Study On Interfacial Modification And Application Performances Of Ion Exchange Membranes

Membrane technology can achieve advance process intensification due to its own technical advantages,and has aroused extensive research interest in industrial processes such as fuel cells,seawater desalination,industrial wastewater treatment,and chlor-alkali industry.As the core component of this technology,ion exchange membranes(IEMs)should process high ion flux as well as ion selectivity to satisfies the practical application.And the performance of IEMs is closely correlate to the material itself and the inner microphase structure(matrix and interface),which can be optimized by the preparation and modification methods.Combing the application background(including energy,resources and environmental protection)of ion exchange membrane,this thesis investigates the influence of interface modification methods on the IEMs' performance.The details are as follows:(1)In order to prepared IEMs with ordered ion transport channel,the pore-filling strategy were applied to increase the ion conduction flux:To synthesize tertiary amine-ester-based copolymers,different ratios of dimethylaminoethyl methacrylate and methyl methacrylate monomers were polymerized through free radical polymerization.By the Menshutkin reaction between the tertiary amine group in the copolymer and the bromomethyl group on the porous brominated polyphenylene oxide,the pore interface of the membrane matrix was modified by pore filling,and the copolymers with different microphase structures were prepared.The valence bond triggers the channel-filled anion exchange membrane.Benefit from the Menshutkin reaction on the inner wall of the inherent sponge pore in the base membrane,the continuous through-plane ion channel was formed,which consisting of concentrated concertrated hydroxide transport active sites in the inner wall interface.The prepared IEMs showed high hydroxide conductivity(39.8 mS cm-1)and competitive H2/O2 fuel cell performance(peak power density of 315 mW cm-2 at 60?)at low IEC(0.97 mmol g-1).(2)In order to further improve ion selective conductivity of ion exchange membrane,surface interface modification was carried out.An anion exchange membrane grafted on the synthetic copolymer containing tertiary amines and ester groups,with the help of the strong oxidation of trifluoroacetic acid/ethanol solution,the anion permselective membranes with carboxyl polymer layer was formed by self-assembly after hydrolysis reaction on the membrane surface.The covalent bonding of the polymer cortex ensures its mechanical stability in the application process.And the abundant carboxyl groups distributed uniformly in the cortex guarantee its excellent ion selectivity in the process of electrodialysis desalination(the membrane with the highest content of carboxyl group,whose ion selectivity of Cl-/SO42-is up to 7.31,which is better than the commercial film ACS)and desalination performance.(3)In order to expand the application of ion-exchange membrane,a bipolar membrane was prepared by interfacial modification of the membrane.The copolymers containing tertiary amines and ester groups were hydrolyzed to copolymers with tertiary amine and carboxyl by trifluoroacetic acid.The catalyst is immobilized by coordination between functional groups(tertiary amines,carboxyl groups)of the polymer and iron ions.The polymer/catalyst composite was grafted on the anion-exchange layer BPPO by Menshutkin reaction to form a catalyst layer.This layer was further compounded with a cation-exchange layer sulfonated PPO(SPPO),and then quaternized to obtain a bipolar membrane.Thanks to the coordination between the copolymer and the catalyst to prevent the catalyst from leaking,a large number of free carboxyl groups on the intermediate layer of the polymer promote the efficient hydrolysis of the bipolar membrane,thus achieving efficient water dissociation efficiency and ultra-fast acid and alkaline production.(4)In order to develop new process applications of ion exchange membranes,ionic membrane actuators were prepared by polymer grafting.We grafted different polyelectrolytes containing tertiary amine groups onto the brominated polyphenylene oxide based membrane via Menshutkin reaction to prepare ionic membrane actuators with different morphologies and structures.The quaternary amine groups generated by the quaternization reaction and the hydrogen bonds existing in the membrane changed the hydrophilicity of the membranes.The change in hydrophilicity promotes changes in the swelling behavior of the membrane surface,thereby endowing the ionic membrane actuator with responsive behavior towards water vapor or water.