慶應義塾研究者情報データベース

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• Review of Ionic Semiclathrate Hydrates as Thermal Energy Storage Materials: Properties and Applications

  ACS Applied Engineering Materials 2023年11月

  筆頭著者

  • Access to Document (DOI)

• 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年12月

  ISSN  2045-2322

  　概要を見る

  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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• Thermodynamic analysis of hydrate-based refrigeration cycle

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

  Energy （Energy)  220 2021年04月

  ISSN  03605442

  　概要を見る

  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年02月

  ISSN  15287483

  　概要を見る

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

  Matsuura Riku, Ozawa Kazuya, Alavi Saman, Ohmura Ryo

  ACS SUSTAINABLE CHEMISTRY & ENGINEERING （ACS Sustainable Chemistry and Engineering)  8 （ 41 ） 15678 - 15684 2020年10月

  筆頭著者,  ISSN  2168-0485

  　概要を見る

  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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• 機械工学ものづくりプロジェクト

  2024年度

• 自然科学実験

  2024年度

• 理工学基礎実験

  2024年度

• 機械工学ものづくりプロジェクト

  2023年度

• 自然科学実験

  2023年度

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