Preparation And Properties Of High Performance Poly(aryl Ether Nitrile) Liquid Separation Membranes

As the global population grows and industrial society develops,the discharge of domesticsewage and industrial wastewater has gravely endangered the health of water resources,exacerbating the water shortage crisis and hurting the healthy development of human society.Therefore,the separation and purification technology for sewage/wastewater treatment has sparked widespread concern.In comparison to classic separation processes such as distillation,extraction,and crystallization,membrane separation technology clearly offers advantages of high separation accuracy,low energy consumption,and nvironmental friendliness.As a research hotspot of membrane separation technology,polymer liquid separation membrane often faces the problems such as low select-permeability,and membrane fouling in practical separation applications.The morphology and surface properties of polymeric membrane play a decisive role in its separation performance.In this paper,bisphenol A poly(aryl ether nitrile)PEN(BPA)was first used as the polymeric membrane matrix material to systematically study the composition of the casting solution corresponding to the preparation of PEN(BPA)ultrafiltration(UF)membrane with high separation performance.Then,the antifouling properties of PEN UF membrane was enhanced by physical blending and bulk modification.Finally,carboxylated poly(aryl ether nitrile)(PEN-COOH)tigh UF membrane with excellent dye/salt mixture separation performance was prepared by using the strong electronegativity of the material,which have promising applications in dye wastewater separation.The main work was as follows:1.Using PEN(BPA)as the polymeric membrane matrix material,this chapter systematically investigates the effects of the composition conditions of the casting solution,such as solvent selection,polymer concentration,additive type and content,on the morphological structure and separation performance of PEN UF membrane.It will provide theoretical guidance for realizing the controllable preparation of PEN porous membrane.Through the above systematic studies:firstly,the PEN membranes prepared by polymer/solvent system had poor permeability and no significant separation performance.Secondly,the increase of polymer concentration increased the denseness of the corresponding prepared PEN membranes,and there was an trade-off effect between pure water(permeate)flux and BSA rejection rate.Furthermore,both the addition of hydrophilic PEG and PVP could effectively improve the permeability of PEN membranes.The pure water(permeate)flux of PEN/PEG membrane rose dramatically as the PEG molecular weight increased,while the overall BSA rejection rate was abover 98%.However,the permeability of PEN/PVP membrane fluctuated as PVP molecular weight increased.Finally,the permeability of PEN/PEG10000membranes fluctuated as PEG10000 content increased,but had no significant effect on BSA rejection rate.The above studies showed that the successful preparation of PEN UF membranes with excellent separation performance was achieved by optimizing the composition of the casting solution.Its pure water and permeate fluxes were 524.6 and 184.5 L·m^-2·h^-1,respectively,meanwhile BSA rejection rate was 99.2%.However,PEN membranes are susceptible to membrane fouling resulting in the degradation of membrane performance.2.In order to enhance the anti-fouling properties of PEN membrane,this chapter adopts the physical blending method to dope zwitterionic silica(Si O₂)nanoparticles into the PEN membrane matrix,so as to prepare PEN nanocomposite membrane with enhanced permeability and anti-fouling performance.And the effect of nanoparticle doping amount on the separation performance of PEN nanocomposite membrane was also investigated.Firstly,the doped zwitterionic Si O₂ nanoparticle was prepared by grafting zwitterionic material lysine onto the surface of the filler particles using the amphiphilicity of KH560.Modification effects include:weakening interparticle agglomeration,improving organic-inorganic phase compatibility,and enhancing particle hydrophilicity.During the membrane formation process,the hydrophilic nanoparticles will gradually migrate and enrich to the polymeric membrane surface along the direction of solvent external diffusion to improve the hydrophilicity of PEN nanocomposite membrane.Specifically,the pure water and permeate fluxes of PEN-0.5 membrane prepared with zwitterionic Si O₂ doping amount of 0.5wt%was 507.2 and 247.1 L·m^-2·h^-1,respectively.And the corresponding BSA rejection rate was 97.4%.Meanwhile,the BSA static adsorption capacity of PEN-0.5 membrane was reduced to 72.9?g·cm^-2,and the FRR was up to 85.3%,indicating the significant improvement of the anti-fouling performance of the PEN-0.5 membrane.However,in the long-term separation process of organic-inorganic composite membranes,inorganic fillers are easily eluted from the membrane matrix due to the weak interaction between the two phases,resulting in a decrease in membrane performance.3.In order to prepare PEN UF membranes with durable anti-fouling properties,this chapter introduced phenolphthalein(PPL)component into the PEN molecular chain skeleton by means of the bulk modification.The prepared phenolphthalein-type poly(aryl ether nitrile)opolymers(PEN-COOHs)with stronger hydrophilicity were synthesized to produce PEN-COOHs UF membranes.The experimental results showed that the higher the PPL component feeding ratio,the lower the molecular weight of the prepared PEN-COOHs,and the enhanced thermodynamic stability of the corresponding casting solution.The surface denseness of the prepared PEN-COOHs membranes increased and the porosity decreased,the pure water(permeate)flux and hydration permeability coefficient gradually decreased,and BSA rejection rate slightly increased.The BSA static adsorption capacity decreased,and the related anti-fouling performance parameters:Rt decreased,FRR increased,which can indicate the enhanced anti-fouling performance of PEN-COOHs membranes.PEN-COOH-60%membrane with the optimum membrane properties had a PWF of 351.7 L·m^-2·h^-1,permeate flux of 160.1 L·m^-2·h^-1,BSA rejection rate of 99.3%,and FRR of 92.3%.It can maintain a stable FRR in three cycles of ultrafiltration cycle experiments,indicating that PEN-COOH-60%membrane has excellent anti-fouling durability.4.In the treatment of printing and dyeing wastewater,PEN-COOH tight ultrafiltration(TUF)membrane prepared in this chapter has high-efficiency separation performance of dye/salt mixed solution.PEN-COOH TUF membrane owned a surface average pore size of 7.7 nm,the molecular weight cut-off was 3.1×10~4Da,the hydration permeability coefficient was 2.9 L·m^-2·h^-1·bar^-1,PWF was 401.2 L·m^-2·h^-1.It can completely reject negatively charged dyes(CR,CBB,EB),while the removal rate of salts(Na Cl,Na2SO4)does not exceed 10%.Taking CR as the model contaminant,the FRR of PEN-COOH TUF membrane was as high as 89%,showing excellent anti-dye-fouling performance.With the increased number of ultrafiltration cycle experiments,the FRR of the membrane remained basically stable,indicating that PEN-COOH TUF membrane had durable anti-dye-fouling performance.