A new theoretical thermodynamic model for the solubility of acid gases in aqueous solution of N-Methylidethanolamine

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

In gas sweetening, acid gases such as CO2 and/or H2S are usually removed by “chemical” absorption through aqueous amine solutions such as N-Methylidethanolamine (MDEA) solution. Reliable prediction of equilibrium properties (vaporliquid equilibrium and species distribution) is needed for a rigorous design of such absorption processes. Information on energy requirements can also be obtained from a reliable vapor−liquid equilibrium thermodynamic model. The currently used methods for correlating/predicting the simultaneous solubility of H2S and CO2 in aqueous MDEA solutions require accurate experimental solubility data of single and mixed gases, which, in general, confine their applicability in the experimental region. The purpose of this study is to develop a new theoretical thermodynamic model based on incorporating thermodynamic relationships that correlates the equilibrium and solubility constants to the Gibbs free energy of reaction, leading to an enhanced predictive capability of the model. In this work the Pitzer model is used to account for activity and specific ion interactive forces. This will allow to take into account the effect of the presence of all cations and anions such as thermally stable salts, dissolved organic species and amine degradation products that are usually encountered in absorption units. The suggested model can be a very powerful tool that could be of significant importance in the design of amine absorption processes as well as in simulations of the operating variables for optimization of gas sweetening systems.