Separation

The separation factor for a binary mixture of gases A and B , aA/B, is the ratio of the compositions of components A and B in the permeate relative to the composition ratio of these components in the retentate:

aA/B = [cA/cB]Permeate / [cA/cB]Retentate

where c is the mole fraction of the gas specie. The separation factor can also be defined in terms of concentrations in the permeate and retentate since only ratios are involved.

The separation factor for PermSelect® silicone membranes  for various binary gas mixtures simulating different feed gas compositions is presented in the table below. The separation factor was measured at different feed pressures, with 0 psig permeate pressure and at a temperature of 23ºC.  The feed gas flowed inside the hollow fibers and the feed flowrate was maintained much greater than the permeate flowrate. Moreover, it was assumed that the feed and retentate pressure were maintained essentially equal. Thus the separation factors can be used to predict permeate composition using the equation above and assuming these conditions are valid in the intended application.

WARNING.  Separation factors listed below were determined using special test modules capable of tolerating high pressures. Users of PermSelect® membrane modules should not exceed the maximum stated pressures and temperatures listed on module's Data Sheet.

Gas Mixture  % Mixture Simulating Gas 45 psig 60 psig 90 psig
O2 / N2  21 / 79  Air 1.77 1.86 1.95
O2 / N2  50 / 50   1.82 1.96 1.99
CO2 / N2 50 / 50   7.81 8.47 9.55
CO2 / N2 15 / 85  Flue gas 5.04 6.04 7.55
CO2 / CH4 50 / 50  Land fill gas 2.79 2.92 3.10

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