Fabrication of porous polymer membrane from polysulfone grafted with acid ionic liquid and the catalytic property for inulin hydrolysis

Catalytically active membranes are the core components of the membrane reactors. Polysulfone (PSF) grafted with ionic liquids (ILs), PSF-DG-ILs, was prepared via introducing chloromethyl group into benzene ring of PSF, then grafting ILs, imidazolyl acid ILs ([(CH₂)₃SO₃HVIm]HSO₄), by chemical bonding. Then PSF-DG-ILs membranes were prepared by non-solvent induced phase separation technique for hydrolysis of inulin. The effects of coagulation bath, grafting degree, and various dope blending on structure, physico-chemical characters, and catalytic performance of membranes were evaluated. And results revealed that catalytic performance could be efficiently enhanced by choosing ethanol as coagulation compared with ethyl acetate, which was mainly attributed to surface segregation. Membrane mechanical strength decreased with the enhancing ILs grafting degree, while the catalytic performance increased. However, PSF-DG-ILs with high degree of ILs grafting lost its membrane-forming property. The mechanical and catalytic properties of the membrane were synergistically enhanced by blending PSF-DG-ILs polymers with high and low ILs grafting degree, then the resulting membranes broke the trade-off effect between mechanical strength and catalytic ability. Specifically, membrane fabricated by mixing the polymers with ILs grafting degree of 0.31 and 0.59 integrates optimized mechanical property and catalysis performance. The strength and strain of this blending membrane are 3.17 MPa and 14.10%. The average pore size and porosity are 215.5 nm and 46.2%. The yield of inulin hydrolysis can reach 88.22% with 20 wt% concentration of inulin at 75 °C using a flux of 23.4 L/(m²·h). Therefore, the PSF-DG-ILs membrane displayed promising potential for the application in biomass conversion.