Development Of BPPO-Based Anion Exchange Membranes For Electrodialysis And Diffusion Dialysis

Electrodialysis(ED)is a mass separation phenomenon employed for the production of potable water,desalination of brackish water,water softening,and removal of other charged contaminations from water stream.On the other hand,diffusion dialysis(DD)is environment friendly ion-exchange membrane(IEM)separation technique used for the separation and recovery of acids.Therefore,highly stable IEMs are needed to achieve this goal.Our present work emphases on the development of homogenous and porous BPPO-based AEMs for electrochemical applications.A series of BPPO-based homogeneous AEMs were developed using N-methylmorpholine as ion-exchange content in the membrane matrix for ED applications by solution-casting method.The resulting AEMs were thermally and mechanical stable.Moreover,they showed higher chemical stability than quaternized poly(2,6-dimethyl-1,4-phenyl oxide)(QPPO)in the alkaline medium at room temperature.They showed higher ion exchange capacity(IEC)of 0.39-1.72 mmol/g and water content(WR)of 7.28-27.4%essential for ED application.They exhibited higher transport number(0.96)and lower ionic resistance(1.5 ?.cm2).The developed BPPO-based AEMs with higher ion-exchange contents in the polymer matrix showed higher desalination results than commercial membrane Neosepta AMX under same experimental conditions.Similarly,BPPO-based homogeneous AEMs were developed employing dimethylethanolamine as ion-exchange content for desalination applications.They showed IEC of 0.66-1.38 mmol/g,WR of 11.60-48.50%,volume expansion ratio(VER)of 8.58-20.21%,tensile strength(TS)of 32.52-49.22 MPa.and transport number of 0.94-0.98.They showed higher alkaline stability than quaternized poly(2,6-dimethyl-1,4-phenyl oxide)(QPPO)in alkaline medium at ambient temperature.Prepared homogeneous AEMs exhibited higher desalination performance than our previous prepared membranes and commercial membranes Neosepta AMX under identical experimental conditions.Moreover,porous AEMs were fabricated from BPPO and dimethylaniline by phase-inversion method.They showed higher thermal stability.They exhibited IEC of 0.34-0.82 mmol/g,WR of 202-226%,dimensional stability of 1.50-2.60%,and contact angle of 59.18°-65.15°.The prepared AEMs showed acid diffusion coefficient(UH)value of 0.0016-0.14 m/h which is higher than commercial membrane DF-120 at ambient temperature.On other hand,we have also fabricated porous AEMs from BPPO and triphenylamine(TPA)for diffusion dialysis(DD)applications by phase-inversion method.The successful development of these membranes was proved by FTIR spectra analysis.They have higher thermal stability.Further,they showed water uptake of 159.3-243.5%,IEC of 0.97-1.49 mmol/g,linear expansion ratio(LER)of 3.23-6.45%,and fixed group concentration of 0.0051-0.0061 mol/L.The change in morphology of developed AEMs with varying the concentration of TPA in the polymer matrix was investigated.Moreover,the dependence of morphology and DD performance on gelation medium of prepared AEMs was studied.They showed higher acid recovery(UH=0.010 m/h)at ambient temperature.Besides,the value of acid diffusion coefficient for prepared AEMs was decreased with increasing the ethanol concentration in the gelation medium.Moreover,the preparation of homogeneous BPPO-based AEMs for acid recovery via DD was also carried out by solution-casting method.They revealed higher thermal,mechanical and chemical stability.They possess higher IEC of 1.94-2.38 mmol/g,WR of 22.99-41.49%and LER of 6.38-11.10%.The scanning electron microscopy(SEM)and atomic force microscopy(AFM)was used for investigation of membranes morphology.The prepared membranes showed higher acid recovery at room temperature.This thesis has provided the shortest routes for the development of AEMs for electrodialysis and diffusion dialysis applications which will be useful in future.