# 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
Using data from the development of highly exothermic catalytic processes, in particular, processes of combustion of organic fuels in fluidized catalyst bed reactors [145; 146; 147; 148], a new technology using highly concentrated hydrogen sulfide-containing gas was proposed, the essence of which consists of a reaction conducted in a fluidized bed catalytic reactor-Modification 1 (Figure 14). Due to moderate temperatures (250-320 \({}^{\circ}\)C) applied in this technology, no hydrocarbon cracking reactions were observed. Thus, hydrogen formation seems unlikely. This assumption was confirmed by the results of the pilot and industrial tests, that showed:  
1. The preservation of qualitative and quantitative composition of hydrocarbons, and
2. The absence of hydrogen in the reaction products after the reactor. The primary source, which is potentially dangerous from the viewpoint of explosion safety, is the catalytic reactor in which the formation of hydrogen sulfide mixtures at explosive concentrations (i.e., 4.3-45.5 vol.% in the air) is possible. However, this problem is minimized by the following factors:  
Figure 13: Proposed mechanism of H\({}_{2}\)S oxidation on oxide catalysts. 1. Hydrogen sulfide is almost completely removed on the first three dm of the catalyst bed; that is, its concentration drops significantly, i.e., to below the explosion limit. 2. The reaction proceeds solely on the surface of the catalyst, so the transition of the process into the reactor volume proceeding according to the homogeneous chain (explosive) mechanism is excluded. Thus, the catalyst bed acts essentially as an effective flame arrester. A feed of hydrogen sulfide-containing gas is supplied to the reactor via a fluidized catalyst bed. 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 [49; 149; 150; 151; 152; 153]. At the same time, there is a treatment problem, i.e., a low pressure drop is required in the reactor, for gases with low concentrations of hydrogen sulfide, such as the tail and ventilation gases of various chemical industries, as well as the purification of energy carriers, such as oil-associated gases and geothermal steam where the pressure loss is extremely undesirable. To solve these problems, the reaction was conducted in the reactor with a monolithic catalyst with a honeycomb structure (process modification 2, Figure 15). Such catalysts have some advantages, in particular a low pressure drop and a high ratio of the outer surface area to volume [154]. Technologies have been tested on a pilot and experimental industrial scale, and their abilities to clean various gases containing hydrogen sulfide have been demonstrated (Tables 2 and 3, Figures 16-20).