Multicomponent gas separation by an asymmetric permeator containing two different membranes

A numerical analysis of an asymmetric permeator containing two different kinds of membranes and capable of separating a ternary feed gas mixture into three product streams has been carried out. For negligible axial pressure drops in the gas streams, equations have been developed and calculation methods illustrated for four flow patterns: cross, parallel, countercurrent and perfectly mixed. The main parameters used in the analysis are pressure ratios, the ratio of the two membrane areas and the permeabilities. Results have been presented for a 50% H₂10% CO₂40% N₂ feed with a permeator having one cellulose acetate (CA) type membrane and one silicone membrane. For both permeate streams, countercurrent achieves highest permeate qualities and requires least membrane area amongst all four flow patterns. The presence of a silicone membrane produces a richer H₂ permeate from the CA membrane than that from a CA-membrane-alone configuration. Simultaneously, an enriched CO₂ permeate is obtained from the silicone membrane. Under the ideal condition of zero pressure ratios, the asymmetric permeator has also been evaluated against the series configuration of a permeator containing a CA membrane only followed by a permeator containing only a silicone (S) membrane. The asymmetric configuration usually performs better than this series configuration for the chosen range of parameters.