Conventional configurations for alkanolamine and acid gas ar

Conventional configurations for alkanolamine and Okadaic acid gas are not suitable to represent the chemical reaction between acid gas and alkanolamines. Nevertheless, Dowell et al. [17] have successfully represented the phase behaviour of CO2-water-MEA systems by using SAFT-VR [18] without any consideration of electrolytes species. They proposed that chemical reactions can be treated as strong associating physical interactions. Association sites that allow the pseudo-chemical reaction of CO2 and MEA are introduced in Weirtheim part of SAFT. This approach has been successfully applied with SAFT-VR to estimate CO2 solubility in MEA, MDEA, DEA, AMP, DEtA as multifunctional alkanolamine [17] [19], and some n-alkyl amines [20]. Recently, they applied this approach in process simulation and optimization for CO2 capture by aqueous solution of MEA [21]. Their approach for treating the chemical reactions is employed in this study. However, the solvation between CO2 and water was neglected in their work. But according to Tsivintzelis et al. [22], the solvation effect between CO2 and water should be considered for representing the CO2 - water binary system. The effect of considering the solvation effect between CO2 and water for describing the multicomponent CO2–alkanolamine-water system is investigated in this work, see Appendix B: supplementary information. The results shows the solvation effect gives better results, and it lead to less temperature dependent on kij. In this paper, results are obtained by considering the solvation effect. A new conception of association schemes for acid gas and alkanolamines is developed and investigated in this work, as can be seen in Fig. 1. Fig. 1.a shows the association scheme for CO2, the e site is assigned as a solvation site which allows the cross association between CO2 and water, α1 and α2 are dedicated reaction sites which only react (cross-associate) with the electron site on alkanolamine. Depending on the nature of alkanolamine, 1 α site can be activated for MDEA, and 2 α sites are activated for MEA. Fig. 1.b is the association scheme for H2S, the two e sites are given as solvation sites which allows the cross association between H2S and water, α1 and α2 are dedicated reaction sites which only react (cross-associate) with the electron site on alkanolamine. Depending on the nature of alkanolamine, the α1 site is activated for MDEA, and both α1 and α2 sites are activated for MEA. Fig. 1.c is the association scheme of water and also the symmetric model of alkanolamine. There are four sites in total including: two e sites and two H sites representing different functional groups. In this symmetric model, there is no distinction between e and H sites, i.e. the association behaviour of the different functional groups are identical. Fig. 1.d is the asymmetric model of alkanolamine, one e* site is added based on the symmetric model of alkanolamine (4C) in order to distinguish the –NH from –OH functional groups (NH group reacts with CO2 and H2S).·In this asymmetric model, e* site on alkanolamine react only with the α sites on acid gas. The choice of symmetric and asymmetric models for alkanolamine has been investigated. The asymmetric model has been finally chosen because it gives significantly better results than the symmetric one, and this fact has been proved by Dowell et al. [20]. As an example, the reaction between MEA and CO2 can be represented by Fig. 2. Reaction products can be determined from a statistical analysis of the molecules not-bonded at given sites, by using Equations (3), (4):Where x is the molar concentration of total CO2 in the liquid phase in equilibrium, it is related to the concentration of alkanolamine and loading ratio and is the mole fraction of CO2 not bonded at αi site. For alkanolamine-acid gas mixtures, modified CR1 combining rules are applied, their cross-association volume and the cross-association energy are fitted from VLE experimental data:k is the binary interaction parameter in the van der Waals combining rule, and it is considered as an adjustable parameter. The influence of k and its temperature dependency will be studied in this work. , and k are considered as adjustable parameters. They are fitted simultaneously for acid gas-alkanolamine-water systems using ternary VLE data by minimizing objective function which is detailed in next the section.