Predicting Speciation of Ammonia, Monoethanolamine, and Diethanolamine Using only Ionic Radius and Ionic Charge

This study investigates the speciation of CO 2 involving the most common solvents used to capture carbon from flue gas, i.e. ammonia, monoethanolamine (MEA), and diethanolamine (DEA). This requires the knowledge of both the activity coefficients of the species involved and the equilibrium constants of the relevant reactions. In contrast to the equilibrium constants, which can be obtained from the literature, the activity coefficients of the aqueous species are required to be estimated. Normally, semiempirical models are used to estimate these activity coefficients, i.e. equations that contain unknown parameters that are obtained through regression against experimental data. In contrast, in this study the activity coefficients are predicted using equations that require only the knowledge of the ionic radii and charges of the species involved in the equilibrium. As a conclusion, the model developed shows very good agreement with the experimental data obtained, either from spectroscopy or from vapor-liquid equilibrium (VLE), up to a solvent mass fraction of 20%.