Gas separation by permeation Part I. Calculation methods and parametric analysis

Calculation methods for single- and multi-stage permeation of a multi-component mixture are presented. The use of the local permeate concentration in the formulation results in a relatively simple form of solution for the binary system in the cross-flow pattern. A parametric analysis of the permeation cascade is given. For a given permeability of the more permeable component, there exists a membrane selectivity which gives rise to a minimum membrane area requirement in the cascade. It is shown that the compression power requirement is dependent only on the operating pressure ratios, irrespective of actual pressure levels in each stage. A study on the effect of interstage mixing loss shows that the ideal cascade (with no interstage mixing loss) is not necessarily always the thermodynamically most efficient one; some non-ideal cascades may have higher efficiencies due to more effective permeation steps. Examples given relate to He/CH4 and O2/N2 separations.