Hydrate-based capture of blowing agents: Thermodynamic investigation of model gas mixtures consisting of HCFC-22, HCFC-142b, and N2

Abstract

Hydrochlorofluorocarbons (HCFCs) are representative powerful greenhouse gases that contribute significantly to global warming. As an alternative strategy for their existing separation and recovery methods, hydrate-based gas separation (HBGS) has been of great. A preliminary investigation was performed to measure the hydrate phase equilibria of pure HCFC-22, pure HCFC-142b, and two different gas mixtures of these with N2 (at molar composition ratios of 8.01:12.01:79.98 and 20.01:30.00:49.99), which is indispensable to the design of a HBGS process and determination of its operating conditions. Hydrate dissociation enthalpies of the investigated systems were calculated from the measured equilibrium data using the Clausius-Clapeyron equation, and their values were 82.12 (HCFC-22), 153.65 (HCFC-142b), 127.90 (HCFC-22 8.01%), and 133.51 (HCFC-22 20.01%) kJ/mol, respectively. Their crystal structures were determined using powder X-ray diffraction, and results revealed that HCFC-22 merely formed structure I hydrate. Kinetic hydrate formation tests were carried out with the two different gas mixtures, and the compositions of the vapor and hydrate phases were examined. The hydrate nucleation and separation performance were profoundly affected by the initial system pressure, proven by showing the shortest induction time and the highest separation factor for HCFCs.