MODELING MULTICOMPONENT GAS SEPARATION USING HOLLOW-FIBER MEMBRANE CONTACTORS

A model developed for multicomponent gas separation using hollow-fiber contactors permits simulation of cocurrent, countercurrent, and cross flow contacting patterns with permeate purging (or sweep). The numeric al 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 coeffici ents. This new approach also permits the rational and straight forward incorporation of effects such as permeate sweep, pressure-dependent p ermeability coefficients, and bore side pressure gradients. Simulation results are presented for separation of commercially significant mult icomponent gas mixtures using polymer permeation properties similar to those of polysulfone. The effect of permeate purging on separation pe rformance is explored for air separation. The influence of pressure ra tio on hydrogen separation performance for a refinery stream is presen ted Air is modeled as a four-component mixture of O-2, N-2, CO2, and H 2O and the refinery stream contains five components: H-2, CH4, C2H4, C 2H6, and C3H8. In air separation, permeate purging with a small fracti on of the residue stream provides a very effective method for improvin g module efficiency for drying but is not efficient for improving nitr ogen purity or recovery. In multicomponent mixtures, maxima in the com positions of components of intermediate permeability may be observed a s a function of distance along the hollow fiber. This result suggests the use of membrane staging to capture these components at their maxim um concentration.