A COMPARISON OF COUNTERCURRENT RECYCLE MEMBRANE CASCADES WITH SOME ONE-COMPRESSOR RECYCLE PERMEATORS FOR GAS SEPARATIONS IN TERMS OF IDEAL CROSS-FLOW STAGES

A comparison is made of countercurrent recycle membrane cascades (5-st age constant recycle and 6-stage no-mix) with continuous membrane colu mns, two-unit series, and one-unit recycle membrane modules for the en richment of O-2 from air, assuming ideal crossflow stages. The crossfl ow stage equations permit easy comparisons and give insight into the i nefficiencies associated with the ''one compressor'' module designs. F or the separation specified (production of O-2 enriched up to y(P) = 0 .983, at a rate P = 17.6, from a feed x(F) = 0.21, rate F = 100), the one compressor designs require from about 90 to 16 times more total co mpressor duty, and from about 50 to 10 times more membrane area than t he no-mix cascade design, depending on module design, to make the same separation. The one unit recycle module is least efficient, followed by the continuous membrane column, and the two unit series module. The basic reasons for the inefficiencies associated with the one compress or modules relative to the recycle cascades are explored.