Takashi Makino

Stability boundaries of gas hydrates helped by methane—structure-H hydrates of methylcyclohexane and cis-1,2-dimethylcyclohexane

The four-phase coexistence curves for the structure-H hydrates of methylcyclohexane and cis-1,2-dimethylcyclohexane in the presence of methane are measured in the temperature range 274.09–288.29K and pressure range 1.42–8.89MPa. Very large pressure reductions from the pure methane hydrate are observed by forming structure-H hydrates. The present investigation on the trans-1,2-dimethylcyclohexane system reveals that the limit of the largest-cage occupancy for the structure-H hydrate is laid between the 1,2-dimethylcyclohexane stereo-isomers.

Physical and CO2-Absorption Properties of Imidazolium Ionic Liquids with Tetracyanoborate and Bis(trifluoromethanesulfonyl)amide Anions

Ionic liquids with tetracyanoborate ([TCB]−) and bis(trifluoromethanesulfonyl)amide ([Tf2N]−) anions generally have low viscosities and high CO2 capacities, and thus they are attractive solvents for CO2-related applications. Herein, we have investigated physical and CO2-absorption properties of 1-ethyl-3-methylimidazolium tetracyanoborate ionic liquid ([emim][TCB]) to discuss the anion effects of [TCB]− in comparison with the previous results of [emim][Tf2N]. The density, viscosity, electrical conductivity, and isobaric molar heat capacity were measured as a function of temperature at atmospheric pressure. [emim][TCB] has both lower density and isobaric molar heat capacity than [emim][Tf2N]. [emim][TCB] shows superior transport properties (lower viscosity and higher electrical conductivity) compared to [emim][Tf2N], whereas the Walden plots of molar conductivity against fluidity (reciprocal of viscosity) have smaller values in [emim][TCB] than in [emim][Tf2N] at certain fluidities. The high-pressure CO2 solubilities were also determined in [emim][TCB]. The mole fraction scaled solubility of CO2 in [emim][TCB] is slightly larger than that in [emim][Tf2N] at certain pressures and temperatures. The former ionic liquid shows much higher molarity scaled solubility of CO2 than the latter because of the smaller molar volume. It is suggested that both anions have similar strength of intermolecular interaction with CO2 and comparable changes in the solvent structure between neat and CO2 solution, in view of the thermodynamic parameters of dissolution.

Study on Prompt Methane Hydrate Formation Derived by Addition of Ionic Liquid

Aims: The objective of this study is to establish the fundamental model on methane hydrate formation and to accelerate the rate of methane hydrate formation with a small amount of ionic liquid and to investigate the effect of ionic liquid on hydrate formation. Study Design: Experimental study containing modeling. Place and Duration of Study: The present study was held between April 2010 and February 2012 at Division of Chemical Engineering, Department of Materials Engineering Science, Osaka University. Methodology: Methane hydrate formation was modelized based on the driving force, fugacity difference before and after hydrate formation. BMIM-hexafuorophosphate (BMIMPF6) was adopted as a representative of 1-butyl-3-methylimidazolium (BMIM) salts. The temperature dependence of methane hydrate formation rate was investigated and activation energy of hydrate formation was evaluated for the pure water and BMIM-PF6 aqueous solution systems. Research Article American Chemical Science Journal, 2(3): 100-110, 2012 101 Results: An addition of small amount of BMIM-PF6 is able to accelerate the methane hydrate formation. The pseudo-first order reaction model is applicable to the methane hydrate formation in both the pure water and BMIM-PF6 aqueous solution systems. The activation energies of methane hydrate formation are large negative values in the both systems, that is, the methane hydrate formation process is considered to be composed of the precursory hydration and succeeding hydrate formation. A very small amount of BMIMPF6 seems to change the interfacial energy between guest molecules and precursor or initial hydrate particles without the change of the activation energy for overall methane hydrate formation.

Isothermal Phase Equilibria and Cage Occupancies for CH4 + CHF3 Mixed-Gas Hydrate System

Isothermal phase equilibria for the CH 4 + CHF 3 mixed-gas hydrate system were investigated under three-phase equilibrium states at 291.1 K by using gas chromatography. In addition, the single-crystals of mixed-gas hydrate were analyzed by means of Raman spectroscopy. One of the most important findings in the present study is that there is no hy- drate-structural transition, as the composition of mixed gas was varied at 291.1 K in the CH 4 + CHF 3 mixed-gas hydrate system.

Nucleophilic reactions of bromocyclopentane in the structure-H methane + bromocyclopentane mixed hydrate system at high pressures.

Thermodynamic stability boundary in the structure-H methane + bromocyclopentane mixed hydrate system was measured at pressures from 20 to 100 MPa. The thermodynamic stability boundary of the methane + bromocyclopentane mixed hydrate exhibits anomalous behavior under conditions at high pressures and high temperatures. This phenomenon is due to the elimination and substitution reactions of bromocyclopentane to cyclopentene and cyclopentanol, respectively. The nucleophilic reactions of bromocyclopentane are mainly advanced in the liquid bromocyclopentane-rich phases, while it is restrained when bromocyclopentane is enclathrated in hydrate cage.