Solution-Diffusion for Gas Mixtures

If the mass-transfer resistances in the two fluid films are negligible, 

The ideal dense membrane has a high permeance for the penetrant molecules and a high selectivity between the components to be separated. The selectivity is expressed in terms of the separation factor, aAB, defined similarly to the relative volatility in distillation  

For the separation of a binary mixture of species A and B, in the absence of external film mass-transfer resistances, the transport fluxes are given by equation (9-9) as 

When no sweep gas is used, the ratio of NA to NB fixes the composition of the permeate so that 

NA yA HaDa xaPf yAPP) nb yB HbDb xbPf ysPp) 

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