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 N-2 as models of a greenhouse gas and a low-pressure gas, respectively. The recoveries of R22 and R134a were assessed and N-2 was released preferentially during the earlier stage of decomposition, such that the highest N-2 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 N-2 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. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.