Gas permeation and selectivity characteristics of sponge-like and finger-like structures of polysulfone membranes

The structure of polysulfone (PSF) membranes, whether finger-like pores (FP) or sponge-like pores (SP) structures, plays a major role in the mechanisms of gas separation and the efficiency of their process. In this study, the impact of finger-like (FP) and sponge-like (SP) structures on the gas permeability and selectivity of PSF membranes were examined. The PSF membranes were prepared using a phase inversion method at different thicknesses of 100 µm and 200 µm for SP and FP structures respectively. The characteristics of both membranes such as pore structure, morphology, porosity, functional groups, crystallinity, thermal stability, and mechanical behaviour were measured. While the CO2, N2, H2, CH4 gas permeation were measured up to 60 ˚C and at various pressures. The FP/PSF membrane had smaller pore size (61 nm), higher porosity (81%), better mechanical strength (3 MPa), higher thermal stability (46%), higher working pressure (3 bar), and crystallinity than to the SP/PSF membrane. In addition, the FP/PSF membrane had higher permeability for H2 (722037 Barrer) > CH4 (348422 Barrer) > CO2 (252060 Barrer) > N2 (225374 Barrer) with a significant increase of 1291% (H2), 1448% (CH4), 1247% (CO2), and 1711% (N2) compared to the SP/PSF membrane. Furthermore, FP/PSF membrane exhibited better selectivity for H2/CH4 (3.2), H2/N2 (3.7), H2/CO2 (7.3) with 39–51% improvement compared to SP/PSF membrane. Based on these results, membranes with finger-like structure are highly recommended for use in gas separation applications.