Study On Preparation And Separation Properties Of Anti-fouling And Chlorine-resistant Polyamide Membrane

Reverse osmosis membrane and its separation technology play a leading role in advanced treatment of industrial wastewater,and therefore is considered to be a reliable and effective method to reduce industrial water pollution.However,the use of conventional polyamide(PA)reverse osmosis membrane for industrial wastewater treatment is limited by some scientific problems,including limited hydrophilicity of its surface,its ease to be contaminated and degraded by chlorination,mutual restriction of salt rejection and water flux,unclear separation mechanism,etc.In this study,a series of aromatic polyamide reverse osmosis composite membranes with high performance were prepared based on interfacial polymerization,radical polymerization,etc.,and used for advanced treatment and efficient separation of industrial wastewater by synergistic effects of several mechanisms,including separation mechanism,chlorine resistance mechanism,anti-fouling mechanism,etc.It is expected that this study will provide a valuable reference for design and preparation of high-performance aromatic polyamide reverse osmosis composite membranes.Based on "Graft to" irradiation grafting method,polyvinylpyrrolidone(PVP)was grafted on the surface of aromatic polyamide composite membrane to prepare the hydrophilic PA-g-PVP reverse osmosis composite membrane.The influential factors,including irradiation conditions,grafting agent concentration and molecular weight,irradiation gas atmosphere,etc.,were discussed in detail.PVP grafting can improve the hydrophilicity and electronegativity of the membrane surface,and synergically enhance steric hindrance and electrostatic repulsion.The chemical composition and surface morphology of the grafted polyamide membranes were significantly changed.The hydrophilicity and anti-fouling properties of the reverse osmosis membrane can be significantly improved by PVP molecular brushes grafted onto its surface.The prepared PA-g-PVP reverse osmosis composite membranes have a static water contact angle of 24.3°,anti-fouling rate of 93.4%,and inorganic salt rejection of 99.3% within the acceptable range of permeable water flow.Water-soluble N-vinyl-2-pyrrolidone(NVP)was infiltrated to low cross-linked polyamide membrane as seed agent by bionic construction,interfacial polymerization and radical polymerization to prepare hydrophilic anti-fouling PA-g/co-NVP reverse osmosis composite membrane.Water-soluble olefin monomer NVP downwards infiltrated the PA layer and formed a highly stable PA-g/co-NVP structure under irradiation,thus synergically controlling the surface and main microstructure of the membrane.The PA-g/co-NVP reverse osmosis composite membrane prepared after addition of 1.0% NVP has the bovine serum albumin(BSA),sodium alginate(SA)and sodium dodecyl sulfate(SDS)flux recovery rates(FRR)of 91.23%,96.28% and 93.67%,respectively.The hydrophilic angle of the membrane surface was reduced to 18.8°,and the hydrophilicity of the composite membrane surface was greatly improved.The prepared PA-g/co-NVP reverse osmosis composite membrane has excellent separation stability,limits matrix expansion and interfacial delamination,and shows good separation performance and anti-fouling property in pharmaceutical wastewater treatment.PA-g/co-DADAMC reverse osmosis composite membrane,which was designed and prepared from interfacial polymerization and in-situ radical polymerization and coupling of diallyl dimethyl ammonium chloride(DADMAC)and water-soluble monomer,has nano-scale water channels and hydrophilic molecular separation layers similar to interpenetrating networks.DADAMAC used for radical polymerization is dispersed inside and on PA functional layer to form a functional layer with polyolefin interpenetrating network structure and a hydrophilic surface layer with hydrophilic molecular brush,respectively.At the same time,DADMAC was introduced to convert amide bonds on the molecular chains of polyamide to amide bonds(i.e.N-H converted to N-C),which effectively improved the chlorination tolerance of polyamide membrane materials.PA-g/co-DADAMC reverse osmosis composite membranes have a water contact angle of 19.95°,much lower water contact angle,lower surface roughness and fewer negative charges than traditional thin film composites(TFC).PA-g/co-DADAMC reverse osmosis composite membrane materials have 11.36% higher permeation flux,higher salt rejection(99.31%),and higher low molecular weight organic matter removal(COD > 99.3%)in separation test of textile wastewater than the reference TFC RO membrane,the removal ability of was higher.In addition,the PA-g/co-DADAMC membrane has good antimicrobial activity and satisfactory stability in long-term separation.