Preparation And Characterization Of Anion Exchange Membranes For Acid Recovery

Most of processing industries produce huge amount of acidic waste solutions containing heavy metal ions harmful to environment. Indeed, search of environmental friendly techniques to treat acidic waste solutions has become a hot research topic. Among proposed separation techniques, diffusion dialysis is the most promising method not only to separate the acid solution constituents but also to recover metal ions. Diffusion dialysis unique advantages include flexible operation and low energy consumption. However, an ion exchange membrane is a key component dictating the performance of diffusion dialysis. In development of diffusion dialysis for acid recovery, recent researches focus on developing high performance anion exchange membrane with high H+ ion dialysis, high separation coefficient and high thermal stability as well as low cost. In this paper, we proposed and fabricated three different approaches for developing high performance AEM. (1) The green route for the preparation of anion exchange membrane for diffusion dialysis, which used polyvinyl alcohol (PVA) as raw materials to prepare anion exchange membranes. (2) Anion exchange membrane with low cost and high performance is prepared with polyvinyl chloride (PVC) based on the semi interpenetrating network technology.(3) Anion exchange membrane with auxiliary group is exploited and its effects on diffusion dialysis is studied. Both of these works provide anion exchange membranes with good properties for acid recovery via diffusion dialysis. Accordingly, the micro-structures of the anion exchange membrane were characterized and as well the relationship between membrane microstructure and the performance of diffusion dialysis are discussed. The main conclusions drawn from this study are as follows.(1) Polyvinyl alcohol (PVA) and glycidyl trimethyl ammonium chloride (EPTAC) used as starting materials while aminopropyltriethoxysilane (KH550) acted as a crosslinking agent. A series of membranes were prepared by varying the content of EPTAC. The obtained membranes were characterized in terms of ion exchange capacity (IEC), water uptake (WR), linear expansion ratio (LER), tensile strength (TS), elongation at break (Eb), thermal decomposition temperature (Td) and initial decomposition temperature (IDT), etc. Their diffusion dialysis (DD) performance was conducted with a simulated feed containing 0.81M HCl+0.18M FeCl2. The results showed that the membranes not only have good chemical/thermal stability, but also possess high DD performance. The dialysis coefficients (Uh) are in the range of 0.011-0.018 m/h and the separation factors (S) are in the range of 18.5-21 at 25℃, both are higher than those of the commercial DF-120 membrane (0.009 m/h for UH, 18.5 for S) determined at the same conditions. Considering its low cost and easy fabrication, the route for hybrid anion exchange membranes provides better candidates in DD process for acid recovery.(2) Branched polymer named as allyltrimethylammonium chloride (TMA) was grafted on Polyvinyl alcohol (PVA) chain by free radical polymerization in water. A series of branched polymer hybrid membranes are prepared with branched polymer and Tetraethoxy-silicone (TEOS) acted as a cross-linking by sol-gel reaction. The obtained membranes were characterized with ion exchange capacity (IEC), water uptake (WR), linear expansion ratio (LER), tensile strength (TS), elongation at break (Eb), thermal decomposition temperature (Td) and initial decomposition temperature (IDT), acid resistance etc. Their diffusion dialysis (DD) performances are tested with a simulated feed containing 0.81M HCl+0.18M FeCl2. Research shows that diffusion dialysis coefficient (UH) is between 0.0168-0.060 m/h and the separation factor (S) is in 7.8-22.5, which are better than commercial membrane DF-120 (0.009 m/h for UH, 18.5 for S). As long as the grafting rate is appropriate, anion exchange membrane with excellent performance for diffusion dialysis can be obtained and the preparation process is basically green and simple.(3) Semi-interpenetrating polymer networks (sIPN) based on anion exchange membranes for acid recovery process were fabricated by immobilizing polyvinyl chloride (PVC) in dimethylaminoethyl methacrylate (DMAM) and divinylbenzene (DVB) copolymer (P(DMAM-co-DVB)). Prepared membranes were fully characterized in terms of FTIR, TGA, ion exchange capacity (IEC), wateruptake (WR), etc. Membrane structure and performance can be tuned by varying the content of PVC and dosage of cross-linking agent as well. Consequence of PVC content plus the cross-linking degree on ion permeability and selectivity was discussed in brief. Results revealed that the prepared membranes possess excellent thermal and acid stability due to the incorporation of chemically stable PVC matrix and the formation of sIPN morphology. Acid dialysis coefficients (UH) appeared in the range of 0.012-0.040 m/h and separation factors (S) ranged from 36 to 61 at 25℃. These obtained values are much higher than that of commercial membrane DF-120 (0.009 m/h for UH,18.5 for S). This methodology can be effortlessly scaled up and the obtained membranes could be an encouraging candidate for the acid recovery process via diffusion dialysis.(4) The anion exchange membrane was fabricated by the reaction of Brominated Polyphenylene Oxide (BPPO) and tertiary amine containing hydroxyl group Prepared membranes were fully characterized in terms of FTIR, TGA, ion exchange capacity (IEC), water uptake (WR),linear expansion ratio (LER) etc. At the same time, acid recovery performance by diffusion dialysis technique is tested. Obtained result shows that the acid recovery performance of the prepared membrane is excellent. It has been observed that hydroxyl group working as an assistant functional group can effectively improve the acid recovery performance by diffusion dialysis.