Preparation and Characterization of Ion Exchange Membranes for Diffusion and Fuel Cell Application

摘要

Membrane-based separation and purification technology is well-known in the industrial sector for its promising potential to recover both acid and bases from waste solutions.However, to accomplish the separation process with high efficiency we must need to have thermally, mechanically and chemically stable, reliable ion exchange membranes(IEMs).Therefore, fabrication of IEMs with high stability is itself an area of intense research. On the other hand Anion exchange membrane fuel cells (AEMFCs) can be treated as the most effective technology, which can produce clean energy.In this aspect too, the technology demands high-performance AEMs with improved physicochemical parameters.
　　In this current thesis we have mainly focused on the development of different ion exchange membranes, which included different polymerization techniques and polymeric structures (e.g.poly-condensation, free radical polymerization, comb-shaped architecture etc.).The goal of our study was to successfully design the synthetic routes for the preparation of high-performance membranes with improved flux, separation performances.Additionally, preparation of AEMs with high hydroxide ion conductivity and low water uptake was given huge preference.
　　SPPO-based blend membranes were prepared for base recovery.A highly sulfonated monomer was successfully synthesized via multiple steps and termed as 4,4'-(((((3,3'-disulfo-[1,1'-biphenyl]-4,4'-diyl)bis(oxy))bis(4,1-phenylene))bis(azanediyl))bis( methylene)) bis(benzene-1,3-disulfonate) [DSBPB].This monomer was further effectively blended with SPPO to produce the desired membranes.Prepared membranes were used for base recovery and we observed that it possess better base recovery performance than the parent unmodified SPPO membrane.Additionally separation performance was also satisfactory.Even after leaching, prepared membranes showed their potential character for base recovery. Thermo-mechanical stability of prepared membranes was remarkable.
　　PVA-based membranes were prepared for both base and acid recovery from industrial waste solutions.For base recovery purpose, we prepared a silica based 5-aminoisophthalic acid (AIPA) monomer and have been successfully introduced inside the PVA-backbone via sol-gel chemistry to develop its charged nature.The charged membranes were stable for the diffusion dialysis experiment.The prepared hybrid membranes showed moderate base recovery and good separation performance.
　　In case of PVA-based acid recovery two different cases can be seen.In first case, we designed the polymer Poly(DMAEM-co-γ-MPS) which contains a silica source and tertiary nitrogen.This polymer was prepared via a free radical polymerization reaction between DMAEM and γ-MPS with the help of the initiator named AIBN.The silica source available inside the polymer structure helped the sol-gel reaction with PVA and hybrid membranes can be formed.Finally, the charge nature was developed inside the membrane by the quaternization reaction done by EPTAC in the heterogeneous phase.Prepared membrane showed far better acid recovery performance (almost 7.25 times higher) than the commercial anion exchange membrane DF-120B.Also, the separation factor was ～3.5 times better than DF-120B, which is a remarkable aspect.Also the stability of the prepared membrane was satisfactory.
　　The second case with PVA-membrane involved quaternized aromatic amine based monomer.The monomer named QBAPB was successfully prepared and introduced inside the PVA backbone by poly-condensation reaction.In this case TEOS was used as a silica source. The presence of double quaternary ammonium groups gave us the privilege for obtaining good acid recovery performance (than commercial DF-120B).The separation performance was also better than commercial AEM DF-120B.Prepared membranes were thermo-mechanically stable.
　　BPPO-based comb-shaped AEMs with imidazolium cationic head groups possessing a long pendant alkyl chain at side chain were fabricated by grafting a novel monomer named HLTEI on hydrophobic BPPO backbone via Menshutkin reaction.The preparation of HLTEI involved thiol-ene click reaction performed under UV light and nitrogen atmosphere.The long alkyl chain gave rise to the desired comb-shaped morphology, which is particularly beneficial for hydroxide conduction.Prepared membranes were thermally and mechanically tough.The obtained results indicated that prepared membrane possess the anticipated qualities like high hydroxide conductivity and low water uptake.Hence, with these membranes the technical challenge related to conductivity and water uptake dilemma can be significantly overcome.Additionally, the alkaline stability of the prepared membranes in a challenging basic environment showed better performance than the traditional main chain type QPPO membrane.Therefore prepared membranes are potential candidates for the AEMFCs application.This thesis has shown the development of ion exchange membranes based diffusion dialysis process for base and acid recovery and also the unique way for the preparation of novel comb-shaped high-performance AEMs.