Predictions of the solubility of acid gases in monoethanolamine (MEA) and methyldiethanolamine (MDEA) solutions using the electrolyte-UNIQUAC model

Abstract A thermodynamic model was developed for representing vapor–liquid equilibria (VLE) of the CO 2 –H 2 S–MEA–MDEA–water system. The model accounts for chemical equilibria in the liquid phase and physical equilibria between the liquid and vapor phases. Activity coefficients are represented by the electrolyte-UNIQUAC equation. The present extension uses an ion-pair interaction approach and satisfies both the principles of like-ion repulsion and local electroneutrality. Contributions from long-range ion–ion interactions are represented by a Debye–Huckel formula suitable for mixed solvents, water and alkanolamines. Adjustable parameters of the electrolyte-UNIQUAC equation, representing short-range binary interactions, were determined by data regression using binary, ternary, and quaternary system VLE data. Predicted H 2 S and CO 2 vapor pressures are in good agreement with the reported experimental data for aqueous solutions of a single acid gas as well as mixtures of H 2 S and CO 2 in MEA and MDEA and their mixtures in the temperature range 25–120°C.

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