Preparation And Properties Of Polypiperazinamide Composite Nanofiltration Membranes By Positive And Negative Interface Methods

Nanofiltration(NF)can effectively reject molecular weight cut-off(MWCO)ranging from 200 to 1000 and multivalent ions,and NF with advantages of low energy consumption,high rejection and low operating pressure has been widely applied in seawater desalination,drinking water softening,food industry and other fields.At present,most commercial NF membranes are composite NF membranes,and polyamide separation layer is prepared by interfacial polymerization on the surface of porous membrane.In this work,polyamide composite NF membrane was prepared by interfacial polymerization(IP-F),and the effects of interfacial polymerization time,piperazine(PIP)concentration and post-treatment temperature on the performance of composite NF membrane were studied.Under the operating pressure of 0.5 MPa,the common salt solution,heavy metal salt solution and dye were tested to comprehensively evaluate the separation performance of the composite NF membrane.At the same time,the polyamide coating was prepared by inverse interfacial polymerization(IP-R),and polyacrylic acid(PAA)with negative charge was introduced on the surface of polyamide to prepare composite NF membrane with negative charge.The effects of PAA deposition time,PAA concentration and pip concentration on the performance of composite NF membrane were studied.The surface morphology and composition of the composite NF membrane were carried out by FESEM and FTIR.The main contents and results of this work are as follows:(1)The effect of polyvinylpyrrolidone(PVP)concentration on the permeation flux of polysulfone(PSF)membrane was studied.The results show that when the concentration of PVP is 0.25 wt%,the permeability of the modified membrane is better.Polyamide composite NF membrane was prepared by interfacial polymerization(IP-F)on the surface of the modified PSF membrane.The effects of preparation conditions on the performance of composite NF membrane were investigated.The results show that the best preparation conditions:the interfacial polymerization time is 30 s,PIP concentration is 0.25 wt%and post-treatment temperature is 60?.The order of rejection of composite NF membrane for different salt solutions is as follows:MgSO₄>Na₂SO₄>CuSO₄>NiSO₄>NaCl.The rejection of Eosin Y(EY)and methyl green(MG)are almost 100%.(2)Polyamide NF membrane was prepared by inverse interfacial polymerization(IP-R),and PAA with negative charge was introduced into polyamide coating.The results show that the best preparation conditions:the deposition time of PAA is 10 min,the concentration of PAA is 0.18 wt%and the concentration of PIP is 0.5 wt%.The order of rejection of composite NF membrane for different salt solutions is as follows:Na₂SO₄>MgSO₄>CuSO₄>NiSO₄>NaCl.The rejection of Eosin Y(EY)and methyl green(MG)are 84.7%and 79.6%,respectively.