Performance Optimization of Bipolar Membrane Electrodialysis of Ammonium Sulfate/Bisulfate Reagents for CO2 Mineralization

This paper reports on tests performed with the dual aim of minimizing the energy use (kilojoules per kilogram) and maximizing the conversion rate (kilograms per hour) of bipolar membrane electrodialysis (BPMED) for the regeneration of chemicals needed for the effective scale-up of the accelerated CO ₂ mineralization route developed at Åbo Akademi University (ÅA). The performance of two- and three-compartment stacks was compared with ammonium sulfate (AS) and ammonium bisulfate (ABS) as the input product feed, yielding sulfuric acid and aqueous ammonia, respectively, as the final products. It was shown that a two-compartment stack is more efficient with regard to energy use (i.e., electricity consumption), with values in the range of 3630-4844 kJ/kg of AS or ABS, compared to the three-compartment stack requiring 5102-7223 kJ/kg of AS or ABS. A maximum conversion rate of ∼0.13 kg/h was achieved with the two-compartment stack. We also concluded that approximately 25% of the energy needed for the process may give off heat, depending primarily on the voltage applied to the membrane stack. A two-compartment stack will require fewer membranes, which is an obvious benefit in terms of maintenance and cost. Furthermore, we concluded that AS provides a more efficient conversion than ABS, when considering both energy use and the amounts of the solution that need to be recycled in the BPMED step.