Preparation,Performance Research And Application Of Composite Ion Exchange Membrane

Separation membranes play an important role in production and life,and separation and purification processes based on different membranes are constantly increasing in industrial applications and life.These membrane-related processes are economically feasible due to low energy consumption and easy-to-scale module designs.In recent years,ion exchange membranes have made important contributions to overcoming issues related to energy and the environment.The electrolytic manganese industry produces a large amount of ammonium sulfate residue every year.The accumulation of these waste residues not only wastes land resources,but also causes environmental pollution."Double-membrane and three-chamber"tank electrolysis technology is a green,environmentally-friendly and cost-effective method for treating ammonium sulfate waste.Ion exchange membrane is one of the core components of"double-membrane and three-chamber"tank electrolysis equipment.Polyvinylidene fluoride?PVDF?has very strong toughness,corrosion resistance,aging resistance,radiation resistance,and heat resistance.PVDF is used as the film substrate,N,N-dimethylformamide is used as the solvent,and styrene is used.As a graft,divinylbenzene?DVB?is used as a cross-linking agent,benzoyl peroxide?BPO?and/or azobisisobutyronitrile?AIBN?is used as an initiator,and PVDF is prepared by solvent evaporation and sulfonation Cation exchange membrane.Then,a composite PVDF cation exchange membrane?PVDF/SH-SiO₂?was prepared by adding nano-SiO₂ surface modified with 3-mercaptopropyltriethoxysilane.The membrane structure and membrane performance of PVDF cation exchange membranes are affected by the difference and content of initiators.Scanning electron microscopy?SEM?and Fourier transform infrared spectroscopy?FTIR?analysis of the micromorphology and chemical structure of the film found that BPO as an initiator can make styrene self-polymerize to form long chains and form DVB cross-linking with linear polymer PVDF The semi-interpenetrating network structure improves the compactness of the film;AIBN as an initiator can make styrene replace the H or F atoms on the PVDF carbon atoms directly grafted onto the linear PVDF chain.When BPO and AIBN are used at the same time,the semi-interpenetrating network structure due to BPO and the direct grafting effect due to AIBN improve the membrane performance.When the BPO content is 0.2%and the AIBN content is 0.4%,the ion exchange capacity?IEC?of the prepared ion exchange membrane reaches a maximum of 1.55 mmol/L,the moisture content reaches a maximum of 55.46%,and the membrane resistance also reaches a minimum of 4.2.When the BPO content was0.2%and the AIBN content was 0.2%?PVDF-4?,the migration number of the prepared ion exchange membrane reached a maximum of 94.85%.The cyclic voltammetry curve verified that the PVDF-4 film had a higher selective permeability,and the chronopotentiometry curve verified that the PVDF-4 film had a higher selective permeability and a lower film resistance.Based on PVDF-4 membrane,a composite PVDF cation exchange membrane was prepared using nano-SiO₂?SH-SiO₂?surface modified with 3-mercaptopropyltriethoxysilane.FTIR analysis revealed that 3-mercaptopropyltriethoxy silicon could be substituted for some of the hydroxyl groups on the surface of nano-SiO₂ after hydrolysis to complete the modification.Through SEM analysis,it was found that the nano-SH-SiO₂ particles have good dispersibility in the film matrix,have a good combination with the film matrix,and have a denser film structure and no agglomeration after mixing.The blending of nano-SH-SiO₂particles significantly improved the performance of the composite film.The IEC,moisture content,migration number,and fixed charge concentration of the composite PVDF cation exchange membrane all increased with the increase of nano-SH-SiO₂ particle content,and the membrane resistance decreased with the increase of nano-SH-SiO₂ particle content.When the doping ratio of nano-SH-SiO₂ particles is 2.0%,the composite PVDF cation exchange membrane has an IEC of 1.79 mmol/g,a water content of 52.46%,a migration number of96.1%,and a membrane resistance of 2.4.The application research of electrolysis of ammonium sulphate solution in the"double membrane three chamber"tank was carried out by using self-made membrane and commercial membrane in the laboratory.The study found that the electrolysis efficiency produced by using laboratory-made membranes for electrolysis is higher and the power consumption is lower.The electrolysis efficiency obtained by using PVDF/SH-SiO₂-4membranes is 91.23%and the power consumption is 1.547W?h/g.This is because the PVDF-4 membrane and PVDF/SH-SiO₂-4 membrane made in the laboratory have lower membrane resistance and higher ion selective permeability.