Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.fuel.2020.119747

researchmap

Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

Hydrate-based gas separation is often investigated using batch or semi-batch operations. To increase the throughput of the gas mixture without increasing the apparatus volume, it is preferable to perform a continuous operation of hydrate-based gas separation. Therefore, we proposed a flow-type apparatus for performing continuous formation with passing gaseous mixture and subsequently decomposition with passing gas hydrate particles. Characteristics of multiple fluid and heat and mass transfer of hydrate slurry are essential for the efficient operation of the apparatus. In this study, we focused on heat transfer characteristics in the presence of bubbles in water and surfactant solution. First, an apparent overall heat transfer coefficient under pressure during steady operation of the apparatus was calculated on a simple assumption. Next, to control the hydrate amount and position of hydrate-decomposition and hydrate-formation in the apparatus, we focused on the temperature profile of the inside fluid. A heat transfer model using heat balance of defining heat of hydrate-formation and heat transfer of agitation of fluid was made for hydrate-based gas separation apparatus. To evaluate the validity of the heat transfer model, a calculation value is compared with the experimental value.

DOI： 10.1051/matecconf/202133304001

researchmap

Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

Hydrated-based gas separation is a method capable of selectively separating and recovering greenhouse gases. Although a conventional hydrate-based gas separation apparatus is a batch or a semi-batch system, continuous operation is preferable to increase the throughput of gas without changing the apparatus volume. Recently, we proposed a flow type apparatus to allow continuous operation of hydrate formation (absorption) and subsequent decomposition (desorption). The aim of this study is to investigate the mass transfer characteristics of the continuous apparatus using the HFC134a-N2 mixed gas system. The volumetric mass transfer coefficient was calculated especially during a steady state of gas absorption. Besides, we compared mass transfer performance between the hydrate-based gas absorber and a conventional bubble column. Sodium dodecyl sulfate was used as a hydrate dispersant. In the flow type apparatus, the gas-liquid contact was good and the hydrate slurry state was observed during hydrate formation. In the surfactant solution, the volumetric mass transfer coefficient increased in comparison with that in water. The volumetric mass transfer coefficient with hydrate was higher than that of the bubble column. These results suggest that hydrate formation improves gas absorption performance.

DOI： 10.1051/matecconf/202133304002

researchmap

Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

We are focusing on the practical use of methane hydrate. For recovery and use of it as an energy resource, it is necessary to consider the possibility of clogging in the recovery pipe due to the rehydration of bubbles. The purpose of this research was to observe experimentally and evaluate theoretically the decomposition behavior of hydrate sedimentary layer and the rising behavior of bubbles generated by hydrate decomposition. Chlorodifluoromethane was used as a low pressure model gas of methane. Hydrate sedimentary layer was produced by cooling and pressurizing water in countercurrent contact with gas using a hydrate formation recovery device. The recovered hydrate was decomposed by the heating or depressurization method, without flowing water. Two theoretical rising velocities were derived from the theoretical value with using the Navier-Stokes equation or the values in consideration of the bubble shape and hydrate film existence. The experimental rising velocities of small spherical bubbles radius agreed well with the theoretical value by the Navier-Stokes equation. The relatively large elliptical bubbles showed a behavior close to the theoretical value of bubble with hydrate film. Under the pressure and temperature conditions closer to the hydrate equilibrium line, almost no generated bubbles could be identified visually.

DOI： 10.1051/matecconf/202133302007

researchmap

Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

We are focusing on the practical use of methane hydrate. For recovery and use of it as an energy resource, it is necessary to consider the possibility of clogging in the recovery pipe due to the rehydration of bubbles. The purpose of this research was to observe experimentally and evaluate theoretically the decomposition behavior of hydrate sedimentary layer and the rising behavior of bubbles generated by hydrate decomposition. Chlorodifluoromethane was used as a low pressure model gas of methane. Hydrate sedimentary layer was produced by cooling and pressurizing water in countercurrent contact with gas using a hydrate formation recovery device. The recovered hydrate was decomposed by the heating or depressurization method, without flowing water. Two theoretical rising velocities were derived from the theoretical value with using the Navier-Stokes equation or the values in consideration of the bubble shape and hydrate film existence. The experimental rising velocities of small spherical bubbles radius agreed well with the theoretical value by the Navier-Stokes equation. The relatively large elliptical bubbles showed a behavior close to the theoretical value of bubble with hydrate film. Under the pressure and temperature conditions closer to the hydrate equilibrium line, almost no generated bubbles could be identified visually.

DOI： 10.1051/matecconf/202133302007

researchmap

Publishing type：Research paper (scientific journal)  

© 2019 The transient heat and mass transfer near a methane hydrate decomposition interface were quantitatively measured to evaluate the rate-determining factors of dissociation with high spatiotemporal resolution. In this study, we proposed a measurement system for the dissociation phenomenon near the hydrate interface, and the rate-determining step of the dissociation phenomenon was discussed in terms of the experimental results and numerical simulation using a dissociation model. The hydrate was generated around a water-like film under temperature of 274 K and pressure of 4.8 MPa of mixed gas comprising methane and helium in a temperature and pressure controlled system. A high-speed phase-shifting interferometer was used to measure the interfacial transient heat and mass transfer. In the present study, transient variations in the optical path length difference caused by the variation in the density field near the hydrate interface were visualized with temporal and spatial resolutions of 1 ms and 3.88 μm/pixel, respectively. The measured values were compared with the results of numerical simulations, assuming that the mass flux of methane was a function of the activation energy of dissociation. The comparison showed that the experimentally measured values exhibited similar tendency as the values estimated using the activation energy of approximately 60,000 J/mol. This result was also confirmed from the interface shape variation of the hydrate. Finally, the dissociation phenomenon of the hydrate was estimated as the rate-determining step of the reaction by using our special interferometer system.

DOI： 10.1016/j.ijheatmasstransfer.2019.119191

Scopus

researchmap

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ces.2019.115361

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cherd.2020.01.031

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cherd.2019.08.007

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The objective of this work was to investigate diffusion phenomena in methane clathrate hydrates during depressurization that lead to their dissociation. A thermodynamic mass transfer model is proposed that considers cage occupancy in structure I clathrate hydrates and methane diffusion from both S-cages (dodecahedron: 12 pentagons) and M-cages (tetradecahedron: 12 pentagons, 2 hexagons). Methane occupancies during dissociation were measured in situ with Raman spectroscopy with a newly constructed optical system and data were estimated with Langmuir constants calculated by assuming a spherically symmetric cell potential. Model results were in agreement with experimentally-measured changes in average occupancy with time, so that dissociation kinetics at the interface were concluded to be strongly related to both methane diffusion and cage occupancy. Dissociation kinetics of methane hydrate can be reliably estimated with the proposed model. The proposed model is applicable to the study of methane hydrate dissociation-limited mechanisms or to larger-scale geological systems being used to estimate gas production rates. (C) 2019 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.fluid.2019.02.004

Web of Science

Scopus

researchmap

Other Link： http://orcid.org/0000-0002-8836-1294

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institution of Chemical Engineers  

Many studies have been conducted on the application of hydrate-based gas separation to recover or reduce greenhouse-gas emissions. We evaluated the effects of hydrate-slurry decomposition conditions, specifically depressurization and heating, on gas recovery and separation, by using mixtures of refrigerants R22 or R134a with N2 as models of a greenhouse gas and a low-pressure gas, respectively. The recoveries of R22 and R134a were assessed and N2 was released preferentially during the earlier stage of decomposition, such that the highest N2 recovery rate was obtained during that time span. In contrast, the recovery rates of the target gases increased gradually with time up to maximum values. Pressure and temperature had a minimal effect on the N2 recovery rate, whereas the target gas-recovery rates were highly dependent on decomposition pressure and temperature values. The maximum separation factors were approximately 50 for R22 and 20 for R134a. A mechanism for the variation in separation factor is proposed, based on an analysis of gas generation as a function of decomposition time and fluid temperature.

DOI： 10.1016/j.cherd.2018.04.030

Scopus

researchmap

Other Link： http://orcid.org/0000-0002-8836-1294

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Winterization is one means of improving the low temperature flow properties of biodiesel fuel, by the separation of saturated FAMEs. Additives are also employed to improve separation in the winterization process by modifying the crystallization behavior. This process is referred to as additive winterization. In a previous study, we investigated a novel additive winterization method in which FAMEs are separated without agitation during cooling, allowing improved separation of saturated FAME and unsaturated FAME mixtures. This method is both facile and energy-efficient because vacuum filtration is not required. In this study, we examined the effects of additives (sorbitan mono fatty acids) and agitation on the separation of saturated FAMEs from saturated and unsaturated FAME mixtures via winterization. The additive winterization process resulted in significant improvements in the cloud points of the FAME mixtures following a single separation run, with the cloud point being decreased by 8 K under optimum conditions. In contrast, winterization based on agitation required at least two cycles of sequential cooling, agitation and filtration to obtain similar results. This study therefore highlights the potential of additive winterization using sorbitan mono fatty acid esters to enhance the low-temperature flow properties of biodiesel fuels based on a simple process with reduced energy expenditures.

DOI： 10.1016/j.fuel.2017.11.066

Web of Science

Scopus

researchmap

Other Link： http://orcid.org/0000-0002-8836-1294

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

This work investigated the removal of saturated fatty acid methyl esters (FAMEs) from FAME mixtures by winterization, employing additives as solid-liquid phase separation improvers during the cooling process. Model mixtures were prepared by blending saturated FAMEs (methyl palmitate and methyl stearate) and an unsaturated FAME (methyl oleate). Sorbitan monopalmitate (Span40) and Sorbitan monostearate (Span60) were selected as separation improvers because their molecular structures were close to those of the saturated FAME in the model mixture. These additives were found to improve the solid-liquid phase separation of FAME mixtures. Four different solid phases were observed during winterization, depending on the additive concentration: a solid wax, a solid incorporating small amounts of liquid, a large crystal agglomeration, and a slurry of fine particles. The formation of the large crystal agglomeration made it easier to perform solid-liquid separation via decantation, such that the saturated FAME was readily removed from the liquid phase when employing the optimum additive concentration. When the additive had an equal or longer carbon chain length compared with the saturated FAME, a greater extent of low temperature separation was obtained. These results will be helpful to the future development of the additive winterization process. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.fuel.2016.10.124

Web of Science

Scopus

researchmap

Other Link： http://orcid.org/0000-0002-8836-1294

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

We assessed a simple thermodynamic model, with the aim of identifying biodiesel fuel cloud point (CP) improving additives, by predicting the CP values of fatty acid methyl esters with additives. The results showed that the molar mass of the additive has a significant effect in terms of improving the CP; the melting point and fusion enthalpy of the additive, however, produce lesser effects. On the basis of these results, we selected the additives tert-butyl alcohol, 2-butanol, cineol, 2-decanol, 2-decanone and oleyl alcohol, and examined their effects on the CP of a model biodiesel fuel (a methyl oleate and methyl palmitate mixture). The same trials were carried out using fatty acid methyl ester mixtures derived from commercial cooking oils. As predicted, the selected test additives decreased the sample CP values, with the optimum reduction obtained when using 10 wt.% of the additive. The results demonstrate that additives capable of improving the CP can be readily screened using a simple thermodynamic model. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.fuel.2015.12.053

Web of Science

Scopus

researchmap

Other Link： http://orcid.org/0000-0002-8836-1294

Language：Japanese   Publisher：The Japan Institute of Energy  

<p>In this work, a model that can be used in large-scale simulations was developed for studying the dissociation of methane hydrate. In the model, two mechanisms were assumed: (i) dissociation of methane hydrate as as a concentration driving force difference and (ii) decomposition of hydrate host cage of the methane hydrate according to a chemical potential driving force ignoring heat effects of the endothermic reaction. Experimental data of decomposition rates at 278 K, 4.39 MPa were correlated by the model assuming that (i) and (ii) occur in parallel using an effective rate constant of decomposition K as a fitting parameter. As a result, the rate constant of decomposition <i>K</i> was estimated to be 1.73 × 10^-9 at 278 K.</p>

DOI： 10.20550/jietaikaiyoushi.25.0_30

CiNii Article

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Gas adsorption rates of H-2, CO2, and H-2-CO2 gas mixture (H-2/CO2=3.4) with tetra-n-butyl ammonium salt (bromide, chloride, and fluoride) semi-clathrate hydrate particles were measured at 269 K to assess their properties for gas separation. Equilibrium gas occupancies in the S-cages of the particles were in order of (high to low) for hexagonal structure-I, tetragonal structure-I, and superlattice of cubic structure-I structures with the maximum fractional occupancy by CO2 being about 40%. The CO2 diffusion rate depended on the anion size of the salt, which is attributed to distortion of the S-cage that is close to the molecular size of CO2. Simulations of semi-clathrate hydrate particles with theory showed that H-2/CO2 selectivities could be as high as 36 (3.0 mol% TBAF) and that selectivities for an ideal membrane (3.3 mol% TBAF) could be &gt;100 (269 K, 0.3-4.5 MPa). Semi-clathrate hydrates have wide application as separation media for gas mixtures. (c) 2014 American Institute of Chemical Engineers AIChE J, 61: 992-1003, 2015

DOI： 10.1002/aic.14689

Web of Science

Scopus

researchmap

Other Link： http://orcid.org/0000-0002-8836-1294

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Adsorption rates are reported for H-2-tetrahydroluran (THE), H-2-THF (D2O), H-2-THF-d8, H-2-furan, H-2-cyclopentane (CP) and H-2-tetrahydrothiophene (THT) binary clathrate hydrates at temperatures of 265273 K and pressures of 4-10 MPa. Adsorption rates of H-2-furan and H-2-6.8 mol% THE binary clathrate hydrates were the fastest among these binary clathrate hydrates. The lattice constant of hydrates were determined to analyze the adsorption data with a newly proposed multiple adsorption resistance (MAR) model. The effect of the non-included additive guest molecule on hydrogen adsorption rate was important because they promoted formation of pores and grain boundaries when hydrate particles formed. Activation energies, Delta E-Da, for H-2 diffusion into clathrate hydrates calculated from the Arrhenius plots depended on the hydrate guest additive and were determined to be: 18.0 kJ/mol (6.2 mol% THF), 30.7 kJ/mol (5.6 mol% THF), and 100 kJ/mol (cyclopentane). Based on the Delta E-Da) values, H-2 diffusion pathway in hydrate particles depends on the clathrate hydrate formation process and the interactions between guest additive molecule and the host molecule. (C) 2014 Elsevier Ltd. All rights reserved,

DOI： 10.1016/j.ces.2014.01.001

Web of Science

Scopus

researchmap

Other Link： http://orcid.org/0000-0002-8836-1294

Language：English  

水素精製時におけるガス分離プロセス構築を対象とし，添加第四級アンモニウム塩のアニオンがH&lt;sub&gt;2&lt;/sub&gt;およびCO&lt;sub&gt;2&lt;/sub&gt;存在下におけるセミクラスレートハイドレートの相平衡およびガス吸着・拡散特性に与える影響について検討するとともに，分離媒体としての有用性を評価した．

researchmap

Language：Japanese   Publisher：The Japan Institute of Energy  

In this work, the phase behavior of CO_2 + tetra-n-butyl ammonium fluoride(TBAF) semi-clathrate hydrates with added Na_2CO_3 or NaCl was measured and correlated with a modified van der Waals and Platteeuw model and Pizer model for the purpose of developing a CO_2-H_2 gas separation process. When Na_2CO_3 (0.66 mol/L) was added, the pressure-temperature solid-liquid-vapor (PT-SLV) equilibrium curve shifted to lower temperatures by around 4 K compared with that of CO_2-TBAF. When NaCl(0.24 mol/L) was added, the PT-SLV curve has not shifted little. The data could be correlated by the model to within 10.4% in pressure. The model allows the estimation of the stability of the semi-clathrate hydrates in presence of electrolytes.

DOI： 10.20550/jietaikaiyoushi.23.0_40

CiNii Article

CiNii Books

researchmap

Language：Japanese   Publisher：The Japan Institute of Energy  

In this work, an effect of anion (Br^-, CI^- and F^-) of tetra-n-butyl ammonium (TBA) salts on the H_2 and CO_2 adsorption and diffusional characteristics of semi-clathrate hydrate was investigated with multiple adsorption resistance (MAR) model for the purpose of gas separation. The equilibrium H_2 occupancy in the S-cage depended on the semi-clathrate hydrate structure. The equilibrium CO_2 occupancy in S-cage depended not only on that but also on the TBA salt for TS-I strucure. The apparent diffusion coefficients for H_2 systems were larger than those for CO_2 systems. The H_2/CO_2 selectivities for 3.0 mol% TBAF semi-clathrate hydrate was the highest among TBA salt semi-clathrate hydrate.

DOI： 10.20550/jietaikaiyoushi.23.0_44

CiNii Article

CiNii Books

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

In this work, gas adsorption equilibria for H2 and for CO2 with THF clathrate hydrate particles and with tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate particles (250-355μm) were measured. The structures of the TBAB semi-clathrate hydrates were confirmed with Raman spectroscopy and with differential scanning calorimetry. The THF clathrate hydrate particles had the largest adsorption (ca. 13.7mmol-H2/mol-host) at 269K among all of the hydrates studied. H2 adsorption at 269K for 2.6mol% TBAB semi-clathrate hydrate (type-B rich) was ca. 6.9mmol-H2/mol-host and that for 3.7mol% TBAB semi-clathrate hydrate (type-A rich) was ca. 3.4mmol-H2/mol-host. For CO2, THF clathrate hydrate had higher adsorption capacity (ca. 68.5 mmol-CO2/mol-host) than type-A (ca. 16.3 mmol-CO2/mol-host) or type-B (ca. 29.0 mmol-CO2/mol-host) semi-clathrate hydrate. Type-B TBAB semi-clathrate hydrate had a larger Langmuir constant ratio (CCO2/CH2) than that of THF hydrate. The selectivity of type-B TBAB semi-clathrate hydrate implied by the Langmuir constant ratio can be expected to be large, however the results need to be confirmed with gas mixtures and other conditions including effect of semi-clathrate hydrate particle size. © 2013 .

DOI： 10.1016/j.fluid.2013.05.027

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Replacement reactions in clathrate hydrates, for which CO2 is used to replace methane gas trapped in inclusion compounds in the deep sea or permafrost areas, have gained growing attention as a possible method to sequester CO2 and recover natural gas. This review examines research progress in the replacement reactions and analytical methods with special focus on laboratory studies. Methane hydrate dissociation enthalpies, carbon dioxide hydrate dissociation enthalpies, methane hydrate thermal conductivities and thermal diffusivities are tabulated. Methods used to study the CH4-CO2 replacement reaction include material balance (MB), MB with particle size analyzer, MB and Raman, NMR, and magnetic resonance imaging. New analytical methods such as thermo-Raman should be explored in the future to develop a localized picture of the microscopic replacement mechanism including water molecule movement. Combination of these data with molecular simulations will allow new macroscopic models to be developed for use with practical processes for unconventional natural gas. © 2013 Taiwan Institute of Chemical Engineers.

DOI： 10.1016/j.jtice.2013.03.010

Scopus

researchmap

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Phase equilibrium data for H-2 + tetrahydrofuran (THF) and H-2 + cyclopentane (CP) binary clathrate hydrate systems were determined from temperature and pressure measurements with a newly designed semimicro (approximate to 0.78 cm(3)) cell. The range of conditions studied for the two systems was at pressures from (2 to 14) MPa and at temperatures from (278 to 285) K. Inclusion characteristics of the hydrogen molecules for both systems were similar according to their Raman spectra. The measured data for the H2 THF binary clathrate hydrate system were in agreement with some of the data in the literature. New phase equilibrium data and Raman spectroscopy analyses for the H-2 + CP binary clathrate hydrate system are reported. The dissociation enthalpies determined from data in the pressure range from (8 to 14) MPa were (212 and 220) kJ.mol(-1) for the H-2 + THF and H-2 + CP binary clathrate hydrate systems, respectively.

DOI： 10.1021/je900767h

Web of Science

Scopus

researchmap

Language：Japanese   Publisher：公益社団法人 化学工学会  

DOI： 10.11491/scej.2010f.0.150.0

CiNii Article

researchmap

Language：English  

Rheological properties of tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate slurries with polyvinyl alcohol (PVA) were measured with a single-cylinder rotational viscometer for the purpose of evaluating the effect of polymer dispersants. Concentration and degree of polymerization (DP) of PVA dispersants on aggregation of hydrate slurries were investigated. Dispersibility and dispersion stability of hydrate slurries with 0.86 wt% PVA (DP of 2000) were the highest among the PVA concentrations examined. Long-chain length PVA readily causes cross-linking aggregation but improves hydrate slurry dispersion stability.

researchmap

Language：English  

Additive winterization processes using sorbitan monopalmitate and sorbitan monostearate were compared with a conventional agitation winterization for the separation of saturated FAMEs from a mixture of saturated and unsaturated FAMEs. The additive winterization process led to greater improvements in the low-temperature flow properties of the FAME mixtures by a single stage. Furthermore, the agitation winterization required at least three cycles of sequential cooling, agitation and filtration to obtain similar results. This study therefore highlights the potential of additive winterization for improving the low-temperature flow properties of biodiesel fuels containing sorbitan mono fatty acid esters as a simple, energy-saving process.

researchmap

Language：Japanese   Publisher：公益社団法人 日本工学教育協会  

CiNii Article

CiNii Books

researchmap

Language：English  

Characteristic structural changes that occur in hydrates and semi-clathrate hydrates are important for understanding hydrate properties for gas separation applications. In this work, gas adsorption equilibria for H&lt;sub&gt;2&lt;/sub&gt; and for CO&lt;sub&gt;2&lt;/sub&gt; with THF clathrate hydrate particles and with tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate particles were measured. The THF clathrate hydrate particles had the largest adsorption (ca. 15.0 mmol-H&lt;sub&gt;2&lt;/sub&gt;/mol-H&lt;sub&gt;2&lt;/sub&gt;O) among all of the hydrates studied. The TBAB semi-clathrate hydrates had two types of structures, type A and type B, as confirmed by differential scanning calorimetry. It was found that H&lt;sub&gt;2&lt;/sub&gt; adsorption for 2.6 mol% TBAB semi-clathrate hydrate (type B-rich) was larger than that for 3.7 mol% TBAB semi-clathrate hydrate (type A-rich) at the beginning of the isothermal isobaric conditions for H&lt;sub&gt;2&lt;/sub&gt; gas. The capture cavity structure for H&lt;sub&gt;2&lt;/sub&gt; or CO&lt;sub&gt;2&lt;/sub&gt; is demonstrated experimentally to be different between type A and type B TBAB semi-clathrate hydrates by material balance.

researchmap

J-GLOBAL

researchmap

Language：English  

Formation rates are reported for H&lt;sub&gt;2&lt;/sub&gt;-THF, H&lt;sub&gt;2&lt;/sub&gt;-THF (D&lt;sub&gt;2&lt;/sub&gt;O), H&lt;sub&gt;2&lt;/sub&gt;-THF-d8, H&lt;sub&gt;2&lt;/sub&gt;-furan, H&lt;sub&gt;2&lt;/sub&gt;-CP and H&lt;sub&gt;2&lt;/sub&gt;-tetrahydrothiophene (THT) binary clathrate hydrates at 269 K, at 8.2 MPa. Formation rates of<br />
H&lt;sub&gt;2&lt;/sub&gt;-furan binary clathrate hydrate was fastest among these binary clathrate hydrates. The lattice constant of hydrates were determined and used to analyze the data with a newly proposed two stage model. Hydrogen formation rate differences between the binary clathrate hydrates can be described by the model.

researchmap

Language：English  

The phase equilibrium of the H&lt;sub&gt;2&lt;/sub&gt; + cyclopentane binary clathrate hydrate is important because cyclopentane (CP) has been shown to reduce the equilibrium storage pressures similar to that of tetrahydrofuran (THF). In this work, we apply correlations for the H&lt;sub&gt;2&lt;/sub&gt; + CP binary clathrate hydrate system based on the Gibbs free energy and the Kihara potential. The correlation is also applied to the H2 + THF binary clathrate hydrate system and compared with literature results. It was found that the models could correlate both H&lt;sub&gt;2&lt;/sub&gt; + CP and H&lt;sub&gt;2&lt;/sub&gt; + THF sufficiently. From the calculated hydrogen occupancies and the Langmuir constants of CP and THF, the relationship between hydrate dissociation enthalpy and hydrogen occupancy was studied. The hydrate dissociation enthalpy varied according to phase equilibrium conditions at low pressure. The Langmuir constant of CP was lower than that of THF which implies that the formation of CP clathrate hydrate is more difficult to form than THF clathrate hydrate. As hydrogen occupancies became higher, the hydrate dissociation enthalpies of H&lt;sub&gt;2&lt;/sub&gt; + hydrocarbon binary clathrate hydrate approached a constant value.

researchmap

Language：Japanese  

<p>In this work, a model that can be used in large-scale simulations was developed for studying the dissociation of methane hydrate. In the model, two mechanisms were assumed: (i) dissociation of methane hydrate as as a concentration driving force difference and (ii) decomposition of hydrate host cage of the methane hydrate according to a chemical potential driving force ignoring heat effects of the endothermic reaction. Experimental data of decomposition rates at 278 K, 4.39 MPa were correlated by the model assuming that (i) and (ii) occur in parallel using an effective rate constant of decomposition K as a fitting parameter. As a result, the rate constant of decomposition <i>K</i> was estimated to be 1.73 × 10^-9 at 278 K.</p>

researchmap

Language：Japanese  

<p>In this work, CO₂ sorption by tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate (SCH) slurries in the absence and in the presence of polyvinyl alcohol (PVA) and sodium dodecyl sulfate (SDS) dispersants was investigated. CO₂ sorption was measured with a newly-developed bubble column reactor. CO₂ sorption amount for SCH slurry was about 3.2 mmol-CO₂/mol-water at 0.8 MPa (He/CO₂ = 4) in the absence of dispersants. Rheological behavior of the SCH slurries was studied. SDS caused a reduction in the SCH slurry viscosity, whereas PVA caused an increase in slurry viscosity. The SCH slurries with the dispersants were determined to be Bingham plastic.</p>

researchmap

Language：Japanese  

researchmap

Language：Japanese  

In this work, an effect of anion (Br^-, CI^- and F^-) of tetra-n-butyl ammonium (TBA) salts on the H_2 and CO_2 adsorption and diffusional characteristics of semi-clathrate hydrate was investigated with multiple adsorption resistance (MAR) model for the purpose of gas separation. The equilibrium H_2 occupancy in the S-cage depended on the semi-clathrate hydrate structure. The equilibrium CO_2 occupancy in S-cage depended not only on that but also on the TBA salt for TS-I strucure. The apparent diffusion coefficients for H_2 systems were larger than those for CO_2 systems. The H_2/CO_2 selectivities for 3.0 mol% TBAF semi-clathrate hydrate was the highest among TBA salt semi-clathrate hydrate.

researchmap

Language：Japanese  

In this work, the phase behavior of CO_2 + tetra-n-butyl ammonium fluoride(TBAF) semi-clathrate hydrates with added Na_2CO_3 or NaCl was measured and correlated with a modified van der Waals and Platteeuw model and Pizer model for the purpose of developing a CO_2-H_2 gas separation process. When Na_2CO_3 (0.66 mol/L) was added, the pressure-temperature solid-liquid-vapor (PT-SLV) equilibrium curve shifted to lower temperatures by around 4 K compared with that of CO_2-TBAF. When NaCl(0.24 mol/L) was added, the PT-SLV curve has not shifted little. The data could be correlated by the model to within 10.4% in pressure. The model allows the estimation of the stability of the semi-clathrate hydrates in presence of electrolytes.

researchmap

Language：Japanese  

researchmap