Carbon dioxide absorption into unpromoted and borate-catalyzed potassium carbonate solutions

Potassium carbonate based solvents have the potential for capturing CO2 from emission sources such as power stations burning fossil fuels. However, due to poor reaction kinetics a rate promoter is considered necessary to improve the rate of reaction of CO2 with the solvent. Using a characterized wetted-wall column, we have studied the reaction kinetics of CO2 into unpromoted and borate-promoted 30 wt% potassium carbonate solutions. Results presented here show that, at 80 °C, addition of small amounts of boric acid (0.2 M, 0.6 M and 1.5 M) accelerate the overall absorption process of CO2 in carbonate solvents by 3%, 10% and 29% respectively. The Arrhenius expression for the reactions CO2 + OH− and CO2 + B(OH)4− are kOH [M−1 s−1] = 2.53 × 1011 exp(−4311/T [K]) and kborate [M−1 s−1] = 5.5 × 1011 exp(−6927/T [K]); and the activation energies are 35.8 kJ mol−1 and 57.6 kJ mol−1 respectively. Experiments were conducted between 40 °C and 80 °C and at a bulk partial pressure of CO2 of 90 kPa.

► Unpromoted K2CO3 solutions have a relatively slow rate of reaction with CO2.
► Boric acid improves the rate of reaction between CO2 and K2CO3.
► A wetted wall column has been characterized and used to measure rate constants.