Modelling in mixed matrix membranes for gas separation

Various gas permeation models including Maxwell model, Bruggeman model, Lewis-Nielson model and Pal model were compared via a modelling approach with the relative permeance of CO2 against published experimental data on silica filled polysulfone/polyimide (PSF/PI) mixed matrix membranes (MMMs). However, none of the tested models were able to predict the data with good accurately. A closer look at the cross-sectional image by scanning electron microscopy (SEM) indicated that the fillers were actually prolate ellipsoids dispersed within the matrix. Maxwell-Wagner-Sillar model was then employed to investigate the prolate effect and it was observed that the optimization curves of maximum packing (�m) and shape factor (n) showed least deviations. The percentage average absolute relative error (AARE ) value for fitted shape factor (nf) was found to be in the range of 1.12-2.17 at 2-10 bar pressure which showed its robustness. A further evaluation from SEM image showed that the shape factor along z-direction (nz) displayed a minimum deviation of 17.52 for prolates at 0.102±0.01. By using nz as upper limit and estimated shape factor ne through generalization, the error was reduced to 6.01. The AAR deviation was found in the order of nf <ne<nz,which indicated the importance of shape factor parameter for estimating true CO2 permeance. © 2014 Canadian Society for Chemical Engineering.