A comprehensive study of CO2 solubility in aqueous 2-HEAA and MEA + 2-HEAA solutions – Measurements and modeling

Abstract

CO2 solubility in aqueous 2-(hydroxy)ethylammonium acetate (2-HEAA), aqueous monoethanolamine (MEA) and aqueous MEA+2-HEAA systems was measured using a static total pressure method. The measurements were conducted within 303–353K and 3.8–1300kPa temperature and pressure ranges, respectively. The 2-HEAA mass fraction range in the measured H2O+2-HEAA systems was 0.25–1. The mass fractions of H2O, MEA and 2-HEAA in the H2O+MEA+2-HEAA systems were 0.68–0.7, 0.15–0.30 and 0–0.15, respectively. Additionally, a thermodynamic activity coefficient model was developed to describe the systems mentioned above.The solubility of CO2 in aqueous MEA+2-HEAA solutions decreased as the 2-HEAA mass fraction increased. Thus, the formation of 2-HEAA through MEA degradation into acetic acid was found to decrease the CO2 capture capability of the aqueous MEA solution. A chemical equilibrium model was developed to correlate the experimental data. The model is based on the well-known chemical equilibrium between aqueous MEA and CO2. The computationally straightforward ionic activity coefficient model was used to include the effect of both MEA and 2-HEAA on the CO2 absorption. The model correlates the partial pressure of CO2 over all the measured data points, covering all the measured systems, with the average deviation of 23kPa. The absolute average deviation of the model was 6.8% for the data points measured at over 25kPa and 17% for all of the data points. In addition, the model was used to simulate CO2 solubility in aqueous benzoic acid+MEA systems by changing the acid dissociation constant to that of benzoic acid. The simulation results were in good agreement with the experimental values found in the open literature, demonstrating the models capability in describing the effects on CO2 solubility of various types of acidic impurities found in aqueous MEA solutions.