The determination of the Henry’s Coefficient of reactive gases – An example of CO2 in aqueous solutions of monoethanolamine (MEA)

Abstract The Henry’s Coefficient of CO 2 is a fundamental property, it quantifies the equilibrium between the partial pressure of CO 2 in the gas phase and the concentration of dissolved free CO 2 in the liquid phase. This value is critical for simulation and may lead to improvements in the process of post combustion capture of CO 2 . However, because of its reactive nature, CO 2 reacts in amine solutions and forms multiple carbon-containing species, so that the free CO 2 concentration is very small and difficult to determine. The “N 2 O analogy” has been used to estimate the physical solubility of CO 2 based on the assumption that the two gases behave similarly in water and amine solutions. In the current study, a direct way is proposed for the determination of the Henry’s Coefficient of CO 2 in MEA solutions. The method only requires vapor-liquid equilibrium (VLE) measurements of the MEA-CO 2 -H 2 O system; and all equilibrium/protonation constants for all solution reactions are sourced from the open literature while activity coefficients for all ionic species were estimated using the Davis equation. The free CO 2 concentration in solution can be computed using the total MEA concentration, total CO 2 concentration and temperature, which allows the determination of the Henry’s Coefficient from the CO 2 partial pressure. A 10-parameter polynomial is used to approximate the Henry’s Coefficient as a function of the total MEA concentration, total CO 2 concentration and temperature. VLE calculations were performed using the liquid-phase equilibrium calculations and the polynomial function calculating the Henry’s Coefficient, and the results show the VLE calculations are adequate to describe the VLE data.