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

A thermodynamic model was developed for representing vapor-liquid equilibri a (VLE) of the CO2-H2S-MEA-MDEA-water system. The model accounts for chemic al equilibria in the liquid phase and physical equilibria between the liqui d and vapor phases. Activity coefficients are represented by the electrolyt e-UNIQUAC equation. The present extension uses an ion-pair interaction appr oach and satisfies both the principles of like-ion repulsion and local elec troneutrality. Contributions from Iona-range ion-ion interactions are repre sented by a Debye-Huckel formula suitable for mixed solvents, water and alk anolamines. Adjustable parameters of the electrolyte-UNIQUAC equation, repr esenting short-range binary interactions, were determined by data regressio n using binary, ternary, and quaternary system VLE data. Predicted H2S and CO2 vapor pressures are in good agreement with the reported experimental da ta for aqueous solutions of a single acid gas as well as mixtures of H2S an d CO2 in MEA and MDEA and their mixtures in the temperature range 25-120 de greesC. (C) 2001 Elsevier Science B.V. All rights reserved.