Hydrate phase equilibrium in the system of (carbon dioxide + 2,2-dimethylbutane + water) at temperatures below freezing point of water

Abstract

The four-phase equilibrium conditions of (vapor+liquid+hydrate+ice) were measured in the system of (CO2+2,2-dimethylbutane+water). The measurements were performed within the temperature range (254.2 to 270.2)K and pressure range (0.490 to 0.847)MPa using an isochoric method. Phase equilibrium conditions of hydrate formed in this study were measured to be at higher temperatures and lower pressures than those of structure I CO2 simple hydrate. The largest difference in the equilibrium pressures of structure I CO2 hydrate and the hydrate formed in the present study was 0.057MPa at T=258.3K. On the basis of the four-phase equilibrium data obtained, the quintuple point for the (ice+structure I hydrate+structure H hydrate+liquid+vapor) was also determined to be T=266.4K and 0.864MPa. The results indicate that structure H hydrate formed with CO2 and 2,2-dimethylbutane is stable exclusively at the temperatures below the quintuple temperature.