Study on chitosan-polyvinyl alcohol blends/poly (acrylonitrile)(PAN) composite nanofiltration membrane

A positively charged composite nanofiltration(NF) membrane is prepared by coating solution of chitosan and polyvinyl alcohol blends on a PAN ultrafiltration(UF) membrane,subsequently crosslinking with glutaraldehyde(GA).The effects of membrane preparation conditions such as crosslinking time and temperature,GA concentration,etc on membrane properties are studied.The optimal condition is obtained by single-factor experiment as follows: 1.5wt% chitosan and polyvinyl alcohol,cured at 50℃ for 2h,crosslinking at 40℃ for 4h with GA/ethanol=0.75∶50(w/w),heated for 15min at 50℃ finally.At 25℃ and 30L/h of cycling flow and 1.0MPa of operating pressure,the effects of the operation conditions such as operating pressure and type of feed,etc on membrane performance are also investigated.Its pure water permeability is 5.80L/(h·m2·MPa).The retention rate to 1000mg/L NaCl,MgCl2,MgSO4 and Na2SO4 solutions are 63.50%,94.30%,81.00% and 32.70%,respectively,with the flux of 3.10,3.65,2.40 and 2.70L/h·m2,respectively.The retention rate for different salt solutions follows the deceasing order of MgCl2,MgSO4,NaCl,Na2SO4,revealing the characteristic of positively charged NF membrane.Besides,the curve about the streaming potential illuminates the positively charged characteristic of this membrane further,with a pressure osmotic coefficient of 5.68mV/MPa.The structure characteristic of the NF membrane is characterized by scanning election microscope revealing the composite structure of the NF membrane.