Modelagem da solubilidade de CO2 e H2S em soluções de aminas via modelo de Kent-Eisenberg

Abstract

Natural gas and refinery gas conditioning requires the removal of carbon dioxide (CO2) and hydrogen sulfide (H2S), contaminants that affect operational safety, equipment integrity and environmental performance and must comply with strict quality limits established by Brazilian regulation for commercial gas. In this context, thermodynamic models able to represent, with reasonable accuracy and moderate complexity, the solubility of acid gases in aqueous amine solutions are key tools for the design and optimization of gas sweetening units. This work aims to model the equilibrium between CO2, H2S and aqueous solutions of monoethanolamine (MEA) and diethanolamine (DEA) using the Kent–Eisenberg model, formulated with apparent equilibrium constants and effective Henry coefficients regressed from experimental data. The methodology is based on the numerical implementation of chemical-equilibrium relations, elemental balances and electroneutrality, coupled to vapour–liquid equilibrium equations, and on the iterative solution of this system for different acid-gas loadings, temperatures (25 – 140 °C) and solvent concentrations representative of industrial operation (15 – 40 % m/m). Model validation was carried out by comparing simulation results with solubility data from the literature for aqueous MEA (15.3 wt% at 40 °C) and DEA (19.3 wt% at 40 °C) solutions in the presence of CO2 and H2S simultaneously. The results show satisfactory quantitative agreement, with average deviations of 6% for H2S and 16% for CO2 in MEA, and consistent performance for the DEA system, with average deviations of 12% for H2S and 10% for CO2. The equilibrium curves correctly reproduce the increase in partial pressure with temperature and gas loading, as well as the higher relative solubility of H2S compared with CO2. Predicted pH trends and speciation patterns are physically consistent and highlight the different roles of carbamate and bicarbonate in primary and secondary amines. It is concluded that the Kent–Eisenberg model satisfactorily describes CO2 and H2S solubility in MEA and DEA over the analysed operating ranges, providing a consistent basis for process design and for improving the energy and environmental performance of acid-gas removal units.