Preparation And Properties Of Solvent-resistant Nanofiltration Membrane With PDA/MOF Co-deposited Interlayer

Many industries such as petroleum,chemical,biology and pharmaceutical industries involve the use,separation and purification of a large number of organic solvents.Traditional separation methods（such as distillation,evaporation,rectification and extraction,etc.）not only have high energy consumption,solvent loss,and easy to cause serious environmental pollution.Solvent-resistant nanofiltration technology is an extension of traditional water system nanofiltration technology,which can be used for the separation and purification of organic system solution,and is one of the important green chemical processes to solve energy,resources and environmental problems.Solvent-resistant nanofiltration membrane as the core component,its good separation performance and solvent resistance is the key to the practical application of solvent-resistant nanofiltration technology.In order to obtain good performance of solvent-resistant nanofiltration membrane,solvent-resistant composite nanofiltration membrane was prepared by optimizing ultrafiltration membrane and separation layer respectively.At the same time,an intermediate layer of polydopamine（PDA）and metal-organic framework material（MOF）was constructed between ultrafiltration membrane and the separation layer.The existence of the intermediate layer could not only enhance the interaction between the ultrafiltration membrane and the separation layer,but also improve the solvent resistance of nanofiltration membrane.Moreover,the interfacial polymerization reaction rate in the preparation process of nanofiltration membrane can be controlled macroscopically to obtain high performance solvent-resistant composite nanofiltration membrane.The main research contents and conclusions of this paper are as follows:（1）Preparation of polyetherimide solvent-resistant ultrafiltration base membrane.In order to prepare ultrafiltration membrane with good solvent resistance,polyetherimide（PEI）was used as membrane material to prepare PEI solvent-resistant ultrafiltration membrane by phase inversion method.The effects of PEI concentration and polyvinylpyrrolidone（PVP）concentration in the casting solution on the structure and properties of the PEI solvent-resistant ultrafiltration membrane were investigated,and hexamethylene diamine（HDA）was used for chemical crosslinking after the phase transformation into the membrane.The optimal ratio of the casting solution was obtained as follows:PEI concentration was 18%,PVP concentration was 2.0%,and N,N-dimethylacetamide（DMAc）concentration was 80%.Under the optimal conditions,the pure water flux and the rejection of 1.0 g/L BSA solution of ultrafiltration membrane under the operating pressure of 0.1 MPa are 667L/（m²·h）and 97.6%,respectively.At the same time,the pure water flux can reach 1126.2 L/（m²·h）without reducing the membrane separation performance,and the solvent resistance of the crosslinked ultrafiltration membrane is greatly improved after chemical crosslinking of HDA for 30 min.（2）Preparing solvent-resistant nanofiltration membrane by co-depositing intermediate layer with PDA and MOF.On the basis of the successful preparation of ultrafiltration membrane with good solvent resistance,the solvent-resistant composite nanofiltration membrane was prepared by the typical interfacial polymerization reaction（the water phase monomer was piperazine PIP and the organic phase monomer was trimellitic chloride TMC）after co-deposition of PDA and MOF interlayer.MOF（HKUST-1）material was synthesized at room temperature and pressure.The effects of MOF addition amount,PDA self-polymerization time,PIP concentration,TMC concentration and interfacial polymerization time on membrane structure and properties were investigated.The optimal preparation conditions of nanofiltration membrane were as follows:MOF addition amount 0.6 g/L,self-polymerization time 30 min,PIP concentration 2.25%,TMC concentration 0.40%,interfacial polymerization time 2 min,heat treatment at 70℃10 min.The pure water flux of nanofiltration membranes prepared under these conditions is 56.9 L/（m²·h）at 0.6 MPa operating pressure,and it has high rejection for methyl blue,Bengal rose,Congo red,Coomassie brilliant blue R250,99.4%,92.5%,94.1%and 98.3%,respectively.Compared with the nanofiltration membrane without intermediate layer,the permeation flux of 1.0 g/L Na₂SO₄ and Mg SO₄ solution is about doubled,and it has better hydrophilic property,solvent resistance,tensile property and heat resistance.Only by replacing the filtered pure water,the flux recovery rate reached 78.4%,which has good anti-pollution performance.Long-term running experiments show that the rejection of 0.1 g/L Congo red and methyl blue aqueous solution can be stable at 98.5%and 99.9%.（3）Performance of PA/PDA-MOF/PEI nanofiltration membrane in organic solvent system.The nanofiltration membrane prepared by co-deposition of PDA and MOF were used for the separation and purification of dyes in organic solvent system.It was found that the flux of nanofiltration membrane is very different between water system and organic system,and the requirements for equipment and auxiliary facilities are relatively high in the organic solution system and high-temperature operation process.At the operating temperature of 70℃,the permeation flux and rejection of the PA/PDA-MOF/PEI nanofiltration membrane for 0.1 g/L Congo red/ethanol solution are 3.7 L/（m²·h）and 90.1%,respectively,and it has good high temperature resistance.