Effects of hydrate-slurry decomposition conditions on gas generation and recovery performance

Many studies have been conducted on the application of hydrate-based gas separation to recover or reduce greenhouse-gas emissions. We evaluated the effects of hydrate-slurry decomposition conditions, specifically depressurization and heating, on gas recovery and separation, by using mixtures of refrigerants R22 or R134a with N2 as models of a greenhouse gas and a low-pressure gas, respectively. The recoveries of R22 and R134a were assessed and N2 was released preferentially during the earlier stage of decomposition, such that the highest N2 recovery rate was obtained during that time span. In contrast, the recovery rates of the target gases increased gradually with time up to maximum values. Pressure and temperature had a minimal effect on the N2 recovery rate, whereas the target gas-recovery rates were highly dependent on decomposition pressure and temperature values. The maximum separation factors were approximately 50 for R22 and 20 for R134a. A mechanism for the variation in separation factor is proposed, based on an analysis of gas generation as a function of decomposition time and fluid temperature.