(670b) A Two-Dimensional Transport Model of Bipolar Membrane Electrodialysis for the Electro-Regeneration of Carbon Capture Solvents.

Bipolar membrane electrodialysis (BPMED) is an emerging electrocatalytic reactor technology which uses an electric field to split water. A major application of BPMED is the electrochemical solvent regeneration of solutions used in CO2 capture. Protons generated within bipolar membranes are used to shift the acid-base equilibria back to gaseous CO2, providing a more sustainable alternative to thermal regeneration when integrated with renewable electricity sources.

Despite its potential, current limitations to BPMED implementation stem from a large power consumption and high membrane costs. In addition, gas bubbles in solution can cause high electrical resistances, experimental studies of which are challenging. To address this, we present a two-dimensional model of BPMED for CO2 capture solvent recovery in COMSOL Multiphysics. The Navier-Stokes and continuity equations were implemented to compute a convection field, and the ionic species transport calculated through Nernst-Planck equation with an electroneutrality condition. A concentration source term accounted for ionic speciation and water splitting reactions, captured through kinetic rate expressions and the second Wein effect. Experimental validation conducted on a PC Cell BED 1-4 recirculating batch system demonstrated good agreement between the model and experimental results across a range of conditions and variables.

The calculated concentration profiles revealed that the majority of the speciation reaction takes place inside or directly adjacent to the bipolar membrane. Crucially, this includes the conditions necessary for bubble nucleation. Bubbles consequently form inside membrane pores, displacing the electrolyte and greatly increasing the electrical resistance of the membrane. However, the location of the reaction plane where bubbles are generated can be manipulated by increasing the channel width or reducing the applied voltage. The strength of this model has therefore been demonstrated to identify and explore engineering challenges in BPMED. Future research will focus on expanding to multiphase CFD simulations to investigate the coupled effect on flow.