Geometric restriction of microporous supports on gas permeance efficiency of thin film composite membranes

Abstract

Gas permeance of thin film composite (TFC) membranes may be restricted by the porosity and pore size of microporous supports, resulting in a reduction in permeance. This work extends a theoretical expression presented in the literature to describe the geometric restriction of the microporous supports on gas permeance efficiency in the TFC membranes. For this purpose, the permeance efficiency of penetrants through forty-eight different TFC membranes is systematically investigated. The experimental results are modelled using two equations developed by Wijmans and Hao, and Ramon, Wong and Hoek. The overall relative error for the values predicted by the Wijmans-Hao and Ramon-Wong-Hoek equations are 31% and 38%, respectively. The Wijmans-Hao equation was developed based on computational fluid dynamics (CFD) studies. We demonstrate that a modification of the Wijmans-Hao equation by introducing the number of pores per unit surface area of the microporous support layer, Np, in the definition of the scaled thickness (S=lrp, where l and rp are respectively selective layer thickness and mean pore size of support layer) improves its estimation precision. Therefore, the definition of scaled thickness is modified to the following equation:Sm=lrp/σwithσ=a(πNp)bwhere a and b are adjustable parameters. The deviation of the modified Wijmans-Hao equation from the experimental values reduces to 9.4%.