Preparation And Properties Of EVOH Nanofiber-based Nanofiltration Membrane With Twill Structure

Membrane separation technology has been widely used in seawater desalination,wastewater treatment and other fields.Membrane fouling is a common phenomenon in the application process of membrane separation,which can lead to flux decrease,membrane structure damage and even failure,and has become a key problem restricting the application and development of membrane separation technology.Therefore,nanofiltration membranes with excellent filtration and separation performance,fouling resistance and stability have always been the main direction of nanofiltration membrane research in response to membrane pollution.In order to design nanofiltration membranes with high flux,high rejection rate,excellent anti-fouling performance and in line with different separation standards,a nylon microfiltration membrane with a twill structure is selected as the support layer of the nanofiltration membrane,and the interfacial polymerization method is used to prepare the membrane.The PIP/TMC-nylon negatively charged polyamide nanofiltration membrane and PEI/TMC-nylon positively charged polyamide nanofiltration membrane are investigated,and the filtration and separation performance,antifouling performance and stability of the membranes are comprehensively evaluated.The research results obtained are as follows:(1)NFM-nylon microporous support membrane with nanofiber gram weight of 6 g/m2 is prepared by selecting 400 mesh nylon mesh as the substrate.The results showed that the average pore size of NFM-nylon and NFM-PET are 162.6 nm and 192.1 nm and the dye rejections are 99.84% and 97.04%,respectively.The results of anti-pollution test show that the flux recovery rates of NFM-nylon and NFM-PET are 74.99% and 0.38%,respectively.NFM-nylon with twill texture structure not only has higher flux stability and dye rejection,but also has excellent antifouling performance compared with NFM-PET.The main reason is that NFM-nylon has a concave and convex twill structure.On the one hand,this structure can increase the effective filtration area,thereby increasing the water flux;On the other hand,the twill undulating structure can produce turbulence,which is easy to reduce the adhesion of pollutants on the membrane surface,thus improving the surface fouling resistance.Meanwhile,the average pore size of NFM-nylon is smaller than that of NFM-PET,so the retention performance of dyes is better.(2)PIP/TMC-nylon negatively charged polyamide nanofiltration membrane with twill structure is prepared by interfacial polymerization with NFM-nylon as support layer and PIP and TMC as reactive monomers.The results show that the pure water flux of PIP/TMC-nylon is 438.75 L/(m2 h MPa),the permeation flux of Na2SO4 solution is 317.29 L/(m2 h MPa),and the retention rate is 97.47%;The pure water flux of PIP/TMC-PET is 332.5 L/(m2h MPa),the permeation flux to Na2SO4 solution is 212.92 L/(m2 h MPa),and the rejection rate is 95.49%.Antifouling tests show that the flux recovery rates of PIP/TMC-nylon and PIP/TMC-PET are 88.42% and 43.33%,respectively.Compared with PIP/TMC-PET,PIP/TMC-nylon not only has higher permeation flux and retention rate,but also has stronger antifouling ability.The main reason is that PIP/TMC-nylon has a twill structure,which can increase the surface roughness of the membrane,increase the permeation area of the selected layer,and improve the permeability of the nanofiltration membrane;On the other hand,twill undulating structure is easy to produce turbulence,reduce resistance,can better inhibit membrane pollution,so as to improve the fouling resistance of nanofiltration membrane.Meanwhile,due to the better hydrophilicity of the base membrane of PIP/TMC-nylon,the PIP is easier to transport,which promotes the interfacial polymerization and makes the PA layer denser,thereby improving the retention rate of PIP/TMC-nylon.(3)PEI/TMC-nylon positively charged polyamide nanofiltration membrane with twill structure is prepared by interfacial polymerization with NFM-nylon as support layer and PEI and TMC as reactive monomers.The results showed that the pure water flux of PEI/TMC-nylon is 250.63 L/(m2h MPa),the retention flux of Mg Cl2 solution is 187.08 L/(m2 h MPa),and the retention rate is 93.56%;The pure water flux of PEI/TMC-PET is 176.04L/(m2h MPa),the retention flux of Mg Cl2 solution is 144.79 L/(m2h MPa),and the retention rate is 87.2%.Antifouling tests showed that the flux recovery rates of PEI/TMC-nylon and PEI/TMC-PET are 73.24% and 39.34%,respectively.Compared with PEI/TMC-PET,PEI/TMC-nylon not only has high permeability and high rejection,but also has strong antifouling ability.The main reason is that PEI/TMC-nylon has a concave and convex twill structure,which increases the permeation area of ? ? the selective layer and improves the permeability of the nanofiltration membrane;On the other hand,the twill undulating structure can produce turbulence,which is easy to reduce the adhesion of pollutants on the membrane surface and optimize the fouling resistance of nanofiltration membrane.Meanwhile,due to the better hydrophilicity of the base membrane of PEI/TMC-nylon,the PEI is easier to transport,which promotes the interfacial polymerization and makes the PA layer denser,thereby improving the retention rate of PEI/TMC-nylon.