Preparation And Characterization Of Poly(arylene Ether)s Anion Exchange Membranes For Electrodialysis

Anion exchange membrane（AEM）is the key component of electrodialysis（ED）device.Its property is closely related to ED performance.In order to solve the weak fundamental problem of AEM structural design for ED,the effects of AEM ion distribution and microstructure of AEM main chain on ED desalination behavior were studied.Details are as follows:1.The influence of ion distribution of AEM on the fundamental and ED performances.Took 4,4’-difluorodiphenyl sulfone（FPS）,bisphenol A（BPA）,octamethyl-FPS（8CH3-FPS）and tetramethyl-FPS（4CH₃-FPS）as monomers and synthesized the mother polymer with side-chain-ion structure.After that,the mother polymer was undergone bromomethylation and quaternization processes with N-bromosuccinimide（NBS）and trimethylamine orderly to obtain side-chain-type QPAESs QPAES-a and QPAES-b.Took FPS,BPA and 2,2,6,6-tetramethyl biphenol（TMBP）as monomers,then the main-chain-type QPAESs QPAES-c were obtained by a similar process.We tested and compared the ion exchange capacity（IEC）,water uptake,swelling ratio,ion conductivity,thermal stability,transport number and mechanism property among QPAESs with different ion distribution.Moreover,the ED desalination performances and current efficiency（η）of them were tested and calculated using a home-made ED device.The results indicated that QPAES-c which has the densest micro-structure gave out the best mechanism property,desalination performance and highestη.Its ED performance was even better than commercial AEM TWEDA1.2.The influence of the fine structure of AEM main-chain on the fundamental and ED performances.Based on the fact that main-chain-type structure is beneficial to the ED performance of AEM,we studied effect of the fine structure of AEM main-chain on its fundamental and ED performance.Took FPS,TMBP and 4,4’-difluorodiphenyl ketone（FPK）as monomers and obtained three different kinds of main-chain-type AEMs QPAEK,QPAEKS and QPAES after a similar procedure mentioned above.They had different backbones with different ketone/sulfone ratio.Their IEC,area resistance,and ED performance such asη,removal energy consumption per unit mass NaCl（EC）,salt flux（J）were calculated and compared with each other.The QPAEK having a ketone-type structure gave out the lowest EC value,attributed to its balance between resistance andη.Also,its comprehensive ED performance was better than that of TWEDA1.3.The influence of the concentration of diluting and concentrating compartments on ED device and the limit current density(i_lim)of ion exchange membranes（IEMs）,and the influence of current density on the ED performance.Took QPAEK as the research object,the i_lims of IEMs and ED device in different compartment concentrations were measured,and the influences of the separation from i_lim of operating current density were studied.The results showed when the operating current density is higher than i_lim,complete concentration polarization will happen and raise the resistance of the device.It causes a negative influence on the ED process.