Adsorption behavior and kinetics of H2S on a potassium-promoted hydrotalcite. (8th November 2018) - Coenen, Kai
Abstract: Adsorption of H2 S and the influence of steam on its adsorption capacity and kinetics were studied on a commercial potassium-promoted hydrotalcite. The sorbent shows a very high cyclic working capacity for H2 S compared to CO2 and H2 O, even at lower partial pressures and at different operating temperatures ranging between 300 and 500 °C. The operating temperature does not significantly influence the cyclic working capacity for half-cycle times of 30 min. The adsorption mechanism, however, changes at higher temperatures. At lower temperatures (300 °C) a fast adsorption with a fast approach to steady state was observed. At higher operating temperatures, H2 S reacts with the hydrotalcite structure, forming strongly bonded sulfuric species on the sorbent. When using dry regeneration conditions, the first cycles in cyclic operation at higher temperatures show a significantly higher adsorption of H2 S (especially the first cycle), which cannot be desorbed during regeneration with N2 . After the first fast initial adsorption rate a continuous slow adsorption of H2 S occurs, probably caused by a surface reaction between H2 S and the hydrotalcite structure. This reaction is, however, reversible if steam is used. The adsorption mechanism for H2 S and H2 O was determined using multiple cyclic experiments comparable to previous studies performed for CO2 and H2 O adsorption. It is evident that the adsorption mechanism developed for CO2 on the same sorbents is also valid for H2 S, indicating that the developed mechanism is consistent for sour gas adsorption on this type of sorbents. The cyclic working capacity can be significantly increased if steam is used during the regeneration step of the sorbent. The mechanistic model developed for the adsorption of CO2 and H2 O was successfully validated with more than 160 different TGA experiments. An operating temperature of 400 °C seems to be optimal to achieve a high cyclic working capacity for H2 S, because at higher temperatures the regeneration of the formed sulfuric species seems to be hindered resulting in a significant decrease in the cyclic working capacity. Graphical abstract: Highlights: TGA and packed bed reactor test were used to determine the working capacity and kinetics of sorbents. H2 S and the H2 O adsorption on a potassium promoted sorbent have been tested. Interaction between CO2 H2 S and H2 O has been studied. A reaction mechanism involving different adsorption sites for CO2 H2 O and H2 S has been developed.