Selection of solvents for integrated CO2 absorption and electrochemical reduction systems

Abstract

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.