Selective H₂S Absorption in Aqueous Tertiary Alkanolamine Solvents: Experimental Measurements and Quantitative Kinetic Model

Abstract

In the treatment of many fuel gases such as biogas, natural gas, syngas, and so on, tertiary alkanolamines play an important role in the selective removal of H 2 S with respect to CO 2 . The selectivity might be required for various reasons: to respect more stringent H 2 S specifications, to optimize the performance of the Claus unit, to lower the cost of CO 2 capture, and so on. The H 2 S/CO 2 selectivity is mainly kinetic and, to a lesser extent, thermodynamic. A novel experimental setup has been put in place to measure the time evolution of the simultaneous absorption of H 2 S and CO 2 . The results of an extensive experimental campaign with 18 different aqueous tertiary alkanolamine solvents (13 mol % amine, 87 mol % H 2 O) are presented. Although the absorption of H 2 S is expected to be a very fast proton transfer, a significant variation in H 2 S absorption rates and thus in selectivity is observed. This could not only be explained by the pK a or the viscosity of the amines. Therefore, an accurate quantitative molecular simulations-based kinetic model is developed and validated. The study allowed us to better understand the molecular origin of selectivity, as well as to identify amines with a higher selectivity than aqueous MDEA (MethylDiEthanolAmine), the standard industrial selective solvent.

Inhibition of Aqueous Chemical Reactions by Strong Liquid Structure Makers: Experimental Demonstration with Amides and Acid–Base Reactions

“…Figure shows the results for H 2 S. The absorption of H 2 S in aqueous MDEA (and in aqueous MDEA with EG) is very fast; it is controlled by the diffusion of H 2 S in the gas phase . The absorption of CO 2 is slower (see Figure ); it is controlled by the chemical reaction in the liquid phase .…”