# Direct Selective Oxidation of Hydrogen Sulfide: Laboratory, Pilot and Industrial Tests
## 19 Description of Modern Industrial Methods Based on the Process of Direct H\({}_{2}\)S Oxidation
The adsorption of H\({}_{2}\)S on the surface of catalysts (Figure 11) led to the formation of two types of surface species: sulfates (I) at 1100 cm\({}^{-1}\) and (II) registered at higher frequencies 1264 and 1342 cm\({}^{-1}\), corresponding to organic sulfates. The sulfates of type (I) formed on \(\gamma\)-alumina at 100 \({}^{\circ}\)C, while type (II) formed at 250 \({}^{\circ}\)C. The formation of these two species was detected at much lower temperatures on Fe\({}_{2}\)O\({}_{3}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) and MgCr\({}_{2}\)O\({}_{4}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) due to their higher oxidative activity. Figure 10: IR spectra of adsorbed CO: initially and after H\({}_{2}\)S adsorption. Figure 9: Results of laboratory experiments on the separate oxidation of propane and hydrogen sulfide over a MgCr\({}_{2}\)O\({}_{4}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) catalyst (Catalyst: MgCr\({}_{2}\)O\({}_{4}\)/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\); residence time: 0.8 s; C\({}_{\rm{H2S}}\): 30 vol.%; C\({}_{\rm{C3H8}}\): 15 vol.%). The DRS study (Figure 12) revealed that various types of elemental sulfur, i.e., S\({}_{4}\)-S\({}_{8}\), formed on the catalyst surface during the reaction depending on the nature of the catalyst. Based on the data obtained, the reaction mechanism for the direct oxidation of hydrogen sulfide can be represented by the schematic depicted in Figure 13.  
In the first stage, the hydrogen sulfide is adsorbed on the surface of the catalyst. The adsorption can occur (i) through the participation of the LACs and the sulfur atom of the hydrogen sulfide molecule, (ii) through the participation of the BACs and the sulfur atom with the formation of hydrogen bonds, or (iii) through the participation of a particular catalyst center, e.g., surface oxygen and the proton of the H\({}_{2}\)S molecule. The adsorption on Lewis acid centers leads to the greatest activation of the hydrogen sulfide molecule. Next, the hydrogen sulfide molecule adsorbed on the Lewis acid center can interact with a neighboring oxygen atom of the catalyst or a hydroxyl group. This process can lead to the dissociation of hydrogen sulfide molecules to form a hydroxyl group or water. Figure 11: IR spectra of samples of different catalysts after adsorption of 20 torr of H\({}_{2}\)S at various temperatures. Figure 12: Different sulfur species formed on the surface of catalysts after H\({}_{2}\)S oxidation, as detected by UV DRS (30 torr H\({}_{2}\)S, 1 h, T = 250 \({}^{\circ}\)C). The oxygen of the catalyst surface oxidizes the formed surface particles to form surface SO\({}_{2}\) groups, which, upon interacting with the hydrogen sulfide molecule from the gas phase or with an adsorbed hydrogen sulfide molecule, will yield the final reaction products, i.e., elementary sulfur and water, via the surface Claus reaction. A raw hydrogen sulfide-containing gas is supplied to the reactor with a fluidized catalyst. Simultaneously, oxygen (or air) is fed into the catalyst bed via a separate flow. Before the gas stream supply, the catalyst bed is heated to initiate the catalytic reaction. The excessive heat of the exothermic reaction of H\({}_{2}\)S oxidation is efficiently removed by a heat-exchanger in the fluidized bed. The bed temperature is maintained within the preset range (280-320 \({}^{\circ}\)C) with high uniformity by regulating the amount of heat removed from the bed with a heat-exchange agent. The technology was successfully tested on a pilot and industrial scale in Russia's largest sour gas fields, refineries, and gas processing plants. Developments of the Boreskov Institute of Catalysis SB RAS Regarding the Creation of Processes of Heterogeneous Catalytic Oxidation of Hydrogen Sulfide for the Treatment of Various Gases  
At the Boreskov Institute of Catalysis SB RAS, various technologies for direct catalytic oxidation of hydrogen sulfide have been developed.