology requires prospective hydrate candidates for the thermal energy storage media, followed by the extensive investigation of the thermophysical properties of the selected hydrates. In this study, to satisfy these requirements, the equilibrium temperature and the dissociation heat of tetrabutylphosphonium acrylate (TBPAc) ionic semi-clathrate hydrate were studied. It was found that the highest equilibrium temperature was 14.4 °C at the mass fractions from 0.37 to 0.40. It was also found that the largest dissociation heat was (210.4 ± 5.3) kJ kg−1 at the mass fraction 0.39. These values indicate that TBPAc hydrate could be a new promising thermal-storage medium for the general or data-centre air-conditioning systems. The experimental results of this study also revealed an underlying tendency between the thermophysical properties of the tetrabutylphosphonium (TBP) + carboxylate salt hydrates and the molar mass of the guest anion in salt.

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Interfacial tension between decane saturated with methane and water from 283.2 K to 298.2 K under pressures upto 10 MPa

Kodera M., Watanabe K., Lassiège M., Alavi S., Ohmura R.

Journal of Industrial and Engineering Chemistry (Journal of Industrial and Engineering Chemistry) 81 360 - 366 2020.01

ISSN 1226086X

Interfacial tension is one of the most important physical properties for high-precision simulations to develop the methods of preventing plugging of pipelines in the oil and natural gas industry. This paper reports experimental data with the pendant drop method for the interfacial tension of a decane + methane + water system at temperatures between 278.2 K to 298.2 K and pressures up to 10 MPa. The data show that in this temperature range the interfacial tension in the decane + methane + water system decreases almost linearly with increasing temperature. The results also show that by increasing the pressure of methane, the interfacial tension decreases from 53.98 mN m−1 to 50.23 mN m−1 at 283.2 K and 52.23 mN m−1 to 49.74 mN m−1 at 288.2 K. The nature of the methane pressure dependence of the interfacial tension changes for pressures above around 2.00 MPa. The interfacial tension decreases with the pressure up to 2.00 MPa, but has no pressure dependence above 2.00 MPa. It may be inferred that the decane/water interface is saturated with methane at pressures around 2.00 MPa and at higher pressure the interfacial tension is no longer affected by the presence of methane.

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Synthesis of Methane Hydrate from Ice Powder Accelerated by Doping Ethanol into Methane Gas

Chen Y., Chu L., Chu C., Ohmura R., Chen L.

Scientific Reports (Scientific Reports) 9 ( 1 ) 2019.12

Clathrate hydrate is considered to be a potential medium for gas storage and transportation. Slow kinetics of hydrate formation is a hindrance to the commercialized process development of such applications. The kinetics of methane hydrate formation from the reaction of ice powder and methane gas doped with/without saturated ethanol vapor at constant pressure of 16.55 ± 0.20 MPa and constant temperature ranging from −15 to −1.0 °C were investigated. The methane hydrate formation can be dramatically accelerated by simply doping ethanol into methane gas with ultralow ethanol concentration (<94 ppm by mole fraction) in the gas phase. For ethanol-doped system 80.1% of ice powder were converted into methane hydrate after a reaction time of 4 h, while only 26.6% of ice powder was converted into methane hydrate after a reaction time of 24 h when pure methane gas was used. Furthermore, this trace amount of ethanol could also substantially suppress the self-preservation effect to enhance the dissociation rate of methane hydrate (operated at 1 atm and temperatures below the ice melting point). In other words, a trace amount of ethanol doped in methane gas can act as a kinetic promoter for both the methane hydrate formation and dissociation.

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Diversity in Crystal Growth Dynamics and Crystal Morphology of Structure-H Hydrate

Matsuura R., Horii S., Alavi S., Ohmura R.

Crystal Growth and Design (Crystal Growth and Design) 19 ( 11 ) 6398 - 6404 2019.11

ISSN 15287483

This paper demonstrates the diversity in crystal growth dynamics and crystal morphology of structure-H hydrate formed with methane and methylcyclohexane (MCH) correlated to the driving force. ΔTsub, which is the difference between the experimental temperature of the crystal growth and the phase equilibrium temperature, was used as an index of the driving force. At ΔTsub = 1.6 and 3.2 K, hydrate crystals were initially formed at the water/MCH interface and grew into the hydrate film covering the interface. After the entire interface was covered by the hydrate film, the hydrate growth stopped. The shape of individual hydrate crystals was polygonal. The size of hydrate crystals was smaller with increasing ΔTsub. At ΔTsub = 5.3 K, the first hydrate crystals were observed at the water/MCH interface and crystals grew not only along the interface but also toward the interior of MCH phase, even after the water/MCH interface was completely covered by the hydrate film. The dendritic hydrate crystals were observed at the interface at ΔTsub = 5.3 K. The implications of these observations on crystal morphology on determining the conditions for methane capture for the purpose of storage and transportation are discussed.

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Thermophysical properties of trimethylolethane (TME) hydrate as phase change material for cooling lithium-ion battery in electric vehicle

Koyama R., Arai Y., Yamauchi Y., Takeya S., Endo F., Hotta A., Ohmura R.

Journal of Power Sources (Journal of Power Sources) 427 70 - 76 2019.07

ISSN 03787753

Management for the temperature increase of lithium-ion batteries in electric vehicles (EV) is required for safety and energy efficiency. As a cooling medium for lithium-ion batteries, one suitable candidate is trimethylolethane (TME) hydrate, which may be utilized as a phase change material (PCM). This hydrate has a large dissociation heat and will form/dissociate at approximately 30 °C under atmospheric pressure conditions. A cooling system which uses TME hydrate can have a high performance with regards to the efficiency and the stability of heat transfer process. However, in previous studies, the equilibrium temperature and the dissociation heat of TME hydrate have been reported only for a TME mass fraction of 0.625. Since TME hydrate forms in an aqueous solution, it is necessary to know how these thermophysical properties change for a range of TME mass fractions. Therefore, in this study, the equilibrium temperatures and the dissociation heats were measured respectively by the visual observation method and differential scanning calorimetry measurements for TME mass fraction range from 0.20 to 0.80. The highest equilibrium temperature was 29.6 °C at the mass fraction of 0.60. For the cooling system, the largest dissociation heat was 190.1 kJ kg−1, also at the mass fraction of 0.60.

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Phase equilibrium for clathrate hydrates formed with difluoromethane and N-methylpiperidine for hydrate-refrigeration system

Kondo Y., Murayama K., Ruiz A., Takeya S., Nemoto K., Ohmura R.

Renewable Energy and Power Quality Journal (Renewable Energy and Power Quality Journal) 17 114 - 117 2019.07

This paper reports the pressure-temperature conditions for the three-phase aqueous liquid + hydrate + vapor equilibrium in the hydrate formed with water, difluoromethane and methylpiperdine as large molecule guest compound (LMGC). The aim of the study is to obtain a hydrate formed in mild pressure-temperature conditions which could be applied to various technologies. To measure the pressure-temperature phase equilibrium, isochoric method[1] was used. The pressure and temperature ranges of the present measurements are from 61.9 to 104.2 kPa and from 259.3 to 272.2 K. Obtained results were comparatively mild conditions than the phase equilibrium p-T condition of the structure I hydrates formed with water + difluoromethane. To alleviate the phase equilibrium condition, the LMGCs showed its significance through this study. In addition, the cage structure of formed hydrates was measured by powder X-ray diffraction measurements. The hydrate samples were made using the difluoromethane and N-methylpiperidine. The measurement results indicated the cage structure of hydrate as structure H. Thus, the molecular size of difluoromethane was confirmed as the suitable size for the small cages of structure H.

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Theoretical performance analysis of hydrate-based refrigeration system

Matsuura R., Watanabe K., Yamauchi Y., Sato H., Ohmura R.

Renewable Energy and Power Quality Journal (Renewable Energy and Power Quality Journal) 17 118 - 122 2019.07

This paper reports theoretical performance analysis of the hydrate-based refrigeration system. The hydrate-based refrigerator transfers thermal energy through the cycle of following processes: adiabatic compression of guest compounds and water, hydrate formation, adiabatic expansion of hydrates, hydrate dissociation. The theoretical analyses and COP calculations were performed in the each of the following hydrate-forming systems: HFC-32+cyclopentane(CP) +water, Kr+CP+water, and HFC-41+CP+water system. Practical utility of hydrate-based refrigerator is discussed based on the comparison with the Carnot cycle.

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Thermophysical property measurements on tetrabutylphosphonium sulfate ionic semiclathrate hydrate consisting of the bivalent anion

Arai Y., Koyama R., Endo F., Hotta A., Ohmura R.

Journal of Chemical Thermodynamics (Journal of Chemical Thermodynamics) 131 330 - 335 2019.04

ISSN 00219614

To develop the “hydrate thermal energy storage technology” it is desired to reveal the mechanism of the thermophysical property manifestation on ionic semiclathrate hydrate. The influence of valence on thermophysical properties has not been investigated so far. In the present study, the phase equilibrium temperatures and the dissociation heats of tetrabutylphosphonium sulfate ((TBP)2SO4) ionic semiclathrate hydrate were experimentally studied. (TBP)2SO4 hydrate consists of the bivalent anion, SO42−. The highest phase equilibrium temperature was 6.5 °C at the mass fraction range from 0.363 to 0.384. The largest dissociation heat was (168.8 ± 2.4) kJ·kg−1 at the mass fraction 0.374. These values of the phase equilibrium temperature and the dissociation heat were respectively lower and smaller than those of the ionic semiclathrate hydrates with the monovalent anion. As a new choice for thermal energy storage medium, (TBP)2SO4 hydrate would be suitable to the automotive air conditioner and the cold chain for blood or perishable foods.

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Interfacial properties of hydrocarbon/water systems predicted by molecular dynamic simulations

Naeiji P., Woo T.K., Alavi S., Varaminian F., Ohmura R.

Journal of Chemical Physics (Journal of Chemical Physics) 150 ( 11 ) 2019.03

ISSN 00219606

The presence of small hydrocarbons is known to reduce the interfacial tension of the gas-water interface, and this phenomenon can affect the formation of the clathrate hydrates of these gases. In this work, the interfacial behavior of the pure methane-, ethane-, and propane-water, and the ternary 90:7:3 mol. % gas mixture of (methane + ethane + propane)-water were studied with molecular dynamics simulations. The interfacial tension, γ, and z-density profiles for the gases and water from simulations of the gas-water systems were determined at the temperatures of 275.15 and 298.15 K, and pressures up to 10 MPa for methane and up to near the experimental saturation pressures of ethane and propane. The goal is to accurately calculate the interfacial tension for the hydrocarbon/water systems and to analyze the molecular behaviors at the interfaces which lead to the observed trends. At the same hydrostatic gas phase pressure, propane, ethane, and methane reduce the gas-water interfacial tension in that order. The local density of the gas molecules at the interface is enhanced relative to the bulk gas, and it was determined that about 13%-20%, 33%-40%, and 54%-59% of the gas molecules in the simulation congregated at the interfaces for the CH 4 -, C 2 H 6 -, and C 3 H 8 -water systems, respectively, at the different simulated hydrostatic pressure ranges. For all gases in the pressure range studied, a complete monolayer of gas had not formed at the water interface. Furthermore, a dynamic equilibrium with fast exchange between molecules at the interface and in the gas phase was observed. For the gas mixture, deviations were observed between total calculated interfacial tension, γ mix , and the "ideal mixture" value, ςx i γ i,pure , calculated from the interfacial tensions of the pure gases, where x i is the mole fraction of each substance in the simulation. Some possible implications of the results on the mechanism of clathrate hydrate formation are discussed.

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Crystal Growth of Clathrate Hydrate with Methane plus Partially Water Soluble Large-Molecule Guest Compound

Ozawa K., Ohmura R.

Crystal Growth and Design (Crystal Growth and Design) 19 ( 3 ) 1689 - 1694 2019.03

ISSN 15287483

This paper reports the visual observations of the formation and growth of clathrate hydrate formed with methane plus a partially water soluble guest, tetrahydropyran (THP). THP is known to form a structure II hydrate with methane. The crystal growth dynamics and crystal morphology changed depending on T sub T eq - T ex , where T eq is the equilibrium temperature and T ex is the experimental temperature. At T sub ≥ 12 K, the hydrate crystals initially formed at the water-THP interface and then grew to form a hydrate film. After the hydrate film was formed, the hydrate formation stopped. At T sub < 12 K, the hydrate crystals that formed at the water-THP interface detached from the interface. The detachment of the hydrate crystals led to the maintenance of the interface and continual hydrate formation. These crystal growth dynamics may be ascribed to the reduced water-THP interfacial tension and the resulting enhancement of the wettability of hydrate with water in comparison with those in the system without THP.

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Continuous separation of CO<inf>2</inf> from H<inf>2</inf> + CO<inf>2</inf> gas mixture utilizing clathrate hydrate for integrated gasification combined cycle power plants

Horii S., Ohmura R.

2018 8th International Conference on Power and Energy Systems, ICPES 2018 (2018 8th International Conference on Power and Energy Systems, ICPES 2018) 212 - 216 2019.01

In this study, the CO2 continuous separation experiments were performed in the system of H2 + CO2 + H2O and H2 + CO2 + tetra-n-butylammonium bromide (TBAB) + H2O for TBAB mass fraction, wTBAB of 0 (the water system), 0.05, 0.10, 0.32. The time evolutions of compositions in the gas phase and the hydrate slurry were measured. The H2 compositions in the gas phase for wTBAB of 0, 0.05, and 0.10 reached steady state at 0.87, 0.81, and 0.78 while the CO2 compositions in the hydrate slurry were 1.00, 0.82, 0.79, respectively. It is shown that the experiments succeed in continuously separating CO2 with structure I hydrate and ionic semiclathrate hydrate. On the other hand, the hydrate transportation problem in separation process occurred for wTBAB = 0.32. For wTBAB = 0, the highest values of H2 compositions in the gas phase and CO2 compositions in hydrate slurry were obtained. The concentration of captured CO2 for wTBAB = 0 was comparable to that obtained by multistage process in hydrate-based gas separation or chemical absorption used in the demonstration project of integrated gasification combined cycle.

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Phase equilibrium condition measurements in carbon dioxide hydrate forming system coexisting with sodium chloride aqueous solutions

Nakane R., Gima E., Ohmura R., Senaha I., Yasuda K.

Journal of Chemical Thermodynamics (Journal of Chemical Thermodynamics) 130 192 - 197 2019.01

ISSN 00219614

Three phase equilibrium conditions of (sodium chloride aqueous solution + carbon dioxide hydrate + vapour carbon dioxide) were measured to establish seawater desalination technology using clathrate hydrates. The three phase equilibrium condition measurements were performed at temperatures between 271.85 K and 279.05 K, and at pressures between 1.283 MPa and 3.617 MPa. The concentrations of sodium chloride aqueous solution were 0.0350, 0.0700, 0.1000, and 0.1050 in mass fraction. It was found that the equilibrium temperature difference between pure water system and each sodium chloride concentration system at the same pressure was hardly influenced by the pressure level. In addition, it was found that the equilibrium temperature depression of carbon dioxide hydrate by the addition of sodium chloride is smaller than that of ice and cyclopentane hydrate especially at the high concentration of sodium chloride.

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Stability and characterization of the structure II binary clathrate hydrate of the refrigerant: Trans-1,3,3,3-tetrafluoropropene + methane

Nemoto K., Ikeda T., Mori H., Alavi S., Takeya S., Ohmura R.

New Journal of Chemistry (New Journal of Chemistry) 43 ( 33 ) 13068 - 13074 2019

ISSN 11440546

We report the phase diagram and structure of the binary clathrate hydrate (abbreviated as hydrate) of methane + trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) guest molecules by phase equilibrium measurements, powder X-ray diffraction measurements, and molecular dynamics simulations. The four-phase (methane-rich gas + water + HFO-1234ze(E) liquid + solid clathrate hydrate) equilibrium data in the system were measured in the temperature range of 274.3 K to 280.2 K. At temperatures from 274.3 K to 276.6 K, the phase equilibrium pressures of the binary hydrate were lower, by a maximum of 0.27 MPa, than those in a pure methane structure I clathrate hydrate system three phase equilibrium line. This indicates that the hydrate formed from the binary mixture was different from a simple methane hydrate. Powder X-ray diffraction measurements were performed on the binary hydrate sample prepared at 274.3 K and pressures from 2.65 to 2.94 MPa. The X-ray diffraction measurements revealed that a structure II hydrate was formed in the system. This is somewhat surprising as the longest molecular dimension of HFO-1234ze(E) is similar to that of 2-methylbutane that forms a structure H hydrate. To clarify some of the aspects of the behavior of the binary hydrate, molecular dynamics simulations were performed. These calculations show that the HFO-1234ze(E) molecules do not form hydrogen bonds with the cage water molecules but are closely interacting with the cage water molecules via electrostatic and van der Waals interactions.

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Effect of Nonspherical Encapsulated Guests on the Volumetric Behavior of Structure H Clathrate Hydrates

Arai Y., Takeya S., Alavi S., Yamauchi Y., Ohmura R.

Journal of Physical Chemistry C (Journal of Physical Chemistry C) 122 ( 48 ) 27631 - 27639 2018.12

ISSN 19327447

Since its first discovery, technologies utilizing the structure H (sH) clathrate hydrates have been proposed. To develop the technology, understanding the mechanism of thermophysical property manifestation would be of fundamental importance. It is reported in the literature that the molecular properties of guest molecules had a significant influence on the crystal structure and the resulting thermophysical properties of the sH hydrate. In the present study, the effect of linear N2 help-gas molecule on the crystal structure was experimentally and computationally investigated to focus on the shape of the guest molecule in the sH binary clathrate with neohexane. Powder X-ray diffraction (PXRD) measurements were performed in temperatures from 93 to 183 K. The lattice constant values on a and c axes, the cage occupancies of small 512 and 435663 cages, and guest distributions in the host cages were determined. Parrinello-Rahman molecular dynamics (MD) simulations were performed on the sH clathrate hydrate phase. The simulated values of the lattice constants indicated the same tendency as the experimental results. The MD simulations provided detailed descriptions of the molecular motions of guest molecules. On the basis of these results, the influence of a small guest molecule on the crystal structure of sH hydrate is discussed.

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Phase equilibrium for argon clathrate hydrate at the temperatures from 197.6 K to 274.1 K

Nagashima H., Nemoto K., Ohmura R.

Journal of Chemical Thermodynamics (Journal of Chemical Thermodynamics) 127 86 - 91 2018.12

ISSN 00219614

The phase equilibrium conditions of clathrate hydrate of argon were measured by the isochoric procedure at the temperatures from 197.6 K to 274.1 K. Argon hydrate would have industrial applications including a working medium of the hydrate-based heat pump systems as well as influence the analysis of the past climate change on the Earth. Nevertheless, the equilibrium conditions of argon hydrate were limited in the literatures and not reported below the temperature 264 K. The lowest and the highest measured equilibrium pressure is the pressure 0.825 MPa at the temperature 197.6 K and the pressure 9.881 MPa at the temperature 274.1 K. The equilibrium pressure increases with an increase in temperature. The reliability of the measured equilibrium conditions is supported by the internal consistency of those and the coincidence of the experimentally determined quadruple point (vapor + hydrate + ice + aqueous phases in equilibrium) temperature with the water freezing temperature theoretically predicted. The discussion is given on the comparison of the equilibrium data measured in this study and those reported in the literature.

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Thermodynamic Simulation for Continuous Formation of Ozone Hydrate

Watanabe K., Nagashima H., Nakamura R., Ohmura R.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 6 ( 9 ) 11624 - 11632 2018.09

O3 concentration in O3-containing clathrate hydrate formed by a continuous process is predicted using the thermodynamic simulation in which the hydrate-forming process is assumed to be a series of numerous equilibrium states each slightly deviating from the preceding state. The thermodynamic simulation was originally developed for natural gas hydrate. In this study, the simulation was modified to take account of O3 self-decomposition. The O3 decomposition rate was experimentally measured in the (O3 + O2 + CO2) system to be used for the material balance calculation model. The phase-equilibrium calculation model used in this study was validated by comparison of the experimental O3 concentration in hydrate to that calculated. The thermodynamic simulation indicated that the O3 concentration in hydrate increased with an increase in the fraction of the gas discharged from the reactor. The higher rate of hydrate formation increased the O3 concentration in hydrate asymptotically. This study revealed that the O3 mass concentration in hydrate formed in a continuous process was the order of percent, which was a hundred times greater than that in the other O3 storage technologies such as ozonated ice and ozonated water.

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Continuous separation of CO<inf>2</inf> from a H<inf>2</inf> + CO<inf>2</inf> gas mixture using clathrate hydrate

Horii S., Ohmura R.

Applied Energy (Applied Energy) 225 78 - 84 2018.09

ISSN 03062619

CO2 capture using clathrate hydrates is an environmentally friendly separation technology. When considering operational efficiency, it is desirable to operate the separation process continuously. In this experimental study, the continuous separation of CO2 from a model fuel gas was performed for H2 + CO2 + H2O and H2 + CO2 + tetra-n-butylammonium bromide (TBAB) + H2O systems with TBAB mass fractions of wTBAB = 0, 0.05, 0.10, and 0.32. Measurements were taken to track the time evolution of compositions of the gas phase and hydrate slurry. After between 37 and 48 h from the start of the experiment, H2 compositions in the gas phase reached steady state values of 0.87, 0.81, and 0.78 for wTBAB values of 0, 0.05, and 0.10, respectively. For the same conditions, CO2 compositions in the hydrate slurry reached steady state values of 1.00, 0.82, and 0.79, respectively. In carrying out this work we have shown that it is possible to successfully separate CO2 using structure I hydrates and ionic semiclathrate hydrates, on a continuous basis. There is the caveat, however, that for wTBAB = 0.32 a continuous separation process is not possible. The split fraction of CO2 we attained were 0.76, 0.64, and 0.62 for wTBAB values of 0, 0.05, and 0.10, respectively. The water system (wTBAB = 0) exhibited the highest H2 compositions in the gas phase, highest CO2 compositions in the hydrate slurry, and highest split fraction of CO2. Although short-term operation, specifically 18 h, is possible with wTBAB = 0, continuous hydrate formation cannot be implemented. The concentration of captured CO2 for wTBAB = 0 was comparable to that obtained from hydrate-based gas separation in multistage processes or chemical absorption.

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Distortion of the Large Cages Encapsulating Cyclic Molecules and Empty Small Cages of Structure II Clathrate Hydrates

Takeya S., Alavi S., Hashimoto S., Yasuda K., Yamauchi Y., Ohmura R.

Journal of Physical Chemistry C (Journal of Physical Chemistry C) 122 ( 31 ) 18134 - 18141 2018.08

ISSN 19327447

Understandings of structure-based properties of porous materials, such as gas storage and gas separation performance, are important. Here, the crystal structures of the canonical structure II (sII) clathrate hydrates encapsulating cyclic molecules (tetrahydrofuran, cyclopentane, furan, and tetrahydropyran) are studied. To understand the effect of guest molecules on the host water framework, we performed powder X-ray diffraction measurements where the hydrate structures and guest distribution within 51264 cages were obtained by the direct-space technique followed by the Rietveld refinement. It was shown that the sizes of the 512 and 51264 cages of sII hydrates expand, as its unit-cell size is enlarged by the guest. In this process, it is revealed that the shape of 51264 cages with larger guest molecules became more spherical and volume ratio of empty small 512 cages in the unit cell decreases. Our findings from crystallographic point of view may give insights into better understanding of the thermodynamic stability and higher gas storage capacity of binary clathrate hydrates.

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Thermophysical property measurements of tetrabutylphosphonium acetate (TBPAce) ionic semiclathrate hydrate as thermal energy storage medium for general air conditioning systems

Arai Yuta, Yamauchi Yuji, Tokutomi Hiroki, Endo Fuyuaki, Hotta Atsushi, Alavi Saman, Ohmura Ryo

International Journal of Refrigeration 88 102 - 107 2018.04

ISSN 0140-7007

This paper reports the experimental study on measuring the phase equilibrium temperatures and the dissociation heats of ionic semiclathrate hydrate formed with tetrabutylphosphonium acetate (TBPAce) under atmospheric pressure. The phase equilibrium temperature and the dissociation heat measurements were performed in the range of the mass fraction of TBPAce aqueous solution from 0.10 to 0.42. The highest phase equilibrium temperature was 11.0 °C at the mass fraction range from 0.35 to 0.39. The largest dissociation heat of pure TBPAce hydrate was 192.0 kJ kg^–1 at the mass fraction 0.36. The obtained results indicate that TBPAce hydrate would be suitable for a new thermal energy storage medium for general air conditioning systems.

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Interfacial tension measurements in the (CO₂ + H₂) gas mixture and water system at temperatures from 271.2 K to 280.2 K and pressures up to 7.0 MPa

Fukuzawa Kazuki, Watanabe Kosuke, Yasuda Keita, Ohmura Ryo

Journal of Chemical Thermodynamics 119 20 - 25 2018.04

ISSN 0021-9614

This paper reports the experimental values of the interfacial tension between a gas mixture (CO₂ + H₂) and water measured with the pendant drop method. The measurements were conducted for temperatures from 271.2 K to 280.2 K and pressures up to 7.0 MPa, at increments of 1 MPa. These temperature-pressure ranges were nearly close to the (CO₂ + H₂) hydrate-stability-zone but each result is obtained without existence of any hydrate. The temperature dependency of the interfacial tension in this system could not be observed, but the interfacial tension decreased almost linearly with increasing pressure, indicating that the observed decrease was caused by an increase in adsorption of the gas phase onto the liquid water with pressure. The gradient of the interfacial tension, with respect to the pressure, was confirmed to be determined by the gas phase composition. The interaction between gases has a marginal influence on the interfacial tension between the (CO₂ + H₂) gas mixture and water.

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Guest-guest and guest-host interactions in ethanol, propan-1-ol, and propan-2-ol clathrate hydrate forming systems

Yasuda K., Ohmura R., Sum A.K.

New Journal of Chemistry (New Journal of Chemistry) 42 ( 9 ) 7364 - 7370 2018

ISSN 11440546

In the present study, Raman spectroscopic measurements were performed using clathrate hydrate samples composed of ethanol, propan-1-ol, or propan-2-ol + deuterated methane + deuterium oxide. The temperature of the samples was stepwise increased from 93 K to 263 K in steps of 10 K or 20 K to decompose the clathrate hydrate samples during the measurements. The Raman spectra of the alcohols + deuterated methane hydrate sample in the C-H symmetric vibration region were similar to that of pure vapor alcohols, which indicates the weak guest alcohol-host water interaction although alcohols are hydrophilic compounds. In the propan-2-ol + deuterated methane + deuterium oxide system, the formation of two compounds having different composition from structure II propan-2-ol + deuterated methane clathrate hydrate was observed.

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Solubility of Nitrogen Gas in Aqueous Solution of Tetra-n-Butylammonium Bromide

Muromachi, Sanehiro, Miyamoto, Hiroyuki, Ohmura, Ryo

INTERNATIONAL JOURNAL OF THERMOPHYSICS 38 ( 12 ) 20 - 25 2017.12

Research paper (scientific journal), ISSN 0195-928X

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Preservation of carbon dioxide clathrate hydrate in the presence of fructose or glucose and absence of sugars under freezer conditions

Nagashima, Hironori D., Alavi, Saman, Ohmura, Ryo

JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY 54 332 - 340 2017.10

Research paper (scientific journal), ISSN 1226-086X

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Thermodynamic Properties of Ionic Semiclathrate Hydrate Formed with Tetrabutylammonium Propionate

Yamauchi, Yuji, Yamasaki, Tatsuro, Endo, Fuyuaki, Hotta, Atsushi, Ohmura, Ryo

CHEMICAL ENGINEERING & TECHNOLOGY 40 ( 10 ) 1810 - 1816 2017.10

Research paper (scientific journal), ISSN 0930-7516

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Formation, growth and sintering of CO2 hydrate crystals in liquid water with continuous CO2 supply: Implication for subsurface CO2 sequestration

Oya, Shun, Aifaa, Muhammad, Ohmura, Ryo

INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL 63 386 - 391 2017.08

Research paper (scientific journal), ISSN 1750-5836

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Interfacial tension between (methane + ethane + propane) gas mixture and water from 283.2 K to 298.2 K under up to 10 MPa

Hayama Hiroaki, Fukuzawa Kazuki, Yasuda Keita, Ohmura Ryo

Journal of Chemical Thermodynamics 108 71 - 75 2017.05

ISSN 0021-9614

This paper reports a study of the interfacial tension between natural gas (methane + ethane + propane gas mixture) and water. The composition of the (methane + ethane + propane) gas mixture was 89.95:7.05:3.00 and 95.0:3.5:1.5, in mole ratio. These measurements were performed using the pendant drop method at pressure and temperature conditions of up to 10 MPa and between 283.2 K and 298.2 K, respectively. These conditions were chosen to eliminate the possibility of clathrate hydrate formation. Interfacial tension in the (natural gas + water) system decreased with increasing pressure, but no temperature dependence was found for any of the at all conditions. The interfacial tension gradient with respect to pressure was found to depend on the composition of gas phase. The interfacial tension in a (natural gas + water) system was found to be smaller than that of a (methane + water) system.

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Phase equilibria for Kr hydrate formed with 2,2-dimethylbutane, methylcyclohexane and 1-methylpiperidine

Ohfuka Yugo, Fukushima Naruki, Chen Zheguang, Fukuda Masao, Takeya Satoshi, Ohmura Ryo

Journal of Chemical Thermodynamics 2017

ISSN 0021-9614

This paper reports the thermophysical properties of hydrates in the (krypton + 1-methylpiperidine, 2,2-dimethylbutane or methylcyclohexane + water) system. Phase equilibrium conditions were measured in the temperature ranges from 274.6. K to 297.3. K at the corresponding equilibrium pressures between 0.532. MPa and 6.246. MPa in the (krypton + 1-methylpiperidine + water) system. In the temperature ranges from 291.2. K to 297.0. K and 290.6. K to 296.8. K, the equilibrium pressure was between 4.035. MPa to 8.936. MPa and 3.993. MPa to 9.128. MPa, in the (krypton + 2,2-dimethylbutane + water) system and (krypton + methylcyclohexane + water) system, respectively. These results indicate that hydrates can be formed under the condition of lower temperature and pressure in the (krypton + 1-methylpiperidine + water) system than in the other two systems. The crystallographic structure of (krypton + 1-methylpiperidine) hydrate was thereby identified to be structure H at 183. K based on the Powder X-ray diffraction (PXRD) measurements. Dissociation heat of (krypton + 1-methylpiperidine) hydrate was estimated to be 73.5. kJ/mol, that is smaller than that of structure II hydrates containing krypton. These results support the potential for (krypton + 1-methylpiperidine) structure H hydrate to be utilized in hydrate-based technologies.

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Phase equilibrium condition measurements in the clathrate hydrate forming system of (propan-2-ol + carbon dioxide + water) at temperatures between 250.8 K and 265.7 K

Fukushima Naruki, Shiratori Satoshi, Makiya Takeshi, Murakami Takashi, Ohmura Ryo

Journal of Chemical Thermodynamics 115 114 - 118 2017

ISSN 0021-9614

The phase equilibrium conditions in the (propan-2-ol + carbon dioxide + water) system were measured. The measurements were performed using the batch, isochoric method at the temperatures between 250.8 K and 265.7 K. The equilibrium pressures were measured between 0.275 MPa and 0.995 MPa, and increased with increasing temperatures. Propan-2-ol is known as thermodynamic inhibitor for hydrate formation. However at the temperatures below 262 K, the equilibrium pressures in the (propan-2-ol + carbon dioxide + water) system are lower than those without propan-2-ol (carbon dioxide + water system). The measurements indicate the formation of the hydrates containing propan-2-ol and carbon dioxide in this system.

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Phase equilibrium condition measurements in methane clathrate hydrate forming system from 197.3 K to 238.7 K

Nagashima Hironori D., Ohmura Ryo

Journal of Chemical Thermodynamics 102 252 - 256 2016.11

ISSN 0021-9614

This paper reports three-phase (ice + vapor + clathrate hydrate) equilibrium conditions in methane + water system at temperatures between 197.3 K and 238.7 K. These equilibrium condition data could be applied for utilization of methane clathrate hydrate as a natural gas transportation medium, a working medium for heat pump/power generation cycles, and to further our understanding of the environments of planets and satellites. The equilibrium conditions were measured using the isochoric procedure. The measured equilibrium pressures are from 111.7 kPa at 197.3 K to 794.1 kPa at 238.7 K and increase with an increase in temperature. The internal consistency of the measured equilibrium data are examined by applying the Clausius-Clapeyron equation. Discussion is given on the comparison of the equilibrium data measured in this study to those reported in the literature.

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Phase equilibrium temperature and dissociation heat of ionic semiclathrate hydrate formed with tetrabutylammonium butyrate

Yamauchi Yuji, Arai Yuta, Yamasaki Tatsuro, Endo Fuyuaki, Hotta Atsushi, Ohmura Ryo

Fluid Phase Equilibria 2016.10

ISSN 0378-3812

This paper reports the phase equilibrium temperature and dissociation heat of ionic semiclathrate hydrate formed with tetrabutylammonium butyrate (TBABu). The temperature - composition phase diagram of the TBABu hydrate was determined in the mass fraction from 0.10 to 0.44. The highest equilibrium temperature of TBABu hydrate was 15.4 °C in the mass fraction range from 0.35 to 0.37. On the dissociation heat of DSC measurements, a single heat flow peak of TBABu hydrate excluding ice melting peak was observed at all the mass fraction systems. The largest dissociation heat was 184.9 ± 3.1 kJ/kg at the mass fraction 0.36. TBABu hydrate could potentially be used as a thermal energy storage material.

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Understanding decomposition and encapsulation energies of structure I and II clathrate hydrates

Alavi Saman, Ohmura Ryo

Journal of Chemical Physics 145 ( 15 ) 2016.10

ISSN 0021-9606

When compressed with water or ice under high pressure and low temperature conditions, some gases form solid gas hydrate inclusion compounds which have higher melting points than ice under those pressures. In this work, we study the balance of the guest-water and water-water interaction energies that lead to the formation of the clathrate hydrate phases. In particular, molecular dynamics simulations with accurate water potentials are used to study the energetics of the formation of structure I (sI) and II (sII) clathrate hydrates of methane, ethane, and propane. The dissociation enthalpy of the clathrate hydrate phases, the encapsulation enthalpy of methane, ethane, and propane guests in the corresponding phases, and the average bonding enthalpy of water molecules are calculated and compared with accurate calorimetric measurements and previous classical and quantum mechanical calculations, when available. The encapsulation energies of methane, ethane, and propane guests stabilize the small and large sI and sII hydrate cages, with the larger molecules giving larger encapsulation energies. The average water-water interactions are weakened in the sI and sII phases compared to ice. The relative magnitudes of the van der Waals potential energy in ice and the hydrate phases are similar, but in the ice phase, the electrostatic interactions are stronger. The stabilizing guest-water “hydrophobic” interactions compensate for the weaker water-water interactions and stabilize the hydrate phases. A number of common assumptions regarding the guest-cage water interactions are used in the van der Waals-Platteeuw statistical mechanical theory to predict the clathrate hydrate phase stability under different pressure-temperature conditions. The present calculations show that some of these assumptions may not accurately reflect the physical nature of the interactions between guest molecules and the lattice waters.

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Quadruple point determination in carbon dioxide hydrate forming system

Nema Yuki, Ohmura Ryo, Senaha Izuru, Yasuda Keita

Fluid Phase Equilibria 2016.10

ISSN 0378-3812

The quadruple point in carbon dioxide hydrate forming system, ice + water-rich liquid + hydrate + carbon dioxide-rich gas four-phase equilibrium condition, has been determined based on supercooled water-rich liquid + hydrate + carbon dioxide-rich gas and water-rich liquid + hydrate + carbon dioxide-rich gas three-phase equilibrium conditions measured in this study combined with ice + hydrate + carbon dioxide-rich gas three-phase equilibrium conditions reported in the literature (K. Yasuda, R. Ohmura, J. Chem. Eng. Data 53 (2008) 2182-2188). The intersection of the three types of the three-phase equilibrium conditions was used to determine the quadruple point. The three-phase equilibrium condition experiments were performed at temperatures between 269.45 K and 275.75 K, and at pressures between 0.825 MPa and 1.708 MPa. The determined . p-T condition at quadruple point was . T = 271.6 ± 0.2 K and . p = 1.04 ± 0.02 MPa. It was also observed that the freezing of supercooled water during some experimental runs performed below the quadruple point temperature, which causes sudden increase in both pressure and temperature.

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Surfactant Effects on Crystal Growth Dynamics and Crystal Morphology of Methane Hydrate Formed at Gas/Liquid Interface

Hayama Hiroaki, Mitarai Makoto, Mori Hiroyuki, Verrett Jonathan, Servio Phillip, Ohmura Ryo

Crystal Growth and Design 16 ( 10 ) 6084 - 6088 2016.10

ISSN 1528-7483

This paper presents visual observations aiming to clarify the underlying physics of surfactant effects on clathrate hydrate crystal growth at the interface between methane gas and water with surfactant. Sodium dodecyl sulfate (SDS), which is commonly used in industrial processes, was used in this study. Various SDS mass fractions from 0 to w_SDS = 100 ppm with a step of size 10 ppm were examined, where w_SDS represents the mass fraction of SDS aqueous solution. The crystal growth behavior and the crystal morphology of the methane hydrate at the interface varied depending on surfactant concentration and ΔT_sub. In systems with w_SDS ≤ 20 ppm, the nucleation occurred on the droplet surface (gas/liquid interface), then grew laterally, and finally covered the whole droplet surface. On the contrary, at w_SDS ≥ 30 ppm, the droplet shape was not maintained and enhanced hydrate crystal growth was observed compared to those systems with w_SDS ≤ 20 ppm. Individual hydrate crystals at w_SDS = 20 ppm were observed to be smaller than those in a pure water system at a given ΔT_sub, which is ascribed to the enhanced hydrate nucleation by the addition of SDS.

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Interfacial tension between (CO₂ + N₂) gas and tetrabutylammonium bromide aqueous solution

Akiba Hotaka, Ohmura Ryo

Journal of Chemical Thermodynamics 97 83 - 87 2016.06

ISSN 0021-9614

This paper reports experimental values of the interfacial tension between (CO₂ + N₂) gas and tetrabutylammonium bromide aqueous solution (TBAB_aq). The experiments were performed by the pendant drop method in conditions from P = (1.00 to 4.00) MPa, from T = (288.15 to 303.15) K and from w_TBAB = (0.10 to 0.40), where w_TBAB denotes the mass fraction of TBAB in the aqueous solution. The interfacial tension decreased with increasing w_TBAB and pressure. The depletion of the interfacial tension with increasing w_TBAB in the (CO₂ + N₂ + TBAB_aq) system was consistent with that in (CO₂ + TBAB_aq) system. The depletion ratio of the pressure gradient of the interfacial tension caused by the addition of TBAB in (CO₂ + N₂ + water) system was almost the same as that in (CO₂ + water) system. There might be little effect on the interfacial tension caused by the interaction between gases and tetrabutylammonium ions. The temperature dependence of γ was not observed as well as in the (CO₂ + TBAB_aq) system.

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Disorder of Hydrofluorocarbon Molecules Entrapped in the Water Cages of Structure i Clathrate Hydrate

Takeya Satoshi, Udachin Konstantin A., Moudrakovski Igor L., Ohmura Ryo, Ripmeester John A.

Chemistry - A European Journal 22 ( 22 ) 7567 - 7573 2016.05

ISSN 0947-6539

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Selective occupancy of methane by cage symmetry in TBAB ionic clathrate hydrate

Muromachi Sanehiro, Udachin Konstantin A., Alavi Saman, Ohmura Ryo, Ripmeester John A.

Chemical Communications 52 ( 32 ) 5621 - 5624 2016.04

ISSN 1359-7345

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Preface to special issue on gas hydrates and semiclathrate hydrates

Sum Amadeu K., Ohmura Ryo, de Loos Theo

Fluid Phase Equilibria 413 1 2016.04

ISSN 0378-3812

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Interfacial tension measurements in water-methane system at temperatures from 278.15 K to 298.15 K and pressures up to 10 MPa

Yasuda Keita, Mori Yasuhiko H., Ohmura Ryo

Fluid Phase Equilibria 413 170 - 175 2016.04

ISSN 0378-3812

This paper reports the measurements of the interfacial tension in a water-methane system at temperatures from 278.15 K to 298.15 K and pressures up to 10 MPa. The measurements using the pendant-drop method were performed at various pressures lower than or, at the highest, nearly equal to the hydrate/liquid/gas equilibrium pressure corresponding to each of the following prescribed temperatures: 278.15 K, 283.15 K, 288.15 K, 293.15 K and 298.15 K. The obtained data show that at each temperature the interfacial tension decreases almost linearly with the increasing pressure, indicating that the observed decrease in the interfacial tension results from the promotion of methane adsorption onto the interface with the increasing pressure.

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Crystal growth of ionic semiclathrate hydrate formed at interface between CO₂+N₂ gas mixture and tetrabutylammonium bromide aqueous solution

Hayama Hiroaki, Akiba Hotaka, Asami Yuki, Ohmura Ryo

Korean Journal of Chemical Engineering 1 - 6 2016.04

ISSN 0256-1115

This study reports a visual observation of the formation and growth of ionic semiclathrate hydrate on the surface of a Tetrabutylammonium bromide (TBAB) aqueous solution and CO₂+N₂ gas mixture. The composition of CO₂+N₂ gas mixture was 20: 80. The experimental temperature range was from 280 K to 290 K, under the pressures of 2.3MPa and 4.7MPa, at w_TBAB=0.10 and w_TBAB=0.40, where wTBAB denotes the mass fraction of TBAB in the aqueous solution. At w_TBAB=0.40, the hydrate crystals were initially observed to grow within the droplet, and followed by lateral growth at the droplet surface; but at w_TBAB=0.10, the hydrate crystals grew exclusively in the liquid phase and did not cover the droplet surface. Two types of different crystals with different sizes were clearly observed.

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Crystal growth of ionic semiclathrate hydrate formed at interface between CO2+N2 gas mixture and tetrabutylammonium bromide aqueous solution

Hiroaki Hayama , Hotaka Akiba , Yuki Asami , Ryo Ohmura Affiliated with Department of Mechanical Engineering, Keio University Email author Hiroaki Hayama , Hotaka Akiba , Yuki Asami , Ryo Ohmura Affiliated with Department of Mechanical Engineering, Keio University Email author Hiroaki Hayama, Hotaka Akiba, Yuki Asami, Ryo Ohmura

Korean Journal of Chemical Engineering (Springer) 2016.04

Research paper (scientific journal), Joint Work, Accepted

Influence of hydrate structure on continuous separation of coal bed methane gas: A thermodynamic simulation study

Thaneer Malai Narayanan, Ryo Ohmura

Journal of Natural Gas Science & Engineering 2016.03

Research paper (scientific journal), Joint Work, Accepted

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Selective occupancy of methane by cage symmetry in TBAB ionic clathrate hydrate

Sanehiro Muromachi, Konstantin A. Udachin, Saman Alavi, Ryo Ohmura and John A. Ripmeester

Chemical Communications 2016.03

Research paper (scientific journal), Joint Work, Accepted

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Theoretical performance analysis of hydrate-based heat engine system suitable for low-temperature driven power generation

Yugo Ofuka, Ryo Ohmura

Energy 101 27 - 33 2016.02

Research paper (scientific journal), Joint Work, Accepted

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Interfacial tension between CO2 + N2 Gas and Tetrabutylammonium Bromide Aqueous Solution

Hotaka Akiba, Ryo Ohmura

The Journal of Chemical Thermodynamics (Elsevier) 97 83 - 87 2016.01

Research paper (scientific journal), Joint Work, Accepted

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Preservation of carbon dioxide clathrate hydrate in the presence of trehalose under freezer conditions

Hironori D. Nagashima , Satoshi Takeya , Tsutomu Uchida, and Ryo Ohmura

Scientific Reports 6 19354 2016.01

Research paper (scientific journal), Joint Work, Accepted

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Surface tension between CO<inf>2</inf> gas and tetra-n-butylammonium bromide aqueous solution

Akiba Hotaka, Ohmura Ryo

Journal of Chemical Thermodynamics 92 72 - 75 2016.01

ISSN 0021-9614

This paper reports experimental values of the surface tension between CO<inf>2</inf> gas and tetra-n-butylammonium bromide (TBAB) aqueous solution measured by the pendant drop method. The experimental conditions were pressures from 1.00 MPa to 4.00 MPa, temperatures from 288.15 K to 303.15 K and w<inf>TBAB</inf> from 0.10 to 0.40, where w<inf>TBAB</inf> denotes the mass fraction of TBAB in the aqueous solution. These pressure-temperature-composition conditions partially fall into the stability zone of (CO<inf>2</inf> + TBAB) semiclathrate hydrate but all data were obtained without any hydrate in the system. Surface tension decreased with increasing w<inf>TBAB</inf> and pressure but temperature dependency was not observed. Compared to the air-TBAB aqueous solution system and CO<inf>2</inf>-water system, the values of the surface tension were smaller.

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Methane Hydrate Crystal Growth at the Gas/Liquid Interface in the Presence of Sodium Dodecyl Sulfate

Hayama Hiroaki, Mitarai Makoto, Mori Hiroyuki, Ohmura Ryo

Procedia Engineering 148 339 - 345 2016

ISSN 1877-7058

This study reports the visual observation made of the formation and growth of clathrate hydrate on the surface boundary of a Sodium Dodecyl Sulfate (SDS) aqueous solution droplet and surrounding methane gas. The experimental temperature range was from 276 K to 282 K, under the pressure of 7.8 MPa, at pure water, w_SDS = 10 ppm and w_SDS = 100 ppm, where w_SDS denotes the mass fraction of SDS in the aqueous solution. At pure water and w_SDS = 10 ppm, the hydrate crystals were initially observed at the droplet surface, and followed by lateral growth at the droplet surface. However, at w_SDS = 100 ppm, it was observed that hydrate growth behavior greatly changed compared to pure water system. At w_SDS = 100 ppm and ΔT_sub < 6.0 K, the structure of the droplet was not maintained and hydrate crystals grew horizontally on to the stage. We defined the subcooling, ΔT_sub, the difference between the system temperature and the equilibrium temperature of methane hydrate as driving force index for crystal growth. At w_SDS = 100 ppm and ΔT_sub ≥ 6.0 K, the hydrate grew perpendicularly to the stage. At w_SDS = 100 ppm and each ΔT_sub, the amount of hydrate produced increased compared to pure water system.

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Phase Transition of a StructureII Cubic Clathrate Hydrate to a Tetragonal Form

Takeya Satoshi, Fujihisa Hiroshi, Yamawaki Hiroshi, Gotoh Yoshito, Ohmura Ryo, Alavi Saman, Ripmeester John A.

Angewandte Chemie - International Edition 2016

ISSN 1433-7851

The crystal structure and phase transition of cubic structureII (sII) binary clathrate hydrates of methane (CH₄) and propanol are reported from powder X-ray diffraction measurements. The deformation of host water cages at the cubic-tetragonal phase transition of 2-propanol+CH₄ hydrate, but not 1-propanol+CH₄ hydrate, was observed below about 110K. It is shown that the deformation of the host water cages of 2-propanol+CH₄ hydrate can be explained by the restriction of the motion of 2-propanol within the 5¹²6⁴ host water cages. This result provides a low-temperature structure due to a temperature-induced symmetry-lowering transition of clathrate hydrate. This is the first example of a cubic structure of the common clathrate hydrate families at a fixed composition.

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The Measurement of Dissociation Heat and Equilibrium Temperature of Tetrabutylammonium Propionate Hydrate

Yamauchi Yuji, Yamasaki Tatsuro, Okoshi Ryusuke, Endo Fuyuaki, Hotta Atsushi, Ohmura Ryo

Procedia Engineering 148 333 - 338 2016

ISSN 1877-7058

This paper reports the results of an experimental study conducted to measure the thermodynamics properties of ionic semiclathrate hydrate formed with tetrabutylammonium propionate (TBAPr). The thermodynamic measurements were performed on the equilibrium temperature and on the dissociation heat of the hydrate in the range of the mass fraction of tetrabutylammonium propionate wTBAPr from 0.10 to 0.43. The highest equilibrium temperature of the TBAPr system was 17.5 °C at wTBAPr = 0.37. The largest dissociation heat of TBAPr system was 193 kJ/kg at wTBAPr = 0.37. These findings indicate that TBAPr hydrate is promising for application in cool energy storage material.

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Structure and Guest Dynamics in Binary Clathrate Hydrates of Tetrahydropyran with Carbon Dioxide/Methane

Thaneer Malai Narayanan, Kazuki Imasato, Satoshi Takeya, Saman Alavi, and Ryo Ohmura

The Journal of Physical Chemistry C 119 ( 46 ) 25738 - 25746 2015.10

Research paper (scientific journal), Joint Work, Accepted

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Interfacial Tension Measurements in Water-Methane System at Temperatures from 278.15 K to 298.15 K and Pressures up to 10 MPa

Keita Yasuda, Yasuhiko H. Mori, and Ryo Ohmura

Fluid Phase Equilibria 413 170 - 175 2015.10

Research paper (scientific journal), Joint Work, Accepted

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Experimental study on combustion of a methane hydrate sphere

Tomoki Yoshioka, Yuji Yamamoto, Takeshi Yokomori, Ryo Ohmura, Toshihisa Ueda

Experiments in Fluids 56 2015.09

Research paper (scientific journal), Joint Work, Accepted

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Phase equilibrium condition measurements in carbon dioxide clathrate hydrate forming system from 199.1 K to 247.1 K

Hironori D. Nagashima, Naruki Fukushima and Ryo Ohmura

Fluid Phase Equilibria 413 53 - 56 2015.09

Research paper (scientific journal), Joint Work, Accepted

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Thermal conductivity measurements of semiclathrate hydrates and aqueous solutions of tetrabutylammonium bromide (TBAB) and tetrabutylammonium chloride (TBAC) by the transient hot-wire using parylene-coated probe

Kyosuke Fujiura, Yu Nakamoto, Yoshihiro Taguchi, Ryo Ohmura, Yuji Nagasaka

Fluid Phase Equilibria 413 129 - 136 2015.09

Research paper (scientific journal), Joint Work, Accepted

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Surface tension between CO2 Gas and Tetra-n-butylammonium Bromide Aqueous Solution

Hotaka Akiba and Ryo Ohmura

The Journal of Chemical Thermodynamics 92 72 - 75 2015.09

Research paper (scientific journal), Joint Work, Accepted

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Vibrational spectra of deuterated methane and water molecules in structure i clathrate hydrate from ab initio MD simulation

Hiratsuka Masaki, Ohmura Ryo, Sum Amadeu K., Yasuoka Kenji

Molecular Simulation 41 ( 10-12 ) 813 - 817 2015.08

ISSN 0892-7022

The deuteration of the lattice molecules in clathrate hydrates is a widely used experimental technique to clearly separate the vibrational modes. However, the effect of the deuteration on the vibrational spectra and molecular motions is not fully understood. Since the guest-host coupling may change the vibrational spectra, a detailed analysis of the vibrational spectra of deuterated clathrate hydrate is significant in the understanding of the mechanism of the vibrational shift. In this study, the vibrational spectra of the deuterated methane hydrates were calculated by ab initio molecular dynamics simulation. The intramolecular vibrational frequency of the methane in D<inf>2</inf>O lattice and deuterated methane in H<inf>2</inf>O lattice was calculated and compared with the pure methane hydrate. The bending, rocking and overtone of the bending mode was also reported. The effect of coupling of the rattling motions of guest and host molecules on the vibrational spectra was revealed.

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Crystal Growth of Clathrate Hydrates Formed with Methane + Carbon Dioxide Mixed Gas at Gas/liquid Interface and in Liquid Water

Hiroki Ueno, Hotaka Akiba, Satoru Akatsu and Ryo Ohmura

New Journal of Chemistry 39 8254 - 8262 2015.07

Research paper (scientific journal), Joint Work, Accepted

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Phase Behavior and Structural Characterization of Ionic Clathrate Hydrate Formed with Tetra-n-butylphosphonium Hydroxide: Discovery of Primitive Crystal Structure

Takayuki Kobori, Sanehiro Muromachi, Tatsuo Yamasaki, Satoshi Takeya, Yoshitaka Yamamoto, Ryo Ohmura

Crystal Growth & Design 15 3862 - 3867 2015.06

Research paper (scientific journal), Joint Work, Accepted

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Crystal Growth of Ionic Semiclathrate Hydrate Formed at the interface between CO2 Gas and Tetra-n-butylammonium Bromide Aqueous Solution

Hotaka Akiba, Hiroki Ueno, Ryo Ohmura

Crystal Growth & Design 15 3963 - 3968 2015.06

Research paper (scientific journal), Joint Work, Accepted

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A molecular dynamics study of guest-host hydrogen bonding in alcohol clathrate hydrates

Hiratsuka Masaki, Ohmura Ryo, Sum Amadeu K., Alavi Saman, Yasuoka Kenji

Physical Chemistry Chemical Physics 17 ( 19 ) 12639 - 12647 2015.05

ISSN 1463-9076

Clathrate hydrates are typically stabilized by suitably sized hydrophobic guest molecules. However, it has been experimentally reported that isomers of amyl-alcohol C<inf>5</inf>H<inf>11</inf>OH can be enclosed into the 51264 cages in structure II (sII) clathrate hydrates, even though the effective radii of the molecules are larger than the van der Waals radii of the cages. To reveal the mechanism of the anomalous enclathration of hydrophilic molecules, we performed ab initio and classical molecular dynamics simulations (MD) and analyzed the structure and dynamics of a guest-host hydrogen bond for sII 3-methyl-1-butanol and structure H (sH) 2-methyl-2-butanol clathrate hydrates. The simulations clearly showed the formation of guest-host hydrogen bonds and the incorporation of the O-H group of 3-methyl-1-butanol guest molecules into the framework of the sII 51264 cages, with the remaining hydrophobic part of the amyl-alcohol molecule well accommodated into the cages. The calculated vibrational spectra of alcohol O-H bonds showed large frequency shifts due to the strong guest-host hydrogen bonding. The 2-methyl-2-butanol guests form strong hydrogen bonds with the cage water molecules in the sH clathrate, but are not incorporated into the water framework. By comparing the structures of the alcohols in the hydrate phases, the effect of the location of O-H groups in the butyl chain of the guest molecules on the crystalline structure of the clathrate hydrates is indicated.

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Clathrate Hydrate Crystal Growth in Natural Gas Saturated Water Flow

Muhammad Aifaa, Kazuki Imasato, and Ryo Ohmura

Crystal Growth & Design 15 2853 - 2858 2015.04

Research paper (scientific journal), Joint Work, Accepted

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Characterization of the ionic clathrate hydrate of tetra-n-butylammonium acrylate

Sanehiro Muromachi, Masato Kida, Satoshi Takeya, Yoshitaka Yamamoto, Ryo Ohmura

Canadian Journal of Chemistry 93 ( 9 ) 954 - 959 2015.04

Research paper (scientific journal), Joint Work, Accepted

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Molecular dynamics study of guest-host hydrogen bonding in alcohol clathrate hydrates

Masaki Hiratsuka, Ryo Ohmura, Amadeu K Sum, Saman Alavi and Kenji Yasuoka

Physical Chemistry Chemical Physics (Royal Society of Chemistry) 17 12639 - 12647 2015.03

Research paper (scientific journal), Joint Work, Accepted

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Experiments and thermodynamic simulations for continuous separation of CO2 from CH4+CO2 gas mixture utilizing hydrate formation

Shuhei Tomita, Satoru Akatsu, Ryo Ohmura

Applied Energy (Elsevier) 146 104 - 110 2015.03

Research paper (scientific journal), Joint Work, Accepted

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Effect of nitrogen atom substitution in cyclic guests on properties of sH clathrate hydrates

Kazuki Imasato, Kotaro Murayama, Satoshi Takeya, Saman Alavi, Ryo Ohmura

Canadian Journal of Chemistry (National Research Council of Canada) 93 ( 8 ) 906 - 912 2015.03

Research paper (scientific journal), Joint Work, Accepted

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Phase equilibrium for ionic semiclathrate hydrates formed in the system of water + tetra-n-butylammonium bromide pressurized with carbon dioxide

Kobori Takayuki, Muromachi Sanehiro, Ohmura Ryo

Journal of Chemical and Engineering Data 60 ( 2 ) 299 - 303 2015.02

ISSN 0021-9568

This paper reports the vapor-liquid-hydrate three phase equilibrium conditions of ionic semiclathrate hydrates formed in the system of water + tetra-n-butylammonium bromide pressurized with carbon dioxide. The three phase equilibrium temperatures were measured in the ranges from 278.8 to 287.4 K of temperature and from 0.05 to 0.45 of mass fraction of tetra-n-butylammonium bromide (w_TBAB). Measurements were performed at the system pressures of 0.3 MPa, 0.6 MPa, and 1 MPa. For the three system pressures, the equilibrium temperatures increased with the increase in w_TBAB for w_TBAB < 0.35 and decreased for w_TBAB > 0.40. The highest equilibrium temperatures were obtained at w_TBAB = 0.35 and 0.40. The equilibrium temperatures of the tetra-n-butylammonium bromide + carbon dioxide hydrates were higher than those of the simple tetra-n-butylammonium bromide hydrates formed under atmospheric pressure. The improvement of the thermodynamic stability of the tetra-n-butylammonium bromide + carbon dioxide hydrates is ascribed to the incorporation of carbon dioxide molecules into the hydrate cages. The data obtained in the present study may be utilized to specify the thermodynamic conditions to form the tetra-n-butylammonium bromide + carbon dioxide hydrates without forming the simple tetra-n-butylammonium hydrates.

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Experimental measurements of carbon dioxide solubility in aqueous tetra-n-butylammonium bromide solutions

Sanehiro Muromachi, Atsushi Shijima, Hiroyuki Miyamoto, Ryo Ohmura

The Journal of Chemical Thermodynamics (Elsevier) 85 94 - 100 2015.01

Research paper (scientific journal), Joint Work

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Crystal Growth of Clathrate Hydrate in Flowing Liquid Water System Saturated with Methane Gas

Muhammad Aifaa, Takehide Kodama, and Ryo Ohmura

Crystal Growth & Design (American Chemical Society) 15 ( 2 ) 559 - 563 2015.01

Research paper (scientific journal), Joint Work, Accepted

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SURFACTANT EFFECTS ON CRYSTAL GROWTH OF CLATHRATE HYDRATE AT THE INTERFACE OF WATER AND HYDROPHOBIC-GUEST LIQUID

Makoto Mitarai, Masatoshi Kishimoto, Donguk Suh, and Ryo Ohmura

Crystal Growth & Design (American Chemical Society) 15 ( 1 ) 812 - 821 2015.01

Research paper (scientific journal), Joint Work, Accepted

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Crystal growth of clathrate hydrates formed with methane + carbon dioxide mixed gas at the gas/liquid interface and in liquid water

Ueno Hiroki, Akiba Hotaka, Akatsu Satoru, Ohmura Ryo

New Journal of Chemistry 39 ( 11 ) 8254 - 8262 2015

ISSN 1144-0546

Visual observations of CH₄ + CO₂ hydrate crystal growth formed at the gas/liquid interface and in liquid water presaturated with a mixed gas have been made. The compositions of the CH₄ + CO₂ gaseous mixture were 40:60 and 30:70 for the gas/liquid interface observations, 30:70 and 70:30 for water saturated with the guest gas. The feed gas compositions of the CH₄ and CO₂ gaseous mixture were 40:60 and 30:70 for the gas/liquid interface observations, or 30:70 and 70:30 for liquid water. The crystal morphology of the CH₄ + CO₂ hydrate observed in both feed gas compositions was similar. This may be ascribed to the fact that the molar ratios of CO₂ to CH₄ in the liquid phase ranged from 90:10 to 97:3 due to the greater solubility of CO₂ in water. These results suggest that the crystal morphology of the CH₄ + CO₂ hydrate may be controlled by the guest composition in the liquid phase, not by the feed gas composition. As the system subcooling increased, the shape of the hydrate crystals changed from polygons to sword-like or dendrites. The implications for the process design of the hydrate-based technologies are discussed based on the observations.

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Effect of fuel boiling point of pool flame for the flame extinction by CO₂ hydrate

Sugahara Akito, Nakano Hirotaka, Yokomori Takeshi, Ohmura Ryo, Ueda Toshihisa

2015

Experimental investigations to extinguish pool flames by CO₂ hydrate powder and dry ice powder have been done. Methanol and 1-hexanol are used as a fuel of pool flames. The boiling point of the methanol, 67.4 °C, is lower than that of the water, while that of the 1-hexanol, 157 °C, is higher than that of the water. A variation in the flame shape to extinction is recorded by a high-speed video camera. Critical mass for extinction, which is defined as a minimum mass of fire extinguishing agent for extinction, extinction time, temperature variation in and above the fuel are measured. In the case of a methanol pool flame, more critical mass of CO₂ hydrate is necessary compared to the dry ice to supply same mass of CO₂ gas. This indicates that the supply of CO₂ gas plays a key role to extinguish the methanol pool flame, which dilutes the methanol gas and weakens the mixing between methanol gas and air. In the case of 1-hexanol, less critical mass of CO₂ hydrate is necessary compared to the dry ice. In this case, the water in CO₂ hydrate dilutes and cools down the 1-hexanol which results in a decrease in the vaporization of the 1-hexanol.

Crystal Growth Behavior of Methane Hydrate in the Presence of Liquid Hydrocarbon

Kazuki Imasato, Hiroki Tokutomi, and Ryo Ohmura

Crystal Growth & Design (American Chemical Society) 15 ( 1 ) 428 - 433 2014.11

Research paper (scientific journal), Joint Work, Accepted

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Anisotropic Lattice Expansion of Structure H Clathrate Hydrates Induced by Help Guest: Experiments and Molecular Dynamics Simulations

Kotaro Murayama, Satoshi Takeya, Saman Alavi and Ryo Ohmura

Journal of Physical Chemistry Part C (American Chemical Society) 118 21323 - 21330 2014.08

Research paper (scientific journal), Joint Work, Accepted

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Natural supersaturation conditions needed for nucleation air clathrate hydrates in deep ice sheets

Tsutomu Uchida, Keita Yasuda, Yuya Oto, Renkai Shen and Ryo Ohmura

Journal of Glaciology (international glaciological society) 60 1111 - 1116 2014.08

Research paper (scientific journal), Joint Work, Accepted

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Guest-induced symmetry lowering of an ionic clathrate material for carbon capture

S. Muromachi, K. A. Udachin, K. Shin, S. Alavi, I. L. Moudrakovski, R.Ohmura and J. A. Ripmeester

Chemical Communications (Royal Society of Chemistry) 50 11476 - 11479 2014.05

Research paper (scientific journal), Joint Work, Accepted

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Vibrational Spectra of Deuterated Methane and Water Molecules in Structure I Clathrate Hydrate from ab initio MD simulation

Masaki Hiratsuka, Ryo Ohmura1, Amadeu K. Sum and Kenji Yasuoka

Molecular Simulation (Taylor & Francis) Accepted for publicatino 2014.05

Research paper (scientific journal), Joint Work, Accepted

Increasing molecular O3 storage capacity in a clathrate hydrate

Kazutoshi Shishido, Sanehiro Muromachi, Ryo Nakamura, Satoshi Takeyab and Ryo Ohmura

New Journal of Chemistry (Royal Society of Chemistry) 38 3160 - 3165 2014.05

Research paper (scientific journal), Accepted

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Phase equilibrium and crystallographic structure of clathrate hydrate formed in argon + 2,2-dimethylbutane + water system

Kotaro Murayama, Satoshi Takeya, Ryo Ohmura

Fluid Phase Equilibria (Elsevier) 365 ( 1 ) 64-67 2014.04

Research paper (scientific journal), Joint Work, Accepted

Clathrate-hydrate formation from a hydrocarbon gas mixture: compositional evolution of formed hydrate during an isobaric semi-batch hydrate-forming operation

Wataru Kondo, Kaoru Ohtsuka, Ryo Ohmura, Satoshi Takeya, and Yasuhiko H. Mori

Applied Energy (Elsevier) 113 ( 1 ) 864-871 2014.04

Research paper (scientific journal), Joint Work, Accepted

Comparative study of large-scale hydrogen storage technologies: Is hydrate-based storage at advantage over existing technologies?

Makoto Ozaki, Shigeo Tomura, Ryo Ohmura and Yasuhiko H. Mori

International Journal of Hydrogen Energy (Elsevier; International Association for Hydrogen Energy) 39 ( 1 ) 3327-3341 2014.04

Research paper (scientific journal), Joint Work, Accepted

Characterization of clathrate hydrates formed with CH4 or CO2 plus tetrahydropyran

Kento Iino, Satoshi Takeya, Ryo Ohmura

Fuel (Elsevier) 122 ( 2 ) 270-276 2014.02

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibria for Ionic Semiclathrate Hydrate Formed with Tetrabutylphosphonium Chloride plus CO2, CH4, or N2

Kento Iino, Yusuke Sakakibara, Takuya Suginaka Ryo Ohmura

Journal of Chemical Thermodynamics (Elsevier) 71 ( 1 ) 133-136 2014.02

Research paper (scientific journal), Single Work, Accepted

Characterization of Tetra-n-butylphosphonium Bromide Semiclathrate Hydrate by Crystal Structure Analysis

Sanehiro Muromachi, Satoshi Takeya, Yoshitaka Yamamoto, Ryo Ohmura

CrstEngComm (Royal Society of Chemistry) 16 ( 6 ) 2056-2060 2014.02

Research paper (scientific journal), Joint Work, Accepted

Crystal Growth of Clathrate Hydrate in Liquid Water in Contact with Methane + Ethane + Propane Gas Mixture

Takehide Kodama, Ryo Ohmura

Journal of Chemical Technology and Biotechnology (Wiley; Society of Chemical Industry) 89 1982 - 1986 2014.01

Research paper (scientific journal), Joint Work, Accepted

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Preservation of carbon dioxide clathrate hydrate coexisting with sucrose under domestic freezer conditions

Tadaaki Sato, Satoshi Takeya, Hironori D. Nagashima, Ryo Ohmura

Journal of Food Engineering (Elsevier) 120 ( 1 ) 69-74 2014.01

Research paper (scientific journal), Joint Work, Accepted

Thermodynamic simulations of hydrate-based removal of carbon dioxide and hydrogen sulfide from low-quality natural gas

Satoru Akatsu, Shuhei Tomita, Yasuhiko H. Mori, Ryo Ohmura

Industrial & Engineering Chemistry Research (American Chemical Society) 52 ( 47 ) 15165-15176 2013.12

Research paper (scientific journal), Joint Work, Accepted

Phase equilibrium condition measurements in nitrogen and air clathrate hydrate forming systems at temperatures below freezing point of water

Keita Yasuda, Yuya Oto, Renkai Shen, Tsutomu Uchida, Ryo Ohmura

Journal of Chemical Thermodynamics (Elsevier) 67 143-147 2013.12

Research paper (scientific journal), Joint Work, Accepted

Thermodynamic Modeling for Clathrate Hydrates of Ozone

Sanehiro Muromachi, Hironori D. Nagashima, Jean-Michel Herri, Ryo Ohmura

Journal of Chemical Thermodynamics (Elsevier) 64 ( 1 ) 193-197 2013.06

Research paper (scientific journal), Joint Work, Accepted

パリレン絶縁プローブ非定常細線法によるTBABハイドレートの熱伝導率測定

永冨達也，田口良広，大村　亮，長坂　雄次

日本機械学会論文集 B編 79 ( 6 ) 1155-1163 2013.06

Research paper (scientific journal), Joint Work, Accepted

Effect of Guest Size and Conformation on Crystal Structure and Stability of Structure H Clathrate Hydrates: Experimental and Molecular Dynamics Simulation Studies

Kyouichi Tezuka, Kotaro Murayama, Satoshi Takeya, Alavi Saman, Ryo Ohmura

Journal of Physical Chemistry Part C (Americal Chemical Society) 117 ( 20 ) 10473-10482 2013.05

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium for Ionic Semiclathrate Hydrate Formed with CO2, CH4, or N2 plus Tetrabutylphosphonium Bromide

Takuya Suginaka, Hiroki Sakamoto, Kento Iino, Yusuke Sakakibara, Ryo Ohmura

Fluid Phase Equilibria (Elsevier) 344 108-111 2013.04

Research paper (scientific journal), Joint Work, Accepted

Crystal growth of ionic semiclathrate hydrate formed in CO2 gas + tetrabutylammonium bromide aqueous solution system

Shunsuke Koyanagi, Ryo Ohmura

Crystal Growth & Design (American Chemical Society) 13 ( 5 ) 2087-2093 2013.03

Research paper (scientific journal), Joint Work, Accepted

Water Proton Configurations in Structures I, II, and H Clathrate Hydrate Unit Cells

Fumihito Takeuchi, Masaki Hiratsuka, Ryo Ohmura, Saman Alavi, Amadeu K. Sum, Kenji Yasuoka

Journal of Chemical Physics (American Institute of Physics) 138 ( 12 ) 124504 2013.03

Research paper (scientific journal), Joint Work, Accepted

Synthesis and characterization of structure H hydrate formed with carbon dioxide and 3,3-dimethyl-2-butanone

Kyoichi Tezuka, Renkai Shen, Taku Watanabe, Satoshi Takeya, Saman Alavi, John A. Ripmeester, Ryo Ohmura

Chemical Communications (Royal Society of Chemistry) 49 505-507 2013.01

Research paper (scientific journal), Joint Work, Accepted

Experimental investigation of flame spreading over pure methane hydrate in a laminar boundary layer

Yoshihiro Maruyama, Masaru Joe Fuse, Takeshi Yokomori, Ryo Ohmura, Shigeru Watanabe, Toru Iwasaki, Wataru Iwabuchi and Toshihisa Ueda

Proceedings of the Combustion Institute (Elsevier/Combustion Institute) 34 2131-2138 2013.01

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium of Ionic Semiclathrate Hydrates formed with Tetrabutylammonium Bromide and Tetrabutylammonium Chloride

Kai Sato, Hiroki Tokutomi, Ryo Ohmura

Fluid Phase Equilibria (Elsevier) 337 115-118 2013.01

Research paper (scientific journal), Joint Work, Accepted

Diffraction Enhanced X-ray Imaging under Low-Temperature Conditions – Non-destructive observations of Clathrate Gas Hydrates –

Satoshi Takeya, Kazumasa Honda, Yoshito Gotoh, Akio Yoneyama, Kazuhiro Ueda, Atsushi Miyamoto, Takeo Hondoh, Akira Hori, Duo Sun, Ryo Ohmura, Kazuyuki Hyodo and Tohoru Takeda

Journal of Synchrotron Radiation (International Union of Crystallography) 19 ( 6 ) 1038-1042 2012.12

Research paper (scientific journal), Joint Work, Accepted

Vibrational Modes of Methane in the Structure H Clathrate Hydrate from Ab initio Molecular Dynamics Simulation

Masaki Hiratsuka, Ryo Ohmura, Amadeu K. Sum, Kenji Yasuoka

The Journal of Chemical Physics (American Institute of Physics) 137 ( 14 ) 144306 2012.11

Research paper (scientific journal), Joint Work, Accepted

Molecular Storage of Ozone in a Clathrate Hydrate: An Attempt at Preserving Ozone at High Concentrations

Takahiro Nakajima, Taisuke Kudo, Ryo Ohmura, Satoshi Takeya, Yasuhiko H. Mori

PLOS ONE (Public Library of Science) 7 ( 11 ) e48563 2012.11

Research paper (scientific journal), Joint Work, Accepted

Dynamic Behavior of Clathrate Hydrate Growth in Gas/Liquid/Liquid System

Ishida, Yosuke; Takahashi, Yusuke; Ohmura, Ryo

Crystal Growth & Design (America Chemical Society) 12 ( 6 ) 3271-3277 2012.05

Research paper (scientific journal), Joint Work, Accepted

Hydrate Phase Equilibrium in the System of Carbon Dioxide + 2,2-Dimethylbutane + Water at Temperatures below Freezing Point of Water

Renkai Shen; Kyoichi Tezuka; Tsutomu Uchida; Ryo Ohmura

Journal of Chemical Thermodynamics (Elsevier) 53 27-29 2012.05

Research paper (scientific journal), Joint Work

Crystal Growth of Clathrate Hydrate at the Interface between Seawater and Hydrophobic-guest Liquid: Effect of Elevated Salt Concentration

Masatoshi Kishimoto, Satoshi Iijima and Ryo Ohmura

Industrial and Engineering Chemistry Research (American Chemical Society) 51 ( 14 ) 5224–5229 2012.04

Research paper (scientific journal), Joint Work, Accepted

Phase equilibrium for ozone-containing hydrates formed from an ozone + oxygen gas mixture coexisting with gaseous carbon dioxide and liquid water

Sanehiro Muromachi, Ryo Ohmura and Yasuhiko H. Mori

Journal of Chemical Thermodynamics (Elsevier) 49 1-6 2012.04

Research paper (scientific journal), Joint Work, Accepted

Engineering investigation of hydrogen storage in the form of a clathrate hydrate: conceptual designs of underground hydrate storage silos

Toshio Shibata, Hiroshi Yamachi, Ryo Ohmura and Yasuhiko H. Mori

International Journal of Hydrogen Energy (Elsevier) 37 7612-7623 2012.04

Research paper (scientific journal), Joint Work, Accepted

Using Submarine Heat Pumps for Efficient Gas Production

Yasuhiko Mori, Jun-ichi Ochiai and Ryo Ohmura

Energies (MDPI Publishing) 5 ( 3 ) 599-604 2012.03

Research paper (scientific journal), Joint Work, Accepted

Thermodynamic Properties of Ionic Semiclathrate Hydrate Formed with Tetrabutylphosphonium Bromide

Suginaka, T.; Sakamoto, H.; Iino, K.; Takeya, S.; Nakajima, M.; Ohmura, R.

Fluid Phase Equilibria (Elsevier) 317 25-28 2012.03

Research paper (scientific journal), Joint Work, Accepted

Thermodynamic Stability of Structure H Hydrates Based on the Molecular Properties of Large Guest Molecules

Kyoichi Tezuka, Tatsuhiko Taguchi, Saman Alavi, Amadeu K. Sum and Ryo Ohmura

Energies (MDPI Publishing) 5 ( 2 ) 459-465 2012.02

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium for Clathrate Hydrates Formed with fluoromethane + Propan-2-ol, 2-Methyl-2-propanol, or 2-Propanone

Imai, M.; Oto, Y.; Nitta, S.; Takeya, S.; Ohmura, R.

The Journal of Chemical Thermodynamics (Elsevier) 47 17 – 20 2012.02

Research paper (scientific journal), Joint Work, Accepted

Molecular Vibrations of Methane Molecules in the Structure I Clathrate Hydrate from Ab Initio Molecular Dynamics Simulation

Hiratsuka, M.; Ohmura, R.; Sum, A. K.; Yasuoka, K.

Journal of Chemical Physics (American Institute of Physics) 136 Article No. 044508 2012.02

Research paper (scientific journal), Joint Work, Accepted

Correlation of growth rate of hydrate layer at guest/liquid-water interface to mass transfer resistance

Masatoshi Kishimoto and Ryo Ohmura

Energies (MDPI Publishing (Basel, Switzerland)) 5 ( 1 ) 92-100 2012.01

Research paper (scientific journal), Joint Work, Accepted

Preservation of Carbon Dioxide Clathrate Hydrate at Temperatures below Water Freezing Point under Atmospheric Pressure

Sun, D.; Shimono, Y.; Takeya, S.; Ohmura, R.

Industrial & Engineering Chemistry Research (American Chemical Society) 50 ( 24 ) 13854-13858 2011.10

Research paper (scientific journal), Joint Work, Accepted

Molecular Storage of Ozone in a Clathrate Hydrate Formed from an O3 + O2 + CO2 Gas Mixture

Nakajima, T.; Akatsu, S.; Ohmura, R.; Takeya, S.; Mori, Y. H.

Angewandte Chemie International Edition (Wiley / Gesellschaft Deutscher Chemiker) 50 ( 44 ) 10340-10343 2011.10

Research paper (scientific journal), Joint Work, Accepted

Synthesis, characterization and thermal-property measurements of ionic semiclathrate hydrates formed with tetrabutylphosphonium chloride and tetrabutylammonium acrylate

Sakamoto, H.; Sato, K.; Shiraiwa, K.; Takeya, S.; Nakajima, M.; Ohmura, R.

RSC Advances (Royal Society of Chemistry) 1 ( 2 ) 315-322 2011.08

Research paper (scientific journal), Joint Work, Accepted

Crystal growth of clathrate hydrate in gas/liquid/liquid system: Variations in crystal growth behavior

Ishida, Y., Sakemoto, R.; Ohmura, R.

Chemistry – A European Journal (Wiley/Gesellschaft Deutscher Chemiker) 17 ( 34 ) 9471-9477 2011.07

Research paper (scientific journal), Joint Work, Accepted

Crystal Growth of Clathrate Hydrate in Liquid Water Saturated with a Simulated Natural Gas

Watanabe, S.; Saito, K.; Ohmura, R.

Crystal Growth & Design (American Chemical Society) 11 ( 7 ) 3235-3242 2011.07

Research paper (scientific journal), Joint Work, Accepted

Phase equilibrium for clathrate hydrates formed from an ozone + oxygen gas mixture coexisting with carbon tetrachloride or 1,1-dichloro-1-fluoroethane

Muromachi, S.; Nakajima, T.; Ohmura, R.; Mori, Y. H.

Fluid Phase Equilibria (Elsevier) 305 145-151 2011.06

Research paper (scientific journal), Joint Work, Accepted

Thermodynamic Properties of Methane/Water Interface Predicted by Molecular Dynamics Simulations

Sakamaki, R.; Sum, A. K.; Narumi, T.; Ohmura, R.; Yasuoka, K.

Journal of Chemical Physics (American Institute of Physics) 134 ( 14 ) 144702 2011.04

Research paper (scientific journal), Joint Work, Accepted

13C NMR Studies of Hydrocarbon Guests in Synthetic Structure H Gas Hydrates: Experiment and Computation

Lee, J. W., Lu, H., Moudrakovski, I. L.; Ratcliffe, C. I.; Ohmura, R.; Alavi, S.; Ripmeester, J. A.

Journal of Physical Chemistry A (American Chemical Society) 115 ( 9 ) 1650-1657 2011.03

Research paper (scientific journal), Joint Work, Accepted

A Molecular Dynamics Study Ethanol-Water Hydrogen Bonding in Binary Structure I Hydrate with CO2

Alavi, S.; Ohmura, R.; Ripmeester, J. A.

Journal of Chemical Physics (American Institute of Physics) 134 ( 5 ) Paper No. 054702 2011.02

Research paper (scientific journal), Joint Work, Accepted

Crystal Growth of Clathrate Hydrate at the Interface between Hydrocarbon-gas Mixture and Liquid Water

Saito, K.; Kishimoto, M.; Tanaka, R.; Ohmura, R.

Crystal Growth & Design (American Chemical Society) 11 ( 1 ) 295-301 2011.01

Research paper (scientific journal), Joint Work, Accepted

Clathrate-hydrate formation from a hydrocarbon gas mixture: evolution of gas-phase composition in a hydrate-forming reactor

Kondo, W.; Ogawa, H.; Ohmura, R.; Mori, Y. H.

Energy & Fuels (American Chemical Society) 24 ( 12 ) 6375-6383 2010.12

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium for Structure H Hydrates Formed with Methane plus Cycloheptane, Cycloheptanone, or Oxacycloheptane

Kozaki, T., Taguchi, T., Takeya, S., Ohmura, R.

Journal of Chemical and Engineering Data (American Chemical Society) 55 ( 9 ) 3059-3062 2010.09

Research paper (scientific journal), Joint Work, Accepted

Guest-host hydrogen bonding and semiclathrate formation in binary ethanol, 1-propanol, and 2-propanol + methane structure II clathrate hydrates

Alavi, S., Takeya, S., Ohmura, R., Woo, T., Ripmeester, J. A.

Journal of Chemical Physics (American Institute of Physics) 133 ( 7 ) 074505/1-8 2010.08

Research paper (scientific journal), Joint Work, Accepted

Synthesis and characterization of clathrate hydrates containing carbon dioxide and ethanol

Makiya, T., Murakami, T., Takeya, S., Sum, A. K., Alavi, S., Ohmura, R.

Physical Chemistry Chemical Physics (Royal Society of Chemistry) 12 ( 33 ) 9927-9932 2010.08

Research paper (scientific journal), Joint Work, Accepted

Clathrate Hydrates for Ozone Preservation

Muromachi, S., Ohmura, R., Takeya, S., Mori, Y. H.

Journal of Physical Chemistry B (American Chemical Society) 114 ( 35 ) 11430-11435 2010.08

Research paper (scientific journal), Joint Work, Accepted

Correlation of hydrate-film growth rate at the guest-liquid/water interface to mass transfer resistance

Saito, K., Sum, A. K., Ohmura, R.

Industrial & Engineering Chemistry Research (American Chemical Society) 49 ( 15 ) 7102-7103 2010.07

Research paper (scientific journal), Joint Work, Accepted

Engineering investigation of hydrogen storage in the form of clathrate hydrates: Conceptual design of hydrate production plants

Nakayama, T., Tomura, S., Ozaki, M., Ohmura, R., Mori, Y. H.

Energy & Fuels (American Chemical Society) 24 ( 4 ) 2576-2588 2010.04

Research paper (scientific journal), Joint Work

Clathrate hydrate crystal growth at the seawater/hydrophobic-guest-liquid interface

Sakemoto, R., Sakamoto, H., Shiraiwa, K., Ohmura, R., Uchida, T.

Crystal Growth & Design (American Chemical Society) 10 ( 3 ) 1296-1300 2010.03

Research paper (scientific journal), Joint Work, Accepted

Phase equilibrium for clathrate hydrates formed with methane + ethane + propane mixtures at temperatures below the freezing point of water

Yasuda, K., Ogawa, H. Ohmura, R.

Journal of Chemical & Engineering Data (American Chemical Society) 55 ( 1 ) 358-361 2010.01

Research paper (scientific journal), Joint Work, Accepted

Raman peak frequencies of fluoromethane molecules measured in the clathrate hydrate crystals: Experimental investigations and density functional theory calculations

Uchida, T., Ohmura, R., Hori, A.

Journal of Physical Chemistry A (American Chemical Society) 114 ( 1 ) 317-323 2010.01

Research paper (scientific journal), Joint Work, Accepted

Statistical-thermodynamics modeling of clathrate hydrate forming systems suitable as working media of a hydrate-based refrigeration system

Takeuchi, F., Ohmura, R., Yasuoka, K.

International Journal of Thermophysics (Springer) 30 ( 6 ) 1838-1852 2009.12

Research paper (scientific journal), Joint Work, Accepted

Binary ethanol-methane clathrate hydrate formation in the system CH4-C2H5OH-H2O: confirmation of structure II hydrate formation

Yasuda, K., Takeya, S., Sakashita, M., Yamawaki, H., Ohmura, R.

Journal of Physical Chemistry C (American Chemical Society) 113 12598-12601 2009.06

Research paper (scientific journal), Joint Work, Accepted

Crystal growth of clathrate hydrates formed at the interface of liquid water and gaseous methane, ethane or propane: variations in crystal morphology

Tanaka, R., Sakemoto, R., Ohmura, R.

Crystal Growth & Design (American Chemical Society) 9 ( 5 ) 2529-2536 2009.05

Research paper (scientific journal), Joint Work, Accepted

Fire extinction using carbon dioxide hydrate

Hatakeyama, T., Aida, E., Yokomori, T., Ohmura, R., Ueda, T.

Industrial & Engineering Chemistry Research (American Chemical Society) 48 ( 8 ) 4083-4087 2009.04

Research paper (scientific journal), Joint Work, Accepted

Combustion characteristics of methane hydrate in a laminar boundary layer

Nakamura, Y., Katsuki, R., Yokomori, T., Ohmura, R., Takahashi, M., Iwasaki, T., Uchida, K., Ueda, T.

Energy and Fuels (American Chemical Society) 23 ( 2 ) 1445-1449 2009.02

Research paper (scientific journal), Joint Work, Accepted

Thermodynamic Simulations of Isobaric Hydrate-Forming Operations for Natural Gas Storage

Ogawa, H., Imura, N., Miyoshi, T., Ohmura, R., Mori, Y. H.

Energy and Fuels (American Chemical Society) 23 ( 2 ) 849-856 2009.02

Research paper (scientific journal), Joint Work, Accepted

Characterization of the Clathrate hydrate formed with methane and propan-1-ol

Yasuda, K., Takeya, S., Sakashita, M., Yamawaki, H., Ohmura, R.

Industrial and Engineering Chemistry Research (American Chemica Society) 48 ( 20 ) 9335-9337 2009

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium and Crystallographic Structures of Clathrate Hydrates Formed in Methane + 2,2-Dimethylpentane + Water System

Kozaki, T., Takeya, S., Ohmura, R.

Journal of Chemical and Engineering Data (American Chemical Society) 53 ( 12 ) 2820-2823 2008.12

Research paper (scientific journal), Joint Work, Accepted

Clathrate hydrate formation from cyclopentane-in-water emulsions

Industrial and Engineering Chemistry Research (American Chemical Society) 掲載決定 2008.09

Research paper (scientific journal), Joint Work, Accepted

Visual observation of dissociation of methane hydrate crystals in a glass micro model: Production and transfer of methane

Daisuke Katsuki, Ryo Ohmura, Takao Ebinuma and Hideo Narita

Journal of Applied Physics (American Institute of Physics) 掲載決定 2008.09

Research paper (scientific journal), Joint Work, Accepted

Critical size for guest molecules to occupy dodecahedral cage of clathrate hydrates

T. Uchida, R. Ohmura and A. Hori

Journal of Physical Chemistry C (American Chemical Society) 112 ( 12 ) 4719-4724 2008.03

Research paper (scientific journal), Joint Work, Accepted

Phase equilibrium for clathrate hydrates formed with methane, ethane, propane or carbon dioxide at temperatures below the freezing point of water

K. Yasuda and R. Ohmura

Journal of Chemical and Engineering Data (American Chemical Society) 7月16日掲載決定 2008

Research paper (scientific journal), Joint Work, Accepted

Phase equilibrium for structure II hydrates formed with methylfluoride coexisting with cyclopentane, fluorocyclopentane, cyclopentene, or tetrahydropyran

S. Takeya, K. Yasuda and R. Ohmura

Journal of Chemical and Engineering Data (American Chemical Society) 53 ( 2 ) 531-534 2007.12

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium Calculation for Clathrate Hydrates Based on a Statistical Thermodynamics Model: An Attempt to Optimize the Kihara Parameters for Methane and Ethane

E. Sato, T. Miyoshi, R. Ohmura, K. Yasuoka

Japanese Journal of Applied Physics (The Japan Society of Applied Physics) 46 ( 9A ) 5944-5950 2007.09

Research paper (scientific journal), Joint Work, Accepted

Spectroscopic measurements on binary, ternary and quaternary mixed-gas molecules in clathrate structures

Uchida, T., Takeya, S., Kamata, Y., Ohmura, R., Narita, H.

Industrial and Engineering Chemistry Research (American Chemical Society) 46 ( 14 ) 5080-5087 2007.07

Research paper (scientific journal), Joint Work, Accepted

Thermodynamic stability of type-I and type-II clathrate hydrates depending on the chemical species of the guest substances

Miyoshi, T., Imai, M., Ohmura, R., Yasuoka, K.

Journal of Chemical Physics (American Institute of Physics) 126 234506 2007.07

Research paper (scientific journal), Joint Work, Accepted

Phase equilibrium for clathrate hydrates formed with difluoromethane or krypton, each coexisting with propan-2-ol, 2-methly-2-propanol or 2-propanone

Imai, S., Miyake, K., Ohmura, R., Mori, Y. H.

Journal of Chemical and Engineering Data (American Chemical Society) 52 ( 3 ) 1056-1059 2007.05

Research paper (scientific journal), Joint Work, Accepted

Clathrate hydrate formation by water spraying in a methane + ethane + propane gas mixture: search for the rate-controlling mechanism of hydrate formation in the presence of methylcyclohexane

Kobayashi, T., Imura, N., Ohmura, R., Mori, Y. H.

Energy & Fuels (American Chemical Society) 21 ( 2 ) 545-553 2007.03

Research paper (scientific journal), Joint Work, Accepted

Methane hydrate crystal growth in a porous medium filled with methane-saturated liquid water

D. Katsuki, R. Ohmura, T. Ebinuma & H. Narita

Philosophical Magazine (Taylor & Francis) 87 ( 7 ) 1057-1069 2007.03

Research paper (scientific journal), Joint Work, Accepted

Predicting thermodynamic stability of clathrate hydrates based on molecular-dynamics simulations and its confirmation by phase-equilibrium measurements

Miyoshi, T., Ohmura, R., Yasuoka, K.

Journal of Physical Chemistry C (American Chemical Society) 111 ( 9 ) 3799-3802 2007.03

Research paper (scientific journal), Joint Work, Accepted

Phase equilibrium for structure-I and structure-H hydrates formed with methylfluoride and methylcyclohexane

Takeya, S., Ohmura, R.

Journal of Chemical and Engineering Data (American Chemical Society) 52 ( 2 ) 635-638 2007.03

Research paper (scientific journal), Joint Work, Accepted

“Molecular dynamics simulations of structure-H hydrates formed with methane and 3,3-dimethylpentane or 2,2-dimethylpentane

Miyoshi, T., Ohmura, R., Yasuoka, K.

Molecular Simulation (Taylor and Francis) 33 ( 1-2 ) 65-69 2007.01

Research paper (scientific journal), Single Work, Accepted

Effects of Additives on Formation of CO2 Hydrate Films

T. Uchida, I. Y. Ikeda, R. Ohmura, S. Tsuda

Physics and Chemistry of Ice (Royal Society of Chemistry) 609-618 2007

Research paper (scientific journal), Joint Work, Accepted

Phase equilibrium for clathrate hydrates formed with difluoromethane or krypton each coexisting with fluorocyclopentane

Imai, S., Miyake, K., Ohmura, R. & Mori, Y. H.

Journal of Chemical and Engineering Data (American Chemical Society) 51 ( 6 ) 2222-2224 2006.11

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium for Structure II Hydrates Formed with Krypton Coexisting with Cyclopentane, Cyclopentene or Tetrahydropyran

S. Takeya & R. Ohmura

Journal of Chemical and Engineering Data (American Chemical Society) 51 ( 5 ) 1880-1883 2006.09

Research paper (scientific journal), Joint Work, Accepted

Crystal Lattice Size and Stability of Type H Clathrate Hydrates with Various Large-Molecule Guest Substances

Takeya Satoshi, Akira Hori, Tsutomu Uchida, Ohmura Ryo

Journal of Physical Chemistry B (American Chemical Society) 110 ( 26 ) 12943-12947 2006.07

Research paper (scientific journal), Joint Work, Accepted

Formation, growth and ageing of clathrate hydrate crystals in a porous medium

Katsuki, D., Ohmura, R., Ebinuma, T., Narita, H.

Philosophical Magazine (Taylor and Francis) 86 ( 12 ) 1753-1761 2006.05

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium for Structure-H Hydrate Formed with Krypton and 2,2-Dimethylbutane

Ohmura, R., Takeya, S., Maekawa, T., Uchida, T.

Journal of Chemical & Engineering Data (American Chemical Society) 51 ( 1 ) 161-163 2006.01

Research paper (scientific journal), Joint Work, Accepted

Development of a Novel Hydrate-Based Refrigeration System: a Preliminary Overview

35. Ogawa, T., Itoh, T., Watanabe, K., Tahara, K., Hiraoka, R., Ochiai, J., Ohmura, Ryo, Mori, Y. H.

Applied Thermal Engineering (Elsevier) 26 ( 17-18 ) 2157-2167 2006

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium Measurements and Crystallographic Analyses on Structure-H Type Gas Hydrate Formed from the CH4-CO2-Neohexane-Water System

Uchida, T., Ohmura, R., Ikeda, I. Y., Nagao, J., Takeya, S., Hori, A.

Journal of Physical Chemistry B (American Chemical Society) 110 ( 10 ) 4583-4588. 2006

Research paper (scientific journal), Joint Work, Accepted

Clathrate Hydrate Crystal Growth in Liquid Water Saturated with a Guest Substance: Observations in Methane + Water System

Ohmura, R., Matsuda, S., Uchida, T., Ebinuma, T., Narita, H.

Crystal Growth & Design (American Chemical Society) 5 ( 3 ) 953-957 2005.05

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium for Structure-H Hydrates at Temperatures below the Freezing Point of Water

Ohmura, R., Matsuda, S., Uchida, T., Ebinuma, T., Narita, H.

Journal of Chemical & Engineering Data (American Chemical Society) 50 993-996 2005

Research paper (scientific journal), Joint Work, Accepted

Particle size effect of CH4 hydrate for self-preservation

Takeya, S., Uchida, T., Nagao, J., Ohmura, R., Shimada, W., Kamata, Y., Ebinuma, T., and Narita, H.

Chemical Engineering Science (Elsevier) 60 1383-1387 2005

Research paper (scientific journal), Joint Work, Accepted

Kinetics and Stability of CH4-CO2 Mixed Gas Hydrates during Formation and Long-Term Storage

Uchida, T., Ikeda, I. Y., Takeya, S., Kamata, Y., Ohmura, R., Nagao, J., Zatsepina, O. Y., Buffett, B. A.

ChemPhysChem (Wiley (co-owned by nine European Chemical Societies)) 6 646-654 2005

Research paper (scientific journal), Joint Work, Accepted

Hydrate Formation by Water Spraying in a Methane + Ethane + Propane Gas Mixture: an Attempt at Promoting Hydrate Formation Utilizing Large-Molecule Guest Substances for Structure-H Hydrates

Tsuji, H., Kobayashi, T., Ohmura, R., Mori, Y. H.

Energy & Fuels (American Chemical Society) 19 869-876 2005

Research paper (scientific journal), Joint Work, Accepted

Thermodynamic Simulations of Isobaric Hydrate-forming Operations: Formulation of Computational Scheme and Its Application to Hydrate Formation from a Methane + Ethane + Propane Mixture

Tsuji, H., Kobayashi, T., Okano, Y., Ohmura, R., Yasuoka, K., Mori, Y. H.

Energy & Fuels (American Chemical Society) 19 1587-1597 2005

Research paper (scientific journal), Joint Work, Accepted

Formation and Growth of Structure-H Hydrate Crystals on a Water Droplet in Contact with Methane Gas and Large-Molecule Guest-Substance Liquid

Ohmura, R., Matsuda, S., Itoh, S., Ebinuma, T., Narita, H.

Crystal Growth & Design (American Chemical Society) 5 1821-1824 2005

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium for Clathrate Hydrates Formed with Difluoromethane + either Cyclopentane or Tetra-n-butylammonium Bromide

Imai, S., Okutani, K., Ohmura, R., Mori, Y. H.

Journal of Chemical & Engineering Data (American Chemical Society) 50 1783-1786 2005

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium for Structure-H Hydrates Formed with Methane and Methyl-Substituted Cyclic Ether

Ohmura, R., Matsuda, S., Takeya, S., Ebinuma, T., Narita, H.

International Journal of Thermophysics (Springer) 26 1515-1523 2005

Research paper (scientific journal), Joint Work, Accepted

Decomposition of methane hydrates in sand, sandstone, clays, and glass beads

Uchida, T., Takeya, S., Chuvirin, E. M., Ohmura, R., Nagao, J., Yakushev, V. S., Istomin, V. A., Minagawa, H., Ebinuma, T. and Narita, H.

Journal of Geophysical Research - Solid Earth (American Geophysical Union) 109 B05206 (doi:10.1029/2003JB002771) 2004.05

Research paper (scientific journal), Joint Work, Accepted

Clathrate-hydrate crystal growth in liquid water saturated with a hydrate-forming substance: variations in crystal morphology

Ohmura, R., Shimada, W., Uchida, T., Mori, Y. H., Takeya S., Nagao, J., Minagawa, H., Ebinuma, T. and Narita, H.

Philosophical Magazine (Taylor and Francis) 84 1-16 2004.01

Research paper (scientific journal), Joint Work, Accepted

Two-step formation process of methane-propane mixed gas hydrates in a batch-type reactor

Uchida, T., Moriwaki, M., Takeya, S., Ikeda, Y. I., Ohmura, R., Nagao, J., Minagawa, H., Ebinuma, T., Narita, H., Gohara, K., and Mae, S.

AIChE Journal (AIChE) 50 518-523 2004

Research paper (scientific journal), Joint Work, Accepted

Forming Structure-H Hydrates Using Water Spraying in Methane Gas: Effects of Chemical Species of Large-Molecule Guest Substances

Tsuji, H., Ohmura, R. and Mori, Y. H.

Energy & Fuels (American Chemical Society) 18 418-424 2004

Research paper (scientific journal), Joint Work, Accepted

Clathrate hydrate formation in the system methane + 3-methyl-1-butanol + water: Equilibrium data and crystallographic structures of hydrates

Ohmura, R., Takeya, S. Uchida, T., Ikeda, I. Y., Ebinuma, T. and Narita, H.

Fluid Phase Equilibria (Elsevier) 221 151-156 2004

Research paper (scientific journal), Joint Work, Accepted

Clathrate hydrate formed with methane and 2-propanol: Confirmation of structure-II hydrate formation

Ohmura, R., Takeya, S. Uchida, T., Ebinuma, T.

Industrial & Engineering Chemistry Research (American Chemical Society) 43 4964-4966 2004

Research paper (scientific journal), Joint Work, Accepted

Gas Absorption into “String-of-Beads” Liquid Flow with Chemical Reaction: Application to Carbon-Dioxide Separation

Uchiyama, K., Migita, H., Ohmura, R. and Mori, Y. H.

International Journal of Heat & Mass Transfer (Elsevier) 46 457-468 2003

Research paper (scientific journal), Joint Work, Accepted

Effects of Kinetic Inhibitors on the Formation and Growth of Hydrate Crystals at a Liquid-Liquid Interface

Sakaguchi, H., Ohmura, R. and Mori, Y. H.

Journal of Crystal Growth (Elsevier) 247 631-641 2003

Research paper (scientific journal), Joint Work, Accepted

Statistical Study of Clathrate-Hydrate Nucleation in a Water/Hydrochlorofluorocarbon System: Search for the Nature of the "Memory Effect"

Ohmura, R., Ogawa, M., Yasuoka, K. and Mori, Y. H.

Journal of Physical Chemistry B (American Chemical Society) 107 5289-5293 2003

Research paper (scientific journal), Joint Work, Accepted

Viscosity of Aqueous CO2 Solutions Measured by Dynamic Light Scattering

Uchida, T., Ohmura, R., Nagao, J., Takeya, S., Ebinuma, T. and Narita, H.

Journal of Chemical & Engineering Data (American Chemical Society) 48 1225-1229 2003

Research paper (scientific journal), Joint Work, Accepted

Phase Equilibrium for Structure-H Hydrates Formed with Methane and each of Pinacolone (3,3-dimethyl-2-butanone) and Pinacolyl alcohol (3,3-dimethyl-2-butanol)”

Ohmura, R., Uchida, T., Takeya S., Nagao, J., Minagawa, H., Ebinuma, T. and Narita, H.

Journal of Chemical & Engineering Data (American Chemical Society) 48 1337-1340 2003

Research paper (scientific journal), Joint Work, Accepted

Clathrate Hydrate Formation in (Methane + Water + Methylcyclohexanone) Systems: the First Phase Equilibrium Data

Ohmura, R., Uchida, T., Takeya S., Nagao, J., Minagawa, H., Ebinuma, T. and Narita, H.

Journal of Chemical Thermodynamics (Elsevier) 35 2045-2055 2003

Research paper (scientific journal), Joint Work, Accepted

Bending Tests on Clathrate Hydrate Single Crystals

Ohmura, R., Shigetomi, T. and Mori, Y. H.

Philosophical Magazine A (Taylor and Francis) 82 1725-1740 2002

Research paper (scientific journal), Joint Work, Accepted

Structure-I and Structure-H Hydrate Formation Using Water Spraying

Ohmura, R., Kashiwazaki, S., Shiota, S., Tsuji, H. and Mori, Y. H.

Energy & Fuels (American Chemical Society) 16 1141-1147 2002

Research paper (scientific journal), Joint Work, Accepted

Hydrate Formation Using Water Spraying in a Hydrophobic Gas: a Preliminary Study

Fukumoto, K., Tobe, J., Ohmura, R. and Mori, Y. H.

AIChE Journal (AIChE) 47 1899-1904 2001

Research paper (scientific journal), Joint Work, Accepted

Mechanical Properties of Water/Hydrate-Former Phase Boundaries and Phase-Separating Hydrate Films

Ohmura, R., Shigetomi, T. and Mori, Y. H.

Annals of New York Academy of Sciences (New York Academy of Sciences) 912 958-966 2000

Research paper (scientific journal), Joint Work, Accepted

Measurements of Clathrate-Hydrate Film Thickness Using Laser Interferometry

Ohmura, R., Kashiwazaki, S. and Mori, Y. H.

Journal of Crystal Growth (Elsevier) 218 372-380 2000

Research paper (scientific journal), Joint Work, Accepted

クラスレート水和物の物理化学 - エネルギー・環境関連技術のための概論と研究動向レビュー

大村亮，森康彦

Thermal Science and Engineering Vol.7 ( No.2 ) 1999.03

Research paper (scientific journal), Joint Work, Accepted

Formation, Growth and Dissociation of Clathrate Hydrate Crystals in Liquid Water in Contact with a Hydrophobic Hydrate-Forming Liquid

Ohmura, R., Shigetomi, T. and Mori, Y. H.

Journal of Crystal Growth (Elsevier) 196 164-173 1999

Research paper (scientific journal), Single Work, Accepted

Comments on "Solubility of Liquid CO2 in Synthetic Sea Water at Temperatures from 278 K to 293 K and Pressures from 6.44 MPa to 29.49 MPa, and Densities of the Corresponding Aqueous Solutions" (Teng, H.; Yamasaki, A. J. Chem. Eng. Data 1998, 43, 2-5)

Ohmura, R. and Mori, Y. H.,

Journal of Chemical & Engineering Data (American Chemical Society) 44 1432-1433 1999

Research paper (scientific journal), Joint Work, Accepted

Pull-out Test of Clathrate-Hydrate Films at Water/Hydrochlorofluorocarbon Interfaces

Ryo Ohmura, Yasuhiko H. Mori

Journal of Materials Science Letters (Kluwer) 17 1397-1399 1998

Research paper (scientific journal), Joint Work, Accepted

Critical Conditions for CO2 Hydrate Film to Rest on Submarine CO2 Pond Surfaces: A Mechanistic Study

Ohmura Ryo, Mori Yasuhiko H.

Environmental Science and Technology (American Chemical Society) 32 1120-1127 1998

Research paper (scientific journal), Single Work, Accepted

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