Synthesis,Structure And Property Of Anion Exchange Membranes For Electrodialysis

With the rapid expansions of industries and population growth,the restrictions of resources scarcity and environmental pollution confirm that developing high-efficiency technologies for resource recoveries and pollutant treatments has become increasingly urgent.As a membrane separation technology,electrodialysis(ED)desalination technology has displayed a surge in potential as highly efficient and environmental method for seawater desalination,sewage treatment,resource recoveries and food industry.As the core components of ED desalination devices,ion exchange membranes(CEMs and AEMs,respectively)with high ion exchange capacities(IECs),proper water uptakes(WUs),low swelling ratios(SRs),high ion conductivities,superior permselectivities,good chemical,mechanical and dimensional stabilities are desired,which is directly affect the electrodialysis desalination performance.From the perspective of molecular structure design,various hydrophobic components were introduced into poly(arylene ether sulfone)s(PAES)anion exchange membranes(AEM)to study structure-activity relationship between main chain structure and performance.Moreover,a series of novel AEMs with phase separation structure have been designed and synthesized by introducing long hydrophobic side chain,series-connected dications or series-connected dications appending flexible hydrophobic tails to poly(2,6-dimethyl-1,4-phenylene oxide)(PPO)in this paper,and study the variation in permselectivity and area resistant from the changes of structural and their effect on ED desalination property.The main contents are as following:(1)Three kinds of AEM with different hydrophobic structure and similar IEC value were prepared by introducing biphenol(BP),bisphenol A(BPA)and bisphenol fluorine(FBP)into PAES to study structure-property relationship between hydrophobic structure and AEM.The results show that the rigid copolymer unit(BP)with smaller space structure can lower WU,SR and R_m at excellent P value,which offer AEM with optimal ED performance.(2)A series of tadpole-type AEMs were prepared by introducing N,N-dimethyl octadecylamine(DMODA)introduced into PPO.The angle X-ray scattering(SAXS)and transmission electron microscopy(TEM)measurement indicated that the series of tadpole-type ionomers offer obvious nano-phase separation aggregate structures at the investigating IECs.When with IEC of 1.71 mmol/g,PPO-DMODA possessing the best AEM combination property and ED desalination performance with WU of 13.5%,SR of 3.8%,R_m of 2.8?cm~2,P of 95%,current efficiency(?)of 88.7%,salt flux(J)of 80.61 mg/(m~2 s)and energy consumption(EC)of 2.56 k Wh/kg.(3)Three forms of series-connected dication ionic ionomers(PPO-TMEDA-Me,PPO-DABCO-Me and PPO-DP-Me)designed for electrodialysis desalination(ED)anion exchange membranes have been synthesized successfully from monoionic quaternization agent aliphatic N-(2-(dimethylamino)ethyl)-N-trimethyl-1-aminium iodide,N-bridged 1-methyl-1,4-diazabicyclo[2.2.2]octan-1-aminium iodide,aromatic 1-methyl-[4,4'-bipyridin]-1-aminium iodide and BPPO.The TEM measurement proved PPO-TMEDA-Me with linear series-connected dication have more obvious nano-phase separation aggregate structures.AEM property and ED performance test results demonstrated that PPO-TMEDA-Me AEM with aliphatic series-connected dication possessing the best AEM combination property(R_m=1.92?cm~2,R_m=93.2%)and ED desalination performance(?=89.3%,J=75.39 mg/(m~2 s),EC=1.69 k Wh/kg)at the same of IEC.(4)A series of AEM with series-connected dications appending hexyl tails have been synthesized successfully from BPPO and a monoionic quaternization agent N-(2-(dimethylamino)ethyl)-N,N-dimethylhexan-1-aminium bromide.Our study convey that the appending hexyl tails can suppress the over enhanced water uptake resulted from the dense series-connected dications structure and enhance the ability of hydrophilic and hydrophobic nano-phase separation.Particularly,QPT-4 with IEC of 2.33 mmol/g at the family of QPTs offer lowest R_m(1.60?cm~2)and excellent P(94%),which possess WU of 14.1%,SR of 5%,current efficiency(?)of 89.14%,salt flux(J)of 75.57 mg/(m~2 s)and energy consumption(EC)of 2.16k Wh/kg.