Differential permeation, with permeate membrane area

The gas composition and pressure differential become very important when the more permeable gas in the feed has a low concentration. Since the partial pressure of the fast component on the permeate side cannot exceed its partial pressure on the feed side, high feed gas pressures and low permeate pressures are required to obtain efficient separations even with high separation factors. The differential pressure across the membrane relates directly to the membrane area required. Compression costs on the other hand are a function of pressure ratio. Therefore, operation at high pressure with a substantial pressure differential across the membrane but with a reasonably low pre.ssure ratio, is economically advantageous where recompression of the permeate is requited. 

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