Study of Calcium-Based Sorbents for High-Temperature H2S Removal. 2. Kinetics of H2S Sorption by Calcined Limestone

Abstract

Samples of calcined limestone particles having a diameter of about 1 mm were exposed to simulated coal gases containing between 500 and 18 000 ppm H2S for temperatures ranging from 560 to 1100 °C in a differential tube reactor. The formation of CaS was followed quantitatively as well as qualitatively to elucidate the reaction mechanism. Contrary to the limited conversion of CaCOs to CaS, it was found that the limestone particles could be completely converted to CaS by 1% H2S in about 1 h if the particles are precalcined or if the rate of calcination is higher than the rate of sulfidation. The reaction then takes place between CaO and H2S and follows a shrinking-core mechanism. The reaction kinetics is controlled by the diffusion of H2S through the pores of the CaS product layer formed around the lime particle (effective diffusivity between 2.8 x 10-6 and 5.1 x 10-6 m2/s). The kinetics of the sorption of H2S by CaO is relatively insensitive to the reaction temperature, and the reaction rate does not decrease significantly when the CaO is severely sintered for several hours at 1050 °C prior to sulfidation.

Simultaneous Production of High-Purity Hydrogen and Sequestration-Ready Co2 From Syngas

“…The layers were allowed to mix for several minutes at forty times minimum fluidization velocity, but complete mixing was never achieved. (38) The dissociation occurs from the outside surface inward, usually along uniform, concentric areas between the CaCO 3 and the newly formed CaO. Figure 25 illustrates the influence of carbon dioxide concentration and pressure on the dissociation temperature of CaCO 3.…”

“…Fenouil [36][37][38] Borgwardt [40] determined that the combined effects of H 2 O and CO 2 on the sintering of CaO at a given temperature were greater than the summative effect of each gas alone, and surface area loss was more strongly affected than porosity. It was determined that grain boundary and surface diffusion mechanisms were responsible.…”

Surface interaction of H2O and H2S onto Ca12O12 nanocluster: Quantum‐chemical analyses

“…21 The X 12 Y 12 cages have been extensively investigated to assess their applications as adsorbent for different analytes. In our recent works, 26,[29][30][31]35,36 44,45 Low activation energy of 21.59 kJ/mol was obtained for these reactions via thermogravimetric analysis. 6 Furthermore, the heat of adsorption amounts to 81 ± 22 kJ/mol, indicating that the adsorption of H 2 S on CaO belongs to the category of entropically ideal site adsorption.…”

“…CaO has also received considerable interest in fundamental research because of its wide availability in natural minerals. The kinetics of the reactions between H 2 S and calcined limestone (CaO + H 2 S → CaS + H 2 O) have been experimentally examined . Low activation energy of 21.59 kJ/mol was obtained for these reactions via thermogravimetric analysis .…”

Development of a regenerable calcium-based sorbent for hot gas cleanup

“…From their results the authors suggested that Model 2 best describes the kinetics of both reactions. Fernouil and Lynn (1995b) also studied the kinetics of the reaction between calcined limestone and H2S gas. In their work 20 -30 mg of 1.75 mm limestone particles were used.…”