Preparation Of Poly(Aryl Ether Sulfone) Solvent Resistant Nanofiltration Membranes

Over the past decade, nanofiltration has gained a lot of attention, as it is a simple and energy-efficient unit process to separate mixtures down to a molecular level. At present, most nanofiltration membranes are mainly used in aqueous solution system. However, few solvent resistant nanofiltration(SRNF) membranes can be used in the fields such as petroleum and chemical catalytic non-aqueous solution system. The materials of commercial SRNF membranes are mostly prepared with polyimide and silicone rubber, but they are expensive and poor solvent risistance, so it is significance to develop new SRNF membranes.Polysulfone (PSf), poly(ether sulfone)(PES) and poly(phthalazinone ether sulfone)(PPES) have excellent comprehensive performance, widely used in the preparation of ultrafiltration membrane and the support layer of composite membrane. Because of theirs poor solvent resistance of the material itself, they are seldom used in the preparation of SRNF membrane directly. In order to enable them to apply in the solvent system, crosslinking modification is generally needed to improve theirs solvent resistance. Chloromethyl polysulfone (CMPSf), chloromethyl polyether sulfone (CMPES) and chloromethyl poly(phthalazinone ether sulfone)(CMPPES) are prepared from PSf, PES and PPES respectively. The chloromethyl content of CMPSf, CMPES and CMPPES are in a range of1.50-2.50mmol/g. Base membranes are prepared from CMPSf, CMPES and CMPPES through method of phase inversion, and then aminaed to prepare SRNF membranes.The effects of composition of casting solution (the type and concentration of polymer, additives) and the technology of membrane preparation (solvent evaporation time, heating temperature, coagulation bath temperature) on the membrane’s structure and performance are investigated in the preparation process of base membrane. The results show that the selectivity of nanofiltration membranes increase and flux decline with increasing polymer concentration, butanone concentration, solvent evaporation time and heating temperature. However, the selectivity decline and the flux greatly increase with increasing coagulation bath temperature and LiCl concentration. The membranes prepared with CMPPES exhibit a permeate flux of75.4L/m2h and45%retention of0.1g/LMgCl2, a permeate flux of24.5L/m2h and90%retention of0.1g/LMB. The flux and retention of CMPPES membrane for the two test solution are higher than those of membranes prepared from CMPSf and CMPES. The effects of content of chloromethyl and amination agent on the separation performance of membrane and solvent resistance are investigated. With increasing content of chloromethylation, the selectivity of nano filtration membranes increase and the flux decline. The crosslink density enhances because of the increasing of content of chloromethyl, so the solvent resistance of membrane improves. Three kinds of base membranes are respectively immersed in25v.%ethylenediamine aqueous solution,25v.%hexamethylenediamine aqueous solution, mixed solution of15v.%ethylenediamine and10v.%trimethylamine, mixed solution of15v.%hexamethylenediamine and10v.%trimethylamine to prepare SRNF membranes, the separation performance and solvent resistance are tested. The results show that the selectivity of membranes prepared by mixed amination agent on0.1g/L MgCb solution is higher than or close to that of membranes prepared by pure diamine, and the flux has a significant improvement The membranes prepared by mixed amination agent on0.001wt.%of the methylene blue ethanol solution show lower selectivity and higher flux than the membranes prepared by pure diamine. Solvent resistant tests show that the stability of nano filtration membranes prepared by pure diamine is slightly higher than that of membranes prepared by mixed amination.