# Direct Selective Oxidation of Hydrogen Sulfide: Laboratory, Pilot and Industrial Tests
## 9 Modifications of the Claus Process  
Research attempts have been made to optimize the Claus process (notably, the catalytic part). It has been proposed that the interaction of sulfur dioxide and hydrogen sulfide be carried out in the fluidized catalyst bed. Studies were carried out in a cylindrical reactor with an internal diameter of 0.1 m and a height of 0.86 m. Spherical active alumina of the Kaiser S-501 brand with an effective diameter of 195 \(\upmu\)m was used as a catalyst. The maximum concentration of the reagents were H\({}_{2}\)S-1300 ppmv and SO\({}_{2}\)-650 ppmv, and the test temperatures were 100-150 \({}^{\circ}\)C, that is, below the dew point of the sulfur. The fluidization number was varied in the range of 2.2-8.8. It was shown that the observed conversion of sulfur compounds was \(\sim\)96% in the initial period, although this decreased with an increase in sulfur sediments to 60% in 16 days of continuous operation. As the main advantages of the method, the authors note catalyst loading was reduced by up to 50% compared to the three-reactor scheme of the Claus process. The developed method could be considered as an alternative to the known processes of purification of tail gases based on sulfur condensation (CBA, Sulfreen) followed by the regeneration of catalytic material, and not a fundamentally new process for replacing the catalytic stages of the Claus process [44]. A process for the purification of hydrocarbon gas with hydrogen sulfide contents of 2.3-5 vol.% and carbon dioxide of 3-5 vol.% is proposed. The initial gas also contains from 40 ppmv to 90 ppmv benzene, toluene from 45 ppmv to 220 ppmv, xylene from 20 ppmv to 150 ppmv, carbon sulfoxide (COS) from 25 ppmv to 70 ppmv, heavy hydrocarbons (to C\({}_{50}\)), mercaptans from 15 ppmv up to 50 ppmv. The overall gas processing complex includes the amine treatment installation and the \"classic\" three-reactor scheme of the catalytic conversion of sulfur dioxide and hydrogen sulfide into elementary sulfur. In the proposed procedure, the gas stream coming from the amine treatment unit is split in a ratio of 75%/25%, and the larger flow enters the first zone, a specially developed furnace, while the smaller stream enters a flushing column after the catalytic converters. In the flushing column, at the interaction of the gas flow components with a caustic soda solution, selective absorption of carbon dioxide occurs, and the stream enriched in hydrogen sulfide flows into the second zone of the thermal stage of the total process line. Such technological approaches are specifically used to extend the lower limit of the range of hydrogen sulfide concentrations in the initial gas stream to 30%. Furthermore, according to the authors' statements, this method is an alternative to the COPE process, while the complex as a whole will ensure the following characteristics of the purified gas: the content of hydrogen sulfide in the purified gas is 4 ppmv, the carbon dioxide content is not higher than 1.7 vol.%; and the content of organic sulfur compounds is not higher than 60 ppmv. It should be noted that the proposed procedure was conceived via computer simulations, and did not undergo any testing on the pilot or experimental levels [45]. There are also proposals to increase the degree of hydrogen sulfide conversion by its removal from the tail gas using reagents based on triazines in order to neutralize residual H\({}_{2}\)S [46]. Researchers from Politecnico Di Milano developed a rather interesting concept, i.e., the simultaneous disposal of H\({}_{2}\)S and CO\({}_{2}\)[47]. With regard to the gasification process of coal, they proposed the joint utilization of acid gas components by reacting carbon dioxide and hydrogen sulfide according to the following Equation:  
\[2\mathrm{H}_{2}\mathrm{S}+\mathrm{CO}_{2}\rightarrow\mathrm{H}_{2}+\mathrm{ CO}+\mathrm{S}_{2}+\mathrm{H}_{2}\mathrm{O} \tag{14}\]  
In this case, carbon dioxide is used as a \"soft\" oxidizer.