Modeling of Partial Oxidation of Hydrogen Sulfide over Metal Oxide Catalysts

Abstract

In practical implementation of partial oxidation of hydrogen sulfide, it is of prime importance to determine the maximum allowable inlet hydrogen sulfide concentration, above which a thermal explosion in the reactor occurs. For this purpose, the dependence of the ignition temperature on the inlet temperature should be found. In its turn, this requires one to construct a mathematical model of the process that would allow for the change in the amount (the number of moles) of the reaction mixture, and for the thereby induced additional heat and mass transfer. Approaches that are necessary for constructing such models fundamentally differ from those needed for formulating the standard kinetic model of the process. The mechanism of catalytic partial oxidation of hydrogen sulfide has been studied in the reaction over activated carbon [1] and metal oxide catalysts [2, 3]. Different hypotheses of the reaction mechanism have been put forward, the kinetics parameters of the reaction have been found, and various kinetic equations for this process have been proposed. In this study, we developed an unsteady mathematical model of a fluidized-bed catalytic reactor and, on the basis of this model, performed a computational experiment, thus determining the starting conditions, and the effect of the main technological parameters on the process. Partial oxidation of hydrogen sulfide yields water and elemental sulfur. The process takes place at temperatures of 200—280ie and contact times of 1‐4 s. Under these conditions, sulfur is produced in the form of finely divided solid particles. A part of the sulfur formed is retained in the adsorbed state on the active surface of the catalyst and deactivates it. The other part is desorbed into the gas phase to form the species S 2 , which then polymerizes into the species S 4 , S 6 , and S 8 [4]. All the finely divided species are in equilibrium. Three possible mechanisms of the hydrogen sulfide oxidation were examined, which allow for (a) dissociative adsorption of oxygen, (b) hydrogen sulfide adsorption, and (c) simultaneous adsorption of oxygen and hydrogen sulfide. Collation between calculated and experimental data showed that the scheme (a) fits the experimental data well enough and, thus, can be used for the mathematical modeling of the reactor. The scheme (a) of the chemical reactions over a metal oxide catalyst has the form: