Yusuke Shimoyama

Analysis of dissociation process for gas hydrates by molecular dynamics simulation

The dissociation processes of methane and carbon dioxide hydrates were investigated by molecular dynamics simulation. The simulations were performed with 368 water molecules and 64 gas molecules using NPT ensembles. The TraPPE (single-site) and 5-site models were adopted for methane molecules. The EPM2 (3-site) and SPC/E models were used for carbon dioxide and water molecules, respectively. The simulations were carried out at 270 K and 5.0 MPa for hydrate stabilisation. Then, temperature was increased up to 370 K. The temperature increasing rates were 0.1–20 TK/s. The gas hydrates dissociated during increasing temperature or at 370 K. The potential models of methane molecule did not much influence the dissociation process of methane hydrate. The mechanisms of dissociation process were analysed with the coordination numbers and mean square displacements. It was found that the water cages break down first, then the gas molecules escape from the water cages. The methane hydrate was more stable than the carbon dioxide hydrate at the calculated conditions.

Calculation of phase equilibria for the low-boiling-point compound + solvent binary systems by group-contribution equation of state

Abstract Group parameters of low-boiling-point compounds (gaseous compounds) for a group-contribution equation of state based on a hole theory previously proposed are newly determined to predict the phase equilibria for gaseous compound+solvent systems at high temperatures and pressures. The gaseous compounds studied in this work are ethane, propane, butane, carbon dioxide and ammonia. The solvents are hydrocarbons, alcohols and water. The characteristic parameters of the solid-state molar volumes and external degree of freedom required for the prediction of phase equilibria have been determined from the critical temperatures and pressures of pure compounds. The group interaction energy parameters have been determined from the experimental data of vapor pressures and phase equilibria. Good calculated results are obtained except for gaseous compound+water systems.

Effect of ion exchange rate of Y–type zeolite on selective adsorption of 2,6– and 2,7–dimethylnaphthalene isomers in supercritical carbon dioxide

Abstract The selective adsorption amounts of 2,6– and 2,7–dimethylnaphtalene (DMN) isomers dissolved in supercritical carbon dioxide (SC-CO2) on barium (Ba) ion-exchanged Y-type zeolite were measured by a constant volume method at 308.2 K. The total concentrations of 2,6– and 2,7–DMN in SC-CO2 were measured with an ultraviolet detector. The concentration ratio of 2,6– and 2,7–DMN in SC-CO2 was analyzed by gas chromatography. The separation coefficients of 2,6–DMN (2) and 2,7–DMN (3) are defined by K32 =; (Q3/C3)/(Q2/C2), where Q2 and Q3 (mol/g–zeolite) are the amounts of 2,6– and 2,7–DMN adsorbed on Y–type zeolite and C2 and C3 (mol/cm3) are the concentrations of 2,6– and 2,7–DMN in SC-CO2, respectively. The separation coefficients in SC-CO2 on Ba ion-exchanged Y–type zeolite are much higher than those in liquid octane. The separation coefficients in SC-CO2 using Ba ion-exchanged Y–type zeolite depend on ion exchange rate and amount of chloride remained on the zeolite. The separation coefficients at high pressure using Ba ion-exchanged Y–type zeolite which is higher ion exchange rate and contains lower chloride in SC-CO2 system are much higher than those using NaY–type zeolite. Therefore, the use of ion-exchanged zeolite will be useful in applications such as the design of pressure swing adsorption and supercritical chromatography processes.

CO2-Activated Adsorption: A New Approach to Dye Removal by Chitosan Hydrogel

This study focuses on development of a new adsorption technique by CO2-activated chitosan. Carbon dioxide was utilized to form the functional chemical groups of chitosan on the adsorptions of anionic dyes, Brilliant Blue FCF and Congo Red, in the aqueous solution. CO2-activated chitosan results in the dye adsorption significantly faster than that of chitosan in pure water. The adsorption capacities and removal efficiencies of the dye are increased by CO2-activated chitosan. Furthermore, the dye adsorptions on CO2-activated chitosan were investigated at various temperatures and initial dye concentrations in the aqueous solution. Interestingly, the high temperature adsorption provides the enhancement of adsorption capacities and removal efficiencies of the dye by the carbamate cross-linking of chitosan with CO2. CO2-activated chitosan was further characterized by Fourier transform infrared spectra, amino group ratio, zeta potential, and thermal gravimetric analysis. These characterizations can be used for understanding the unique adsorption of the dye on CO2-activated chitosan. Carbon dioxide-activated chitosan in this work will provide an effective operation and a clean process of dye adsorption in wastewater treatment.