論文 - 大村　亮

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年03月

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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年02月

研究論文（学術雑誌）, 共著, 査読有り

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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年01月

研究論文（学術雑誌）, 共著, 査読有り

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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年01月

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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年01月

ISSN  0021-9614

　概要を見る

<p>This paper reports experimental values of the surface tension between CO&lt;inf&gt;2&lt;/inf&gt; 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&lt;inf&gt;TBAB&lt;/inf&gt; from 0.10 to 0.40, where w&lt;inf&gt;TBAB&lt;/inf&gt; denotes the mass fraction of TBAB in the aqueous solution. These pressure-temperature-composition conditions partially fall into the stability zone of (CO&lt;inf&gt;2&lt;/inf&gt; + TBAB) semiclathrate hydrate but all data were obtained without any hydrate in the system. Surface tension decreased with increasing w&lt;inf&gt;TBAB&lt;/inf&gt; and pressure but temperature dependency was not observed. Compared to the air-TBAB aqueous solution system and CO&lt;inf&gt;2&lt;/inf&gt;-water system, the values of the surface tension were smaller.</p>

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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年

ISSN  1877-7058

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<p>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 &lt; 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.</p>

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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年

ISSN  1433-7851

　概要を見る

<p>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.</p>

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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年

ISSN  1877-7058

　概要を見る

<p>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.</p>

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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年10月

研究論文（学術雑誌）, 共著, 査読有り

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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年10月

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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年09月

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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年09月

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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年09月

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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年09月

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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年08月

ISSN  0892-7022

　概要を見る

<p>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&lt;inf&gt;2&lt;/inf&gt;O lattice and deuterated methane in H&lt;inf&gt;2&lt;/inf&gt;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.</p>

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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年07月

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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年06月

研究論文（学術雑誌）, 共著, 査読有り

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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年06月

研究論文（学術雑誌）, 共著, 査読有り

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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年05月

ISSN  1463-9076

　概要を見る

<p>Clathrate hydrates are typically stabilized by suitably sized hydrophobic guest molecules. However, it has been experimentally reported that isomers of amyl-alcohol C&lt;inf&gt;5&lt;/inf&gt;H&lt;inf&gt;11&lt;/inf&gt;OH can be enclosed into the 5&lt;sup&gt;12&lt;/sup&gt;6&lt;sup&gt;4&lt;/sup&gt; 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 5&lt;sup&gt;12&lt;/sup&gt;6&lt;sup&gt;4&lt;/sup&gt; 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.</p>

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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年04月

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