Selection of solvents for integrated CO₂ absorption and electrochemical reduction systems

Solvent-based electrochemical CO₂ reduction (CO₂R) enables the production of chemicals or fuels using CO₂ from a preceding absorption process. Employing previously tested CO₂ capture solvents does not ensure their suitability for either CO₂R or integrated CO₂ absorption-reduction. We propose solvent selection criteria that include the CO₂ solubility, kinetic constant, ionic conductivity, concentration of the bicarbonate, carbamate, and solvent cation in the CO₂-loaded solution, and sustainability indicators. They are implemented for solvent selection (a) from novel, aqueous mixtures of N-methylcyclohexylamine (MCA) with piperazine (PZ), 2-amino-2-methyl-1-propanol (AMP), potassium hydroxide (KOH), and potassium chloride (KCl) and (b) from aqueous monoethanolamine (MEA), AMP, KOH, MCA, and PZ solutions. Versions of a modified Kent-Eisenberg model for strong bases, carbamate, and non-carbamate-forming amine solutions are developed and parameterized through experimental equilibrium measurements. CO₂R experimental results are presented for solutions of KOH and MCA + KOH, as these indicate desired trade-offs for CO₂ absorption and reduction.