Mass transfer and kinetics study on combined CO2 and SO2 absorption using aqueous ammonia

• Mass transfer and kinetics of combined CO2 and SO2 absorption in NH3 were studied.
• A bi-liquid film assumption was proposed to analyze the SO2 and CO2 absorption.
• The second-order reaction rate constant of CO2 matches well with the previous work.
• High SO2 concentration inhibits the CO2 mass transfer in liquid film.

Combined capture of CO2 and SO2 using aqueous ammonia (NH3) is a good option to reduce capital and operational costs for post-combustion capture process. The mass transfer and kinetics of combined CO2 and SO2 absorption in aqueous NH3 solvent were determined at various SO2 concentrations, temperatures and NH3 concentrations using wetted wall column. A bi-liquid film assumption was proposed to analyze the mass transfer and kinetic characteristics by dividing the liquid film to SO2 instantaneous reaction region and CO2 pseudo-first-order reaction region. The high SO2 concentration significantly reduces the CO2 mass transfer coefficient in overall liquid phase and the SO2 instantaneous reaction region, but the high temperature and aqueous NH3 concentration benefit the CO2 mass transfer. In the CO2 pseudo-first-order reaction region, the apparent and second-order reaction rate constants of CO2 absorption were calculated and the second-order reaction rate constant can match very well with the previous work.