A study of the effects of mixtures of solvents on CO2/N2 gas separation in polysulfone flat sheet membranes

Abstract

Different solvents were used to produce polysulfone (PSF) membranes. These solvents included, Tetrahydrofuran(THF), N,N-dimethylacetamide(DMAc), Dichloromethane(DCM) and N-methyl-2-pyrrolidone (NMP). Gas permeability was greatest for the PSF membrane prepared with NMP, while selectivity was best for the THF membrane. Tetrahydrofuran (THF) was added into the casting solution at varying loadings (from 0% to 35%) to create asymmetric membranes with excellent gas separation performance. In SEM, the layer of the membrane that was prepared with NMP as the solvent is the thickest, while the layer of the membrane that was made with NMP/THF as solvent mixture is the thinnest. In gas permeability tests, as the amount of THF increases with NMP, it has the highest CO2/N2 selectivity and the lowest permeability. PSF/NMP has the highest permeabilities for CO2 (0.0728 GPU) and N2(0.0186 GPU), and the lowest selectivity for CO2/N2. Because of the thinner skin layer, CO2 and N2 are able to pass through more easily, while the low selectivity is the result of a surface defect in the form of a pin-hole. The maximum CO2/N2 selectivity is 8.69 for PSF/NMP/THF.