An analysis of gas separation processes of HFC-134a from gaseous mixtures with nitrogen-Comparison of two types of gas separation methods, liquefaction and hydrate-based methods, in terms of the equilibrium recovery ratio

Two types of gas separation methods, using liquefaction and gas hydrate formation, were compared in terms of the equilibrium recovery ratio for the separation of gaseous mixtures of HFC-134a and nitrogen. The equilibrium recovery ratio is defined as the molar ratio of the target component (HFC-134a, in the present case) recovered in the condensed (recovered) phase to that in the feed (vapor) phase under the equilibrium condition. The equilibrium recovery ratio was evaluated based on the phase equilibrium data for liquid-vapor and hydrate-vapor. It was found the equilibrium recovery ratio for HFC-134a is always higher for the hydrate-based separation method than that for the liquefaction separation method for the conditions of a given initial composition and pressure at 278 K or 282 K. In other words, more HFC-134a can be recovered by the hydrate-based separation than the liquefaction separation method for a given feed. The result can be explained by a simple algebraic analysis based on the phase equilibrium relationship. A two-step separation process combining the liquefaction and hydrate-based separation methods can realize the recovery of high-purity HFC-134a under reduced pressure conditions. (C) 2008 Elsevier B.V. All rights reserved.