Structure Control Of Polysulfone Support Membranes And Preparation Of Composite Reverse Osmosis Membranes

The performance of the composite reverse osmosis membrane not only depends on the selective separation layer,but also is affected by the structure and morphology of the porous support membrane.A suitable porous support membrane is the basis for preparing a high-performance composite reverse osmosis membrane.In this paper,a series of flat membranes were prepared by immersion precipitation method using polysulfone(PSF)as the membrane material,N,N-dimethylacetamide(DMAc)as the solvent,?-butyrolactone(GBL)as the second solvent,isopropyl alcohol(IPA)as the non-solvent additive,and water as the coagulation agent.The effects of DMAc/GBL mass ratio,approaching ratio?,and PSF mass concentration on the membrane structure and performance were discussed herein.Then,the polyamide/polysulfone composite reverse osmosis membrane was prepared by the classic interfacial polymerization method,and the influence of the polysulfone support membrane on the separation performance of the composite reverse osmosis membrane was investigated.The research results were as follows:Firstly,we had study on the structure control of polysulfone support membrane.As the mass ratio of DMAc/GBL in the casting solution decreased,the viscosity of the casting solution increased,the support membrane changed from finger-like structure to sponge-like structure,the support membrane surface pore size decreased,and the pore size distribution became narrow.The increase of GBL content effectively inhibited the formation of large pores and the reduced molecular weight cut-off.As the value ofαincreased from 0 to 0.9,the viscosity of the casting solution increased,the solvent exchange rate slowed down,the formation of finger-like pores was suppressed,and the pore size distribution of the prepared support membrane became wider,and the retention performance decreased.At the same time,the flux of pure water greatly increased,and the hydrophilicity of the membrane increased.As the PSF mass concentration increased,the formation of sponge-like pores was promoted,the skin and sublayer of the support membrane became denser,and the molecular weight cut-off and flux were decreased significantly.The support membrane prepared with PSF mass concentration of 20%,DMAc/GBL mass ratio of 1:1 and approaching ratio value of 0.5 had the best separation performance.It had a molecular weight cut-off of 50 KDa,a pure water flux of 128 L/(m~2·h·bar),an average surface pore diameter of 8.9 nm,a geometric standard deviation of pore size of 1.305,and a narrow pore size distribution.Secondly,using m-phenylenediamine(MPD)and trimesoyl chloride(TMC)as monomers,polyamide/polysulfone composite reverse osmosis membranes were prepared by interfacial polymerization.Through the characterization of the separation performance of reverse osmosis membranes,it was found that the composite membranes prepared using PSF support membranes with small average surface pore size and narrow pore size distribution had higher salt rejection.The composite reverse osmosis membrane prepared using PSF support membrane with a large average pore size had higher flux.Preparation of composite reverse osmosis membrane used PSF support membrane with average pore diameter of 8.9nm.Its salt rejection reached 97.18%,and the flux was 20.5 L/(m~2·h).Finally,the effect of operating temperature on the separation performance of the polyamide/polysulfone composite reverse osmosis membrane was investigated.The results showed that as the operating temperature increased from 30 ~oC to 80 ~oC,the flux of the reverse osmosis membrane increased by two times,while the salt rejection decreased slightly.