Phase Equilibrium Studies of Tetrahydrofuran (THF) + CH4, THF + CO2, CH4 + CO2, and THF + CO2 + CH4 Hydrates

The hydrate phase equilibrium behaviors of tetrahydrofuran (THF) + CH4, THF + CO2, CH4 + CO2, and THF + CO2 + CH4 were investigated over wide ranges of temperature, pressure, and concentration. The dissociation conditions of THF + CH4 and THF + CO2 hydrates were shifted to lower pressures and higher temperatures from the dissociation boundaries of pure CH4 and pure CO2 hydrates. X-ray diffraction results revealed that the CH4 + CO2 and THF + CO2 + CH4 hydrates prepared from a CH4/CO2 (50:50) gas mixture formed structure I and II clathrate hydrates, respectively. Raman measurements provided detailed information regarding the cage occupancy of CH4 and CO2 molecules encaged in the hydrate frameworks. For the CH4 + CO2 hydrates, the concentrations of CO2 in the hydrate phase were higher than those in the vapor phase. In contrast, for the THF + CO2 + CH4 hydrates, the concentrations of CO2 in the hydrate phase were lower than those in the vapor phase.