Reactive Absorption of Carbon Dioxide in l-Prolinate Salt Solutions

Aqueous amino acid salt solutions are seen as more sustainable alternative CO2 solvents compared to conventional alkanolamines. The absorption of CO2 into aqueous solutions of potassium l-prolinate, over the temperature range of 290–303 K, was studied using a stirred cell. To compare the effect of potassium versus sodium as counterion, the absorption rates of CO2 in sodium l-prolinate solutions were also determined. The amino acid salt concentration was varied between 0.5 and 3 mol dm–3. Physicochemical properties such as density, viscosity, and physical solubility of N2O, required in the interpretation of absorption rate experiments, were determined separately. The obtained experimental reactive absorption fluxes were interpreted, using the pseudo-first-order approach, into intrinsic reaction kinetics. The potassium-based solvent showed, on average, a 32% higher reactivity toward CO2 than the sodium equivalent. The kinetic data were correlated in a power-law reaction rate expression. The reaction order with respect to the amino acid was found to be between 1.40 and 1.44 for both l-prolinate salts, and the second order kinetic rate constant, k2, was calculated for the potassium salt to be 93.7 × 103 dm3·mol–1·s–1 at 298 K with an activation energy of 43.3 kJ·mol–1. l-Prolinate salts show higher chemical reactivity toward CO2 than most of the amino-alcohols and amino acid salts.