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Papers - Ohmura, Ryo

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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

<p>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.</p>

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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

<p>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.</p>

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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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