Preparation And Characterization Of Anion Exchange Membranes Applied For Electrodialysis Desalination And Acid Recovery

Electrodialysis（ED）is an efficient,clean and economical membrane separation technology,which has been highly regarded and widely used in various fields of water treatment such as seawater desalination and waste acid recovery.Anion exchange membrane（AEM）,however,as the key material of ED technology,is still suffering from its lack of performances,such as short lifetime and non-ideal balance between the ion conductivity and permselectivity of AEMs applied for ED desalination,serious proton leakage and poor separation efficiency of AEMs applied for ED acid recovery.Aiming at the problems above,new ED AEMs for desalination and acid recovery were designed and prepared,and ED tests were carried out on them.The results are as follows:（1）Two kinds of ED desalination AEMs functionalized with hexyl-modified series-connected bipyridine and 1,4-diazabicyclo[2.2.2]octane（DABCO）di-cations（QPPO-DP and QPPO-DABCO respectively）were prepared via reactions of brominated poly（2,6-dimethyl-1,4-phenylene oxide）（BPPO）and the self-designed quaternization agents containing mono-ionic bipyridine and DABCO moieties respectively.QPPO-DP and QPPO-DABCO with similar functionalization degrees were characterized in terms of ion exchange capacity（IEC）,water uptake（WU）,swelling ratio（SR）,morphology,thermal and mechanical stabilities,area resistance（R_m）,transport number（t^-）,limiting current density,etc.,and were further applied in ED desalination tests.The aliphatic heterocyclic structure of DABCO di-cation offers QPPO-DABCO high IEC(2.63 mmol g^-1)and moderate WU（10.56%）,ensuring its outstanding ion conductivity（R_m=2.77Ωcm²）and permselectivity（t^-=0.95）.Thus,QPPO-DABCO showed more excellent ED performances than those of commercial AMX under the same ED conditions,including current efficiency of 89.58%,salt flux of 81.39 mg m^-2 s^-1 and reasonable energy consumption of 1.76 k Wh kg^-1.（2）A series of long-side-chain-modified tadpole-type AEMs named QPEK-DMODAs with microphase separated structures for ED acid recovery were fabricated from N,N-dimethyloctadecylamine（DMODA）as quaternization agent and poly（arylene ether ketone）（PEK）as polymer backbone,which is the copolymer of 2,2’,6,6’-tetramethyl biphenol（TMBP）and 4,4’-difluorobenzophenone（DFBP）.QPEK-DMODAs were characterized in terms of several basic properties and were further applied in ED recovery tests of H₂SO₄.As the WU rises with increasing IEC,QPEK-DMODA-3 with highest IEC(2.09 mmol g^-1)shows WU of56.01%.Such high WU brings side-effects to mechanical stability,ion conductivity and permselectivity of the AEM indeed,nevertheless,it is still controlled within reasonable range by the combination of hydrophobic backbone and alkyl side chains.As a result,QPEK-DMODA-3 exhibited higher current efficiency（54.58%）than those of QPEK-DMODA-1,QPEK-DMODA-2 and commercial AMX under the same ED conditions.Moreover,the Fe²⁺removal rate of QPEK-DMODA-3 reached 88.74%when it was applied for the ED recovery of0.50 M H₂SO₄ solution containing 0.10 M of Fe²⁺.