Modeling Multicomponent Gas Separation Using Hollow-Fiber Membrane Cohtactors

A model developed for multicomponent gas separation using hollow-fiber contactors permits simulation of cocurrent, countercurrent, and crossflow contacting patterns with permeate purging (or sweep). The numerical approach proposed permits simulation to much higher stage cuts than previously published work and provides rapid and stable solutions for cases with many components, with widely varying permeability coefficients. This new approach also permits the rational and straighqorward incorporation of efjects such as permeate sweep, pressure-dependent permeability coeficients, and bore side pressure gradients. Simulation results are presented for separation of commercially significant multicomponent gas mixtures using polymer permeation properties similar to those of polysulfone. The effect of permeate pqing on separation per$ormance is explored for air separation. The influence of pressure ratio on hydrogen separation performance for a refinery stream is presented. Air is modeled as a four-component mixture of 02, N2, C02, and Hz0 and the refinery stream contains five components: Hz, CH4, C2 H4, C2 H6, and C3 Hs. In air separation, permeate purging with a small fraction of the residue stream provides a very eflective method for improving module efficiency for drying but is not eflcient for improving nitrogen purity or recovery. In multicomponent mixtures, maxima in the compositions of components of intermediate permeability may be observed as a function of distance along the hollow fiber. This result suggests the use of membrane staging to capture these components at their maximum concentratbn.