Alkanolamine processes are used in the industry to remove acid gases, like CO 2 , H 2 S and other sulphur components, from natural gas and industrial gas streams. In this process the acid components react with the basic alkanolamine solution via an exothermic, reversible reaction in a gas/liquid absorber. The composition of these amine solutions is continuously changed to optimise the (selective) removal of the several acid components. For the design of gas treating equipment accurate mass transfer, reaction kinetics and solubility data of acid gases in aqueous alkanolamine solutions are required. In this paper new solubility data of H 2 S and CO 2 in aqueous MDEA at different conditions encountered in modern gas treating facilities are presented. The experimental pressure and temperature were varied from 6.9 to 69 bar (methane was used as make-up gas) and from 10 to 25°C respectively. These new solubility data were evaluated and correlated with an Electrolyte Equation of State Model (EOS) as originally proposed by Fürst and Renon [Fürst, W., Renon, H., 1993. Representation of Excess Properties of Electrolyte Solutions Using a New Equation of State. AIChE J., 39 (2), pp. 335.]. The application of Equation of State Models for the prediction of VLE data for reactive, ionic systems is a rather new development in this field.

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Abstract:In this work the electrolyte equation of state as developed previously for the system MDEA-H 2 O-CO 2 -CH 4 [Huttenhuis et al. (2008), pp.99-112] was further developed for the system MDEA-H 2 O-H 2 S-CH 4 . With this thermodynamic equilibrium model the total solubility of hydrogen sulfide and the speciation in aqueous solutions of N-methyldiethanolamine can be described quantitatively. The model results were compared to experimental H 2 S solubility data in aqueous MDEA in absence and presence of methane respectively. The application of equation of state models for this kind of acid gas -amine systems is a rather new development in the literature. An accurate description is difficult for this kind of complex systems with significant amount of both molecular and ionic species present in the liquid phase. The Schwarzentruber's modification of the Redlich-Kwong-Soave EOS with a Huron-Vidal mixing rule is used as molecular part of the equation of state and ionic interactions terms are added to account for non-idealities caused by these interactions. With the new developed model a comparison with experimental data as presented was made.

In this work, 72 new experimental solubility data points for H2S and CO2 mixtures in aqueous N-methyldiethanol amine (MDEA) solutions at different methane partial pressures (up to 69 bara) are presented. They are correlated using an electrolyte equation of state (E-EOS) thermodynamic model. This model has already been used to estimate the CO2 solubility in aqueous MDEA ( Huttenhuis Fluid Phase Equilib.200826499112) and the H2S solubility in aqueous MDEA ( Huttenhuis Int. J. Oil, Gas Coal Technol.20081399424). Here, the model is further extended to predict the behavior of CO2 and H2S when they are present simultaneously in aqueous MDEA. The application of an equation of state is a new development for this type of system, i.e., of acid-gas−amine systems. The molecular interactions are described by Schwarzentruber et al.’s modification of the Redlich−Kwong−Soave equation of state, with terms added to account for ionic interactions in the liquid phase. The model is used to describe acid-gas solubility data for the CO2−H2S−MDEA−H2O system reported in the open literature and experimental data reported here for the CO2−H2S−MDEA−H2O−CH4 system.

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