Mindel S-1000 Based Asymmetric Membranes for O₂/N₂ Separation: Effect of Polymer Concentration

Abstract

Commercially blend of polysulfone (PSf) and acrylonitrile-butadiene-styrene (ABS) resin known as Mindel S-1000 was used to prepare flat sheet membranes for O2/N2 separation. The produced membranes were expected to inherit the excellent gas separation properties of polysulfone and strong mechanical properties of ABS. Asymmetric membranes were successfully prepared by a pneumatically-controlled casting machine with methanol as the second coagulation medium. Commonly use solvents for pure PSf and ABS; N-methyl-2-pyrrolidone (NMP) and a more volatile tetrahydrofuran (THF); were chosen in the dope formulation. The polymer concentration was varied between 20 to 23.5% to promote the formation of the desirable membrane morphology that affecting the gas separation performance. As the concentration increased, a more oriented membrane with denser skin layer was developed that was responsible for the slight improvement in gas separation factors with slight reduction in gases permeabilities. However, as the solution became too viscous due to the high content of polymer, solvent evaporation was hindered during the solvent-exchange process producing membranes with huge microvoids and thinner skin. To further promote the membrane skin formation, solvent ratio of the dope solution was manipulated. Membrane morphology analysis revealed that the increment of solvent ratio; reducing the volatile solvent, promoted the membrane porosity while decreasing the skin thickness. Thus, a significant loss of gas pair selectivity was observed as the permeability increased. In order to enhance the membrane performance and plugged any possible defects on the skin surface, the produced membranes were silicone coated. This step improved the membrane gas separation performance while retaining the same trend as the uncoated membranes. Due to the dispersion of rubber particles in ABS that contributed to the toughness of the polymer, the mechanical properties of PSf-ABS membranes were found to be high with comparable elasticity to other common polymeric membranes.