Production Of Organic Acids And Bases By Bipolar Membrane Electrodialysis

Bipolar membrane is a special ion-exchange membrane comprising an anion-exchange layer and a cation-exchange layer. It can dissociate water molecules into H+ and OH- with the lowest theoretical voltage drop under reverse bias in a direct current electric field. Integrating the function of bipolar membranes and conventional electrodialysis, bipolar membrane electrodialysis (BMED) can simplify many industrial processes and produce acid and/or base without second pollution, so it has been widely used as a sustainable technology in resource recycling, pollution control, cleaner chemical processing.In this thesis, bipolar membrane electrodialysis is adopted for production or recovery of organic acids and bases, i.e., the production of tetramethyl ammonium hydroxide (TMAH) and recovery of the mixed organic acids from vitamin B12 discharge. The main conclusions are as follows:(1) A one-unit BMED stack of BP-A configuration (BP, bipolar membrane; A, anion exchange membrane) was chosen to produce TMAH from tetramethyl ammonium chloride (TMAC). The results indicate that current efficiency increases and energy consumption decreases as feed concentration increases or current density decreases. The highest current efficiency can reach 99.9%, and the lowest energy consumption is 1.43 kWh kg^-1. Based on a 3-unit BMED, the process cost is estimated to be 0.33 $ kg^-1 of TMAH.(2) A one-unit BMED stack of BP-A-C configuration was used for recovery of mixed organic acids form vitamin B12 discharge. The concentration of electrolyte in the acid chamber has insignificant effect on BMED performance, and the greatest impacting factor is current density. With an increase in current density, both current efficiency and energy consumption decrease, and all the current efficiencies are above 85%. The process is estimated to be 0.0392 $ mol-1. After BMED treatment, the chemical oxygen demand (COD) of the discharge was reduced by 6000 mg(O2) dm^-3, so the following biological treatment can be easier.To sum up, production of TMAH and recovery of organic acids from vitamin B₁₂ discharge by using BMED are not only feasible but also cost-effective. Since the research was conducted on a laboratory scale, more work needs to do before industrialization.