Kinetics and reaction mechanism of catalytic oxidation of low concentrations of hydrogen sulfide in natural gas over activated carbon

The kinetics of the hydrogen sulfide oxidation process, producing mostly sulfur and water, was studied using 0.25 to 1.0 g Hydrodarco activated carbon catalyst and varying the O-2/H2S ratio (molar basis) in the feed gas between 0.5 to 0.6 in the temperature, and pressure ranges From 125 to 200 degrees C and 225 to 780 kPa, SO2 was obtained as an undesirable by-product during H2S oxidation reaction or as a product during regeneration of the catalyst. The feed gas contained 0.9 - 1.3 mol% H2S with approximately 80 mol% CH4. In this paper, the factors affecting the H2S conversion and SO2 formation are presented. The rate expressions for (a) H2S conversion and (b) SO2 formation were developed from the Langmuir-Hinshelwood surface control reaction model. The experimental data were well correlated by the rate equations. Also, the rate parameters were evaluated and correlated with temperature. The activation energies for H2S oxidation and SO2 production reactions were calculated to be 34.3 and 62.5 kJ/mol, respectively. Partial pressures of oxygen acid H2S were found to influence H2S conversion whereas, the presence of water in the feed gas up to 10.5 mol% did not affect H2S conversion significantly. Heats of adsorption for various species on the active sites were calculated. SO2 production was, as expected, enhanced at higher temperature, and its rate was much smaller than the oxidation rate of H2S under the reaction conditions used.