Preparation And Characterization Of Acid-base Blend Solvent Resistant Nanofiltration Membrane

Solvent resistant nanofiltration(SRNF)membranes show very promising prospect in many fields.In recent years,developing a high performance polymer solvent resistance nanofiltration membrane with low cost becomes a hot spot in the field of membrane separation technology.Acid-base cross-linking reaction has been used to improve the performance of acid-base polymer blend membranes,which have been used in fuel cells,full evaporation membranes and ultrafiltration membranes,but less used in the preparation of nanofiltration membranes.Polyetherimide(PEI)possess excellent mechanical stability,thermal stability and chemical stability.Sulfonated polyether ether ketone(SPEEK)owns advantages of mechanical properties,heat resistance,chemical stability,and ion permeability,which is an ideal choice for solvent resistant nanofiltration membrane.In this study,PEI and sulfonated polyether ether ketone sodium salt(Na~+-SPEEK)were selected.The solvent resistant nanofiltration membranes were prepared by acid-base cross-linking,which was then applied to the solvent resistant nanofiltration process.The relationship between membrane morphology and their performance was clarified by studying their forming process,cross-linking mechanism and microstructure.The main work is as follows:(1)The acid-base blend nanofiltration membranes were prepared via immersion precipitation phase inversion method.The mass concentration of polymer PEI in the casting solution is 20 wt%.The structure of membranes was tuned by varying the ratio of Na~+-SPEEK to PEI in the casting solution(0.8/10,1/10,1.34/10,2/10,4/10)to obtain the acid-base blend nanofiltration mambranes with different morphology.With the increasing of the ratio,the thickness of the membrane skin layer increased firstly and then decreased.The retention of dye increased firstly and then decreased,and the solvent flux decreased firstly and then increased.The membrane(ratio is 1.34/10)possess best performance.(2)To further enhance the performance of nanofiltration membrane,the membranes were modified by acid-base cross-linking reaction.The mass concentration of PEI is 20 wt%,the ratios of Na~+-SPEEK to PEI are 1/10,1.34/10,and 2/10.The properties of nanofiltration membranes before and after cross-linking were investigated.Compared with the original membrane,the rejection of dye increased significantly,and the flux declined.The cross-linked membranes(ratio is 1.34/10)possess best performance.For example,the rejections of Rose Bengal in isopropanol,ethanol and acetone were above 98%.The rejection improved from32.19%to 99.67%on Rose Bengal in acetone after cross-linking.The cross-linked nanofiltration membranes exhibited good separation performance.(3)To investigate the effect of film formation conditions(the concentration of polymer in the casting solution)on the properties of nanofiltration membrane.The ratio of Na~+-SPEEK to PEI was fixed to 1.34/10,the morphology of the acid-base blend nanofiltration membrane was tuned via changing the concentration of PEI(17 wt%,20 wt%,23 wt%).The nanofiltration membrane was modified to study the morphology of the membrane,the stability in the solvent,and the change in separation performance.With the increasing the concentration of PEI,t`he skin layer became thicker and more dense,the rejection increased obviously,and the flux decreased.Compared with the original nanofiltration membranes,after cross-linking,the performance and the membrane stability improved obviously.For example,in the membranes(23 wt%),the rejection increased from 44.21%to 98.33%on Rose Bengal in acetone solution after cross-linking.The membranes showed excellent stability in DMF after cross-linking(the original membranes dissolved in DMF),the rejection of Rose Bengal in DMF was 90.90%.