Phase Equilibrium Data of Gas Hydrates Formed from a CO2 + CH4 Gas Mixture in the Presence of Tetrahydrofuran

摘要

In this work, the phase equilibrium conditions for gas hydrates formed from a CO2/CH4 gas mixture (0.4 CO2 and 0.6 CH4 in mole fraction) in the presence tetrahydrofuran (THF) were measured using the isothermal pressure search method and reported. The THF mole fractions used were 0.005, 0.01, 0.03, and 0.05 respectively. It was found that the equilibrium hydrate formation conditions obtained in the presence of THF shifted to high temperatures and low pressures as compared with those obtained using the same gas mixture in pure water. For the hydrates formed at a given temperature, the phase equilibrium pressure was observed to decrease as the THF mole fraction increased from 0.005 to 0.05. Therefore, it was confirmed that THF can be used as an effective thermodynamic promoter for CO2 separation from the CO2/CH4 gas mixture by hydrate formation. The heat of hydrate dissociation was also determined based on the measured phase equilibrium data of the gas hydrates formed from the CO2/CH4 gas mixture in the presence of THF. It was found that structure II hydrate was formed from the CO2/CH4 gas mixture in the presence of THF. Then the impact of driving force on CO2 separation from the CO2/CH4 gas mixture was investigated. The results indicated that the competition between CO2 and CH4 molecules for hydrate cage occupancy became stronger with the increase of driving force. Thus, a lower pressure at the given temperature is preferred for CO2 separation from the CO2/CH4 gas mixture by hydrate formation in the presence of THF.