Fabrication of porous polysulfone microsphere covalently grafted with ionic liquid as catalyst and its catalytic hydrolysis kinetics of inulin

Polysulfone (PSF) material loaded with ionic liquids (ILs), PSF-ILs, was prepared by grafting imidazolyl acid ILs onto PSF by chemical bonding. A porous PSF-ILs microsphere catalyst was prepared via non-solvent induced phase separation (NIPS) method in order to catalyze the biomass inulin hydrolysis. The influences of degree of chloromethylation of PSF, hydrolysis temperature, catalyst dosage, PSF-ILs microsphere morphology, coagulation bath of NIPS and inulin concentration on hydrolysis performance were studied respectively. Under this optimal reaction conditions, 95.65% conversion of inulin into reducing sugar was achieved. The results suggested that the catalytic inulin hydrolysis performance of PSF-ILs microsphere was attractive due to high-density spatial distribution of the active sites on the surface and inner pore wall of microsphere after ILs immobilized. The hydrolysis kinetics was also investigated. The kinetic models of inulin hydrolysis catalyzed by PSF-ILs microsphere were employed to predict the hydrolysis in a wider range of experimental conditions. Furthermore, the stability tests showed that PSF-ILs microsphere catalyst could be effectively separated and recovered from hydrolysates, and has good regeneration ability. The morphology of PSF-ILs microspheres remained intact after eight trials of catalytic hydrolysis, avoiding the crushing phenomenon like a powder polymer material. More importantly, the PSF-ILs microsphere can effectively avoid the potential harm of ILs to the ecological environment, and is a potential green catalyst.