Role of Toluene on Hydrocarbon Formation at Thermal Stage of Claus Process

Abstract

Experimental results on hydrocarbon formation during the combustion of hydrogen sulfide and hydrogen sulfide-toluene mixture in H2/O2-N2 flames under Claus conditions (Φ=3) are presented. Toluene is often present in acid gases (mainly H2S and CO2) from crude natural gas wells so that combustion of H2S/C7H8 mixture is of significant importance in Claus process that is used to recover sulfur and energy from acid gases. Role of toluene is isolated from direct comparison of the results from combustion of 100% H2S gas with that of 99% H2S/1% C7H8 gas mixture. The formation and destruction of hydrocarbons and other gas phase species during combustion of H2S and C7H8 mixture are presented. The results revealed decomposition of H2, H2S and the formation of SO2 during combustion of 100% H2S gas. Mole fractions of SO2 increased to an asymptotic value while simultaneously reducing the rate of formation of elemental sulfur. In contrast, combustion of H2S and toluene mixture reduced the rate of H2 oxidation and increased that of H2S, which is attributed to the additional amounts of H2 formation from toluene decomposition and also from the increased reactor temperature. This favored faster increase in SO2 formation to a peak mole fraction but the formed SO2 decomposed with axial distance along the reactor. The decay of SO2 is attributed to the reactions between SO2 and other sulfur containing radicals or formed hydrocarbons to produce elemental sulfur. Presence of toluene fostered the formation of methane, acetylene and carbon disulfide in the reactor. Rate of acetylene formation was observed to be faster than that of methane. Formation of carbon disulfide and hydrocarbons adversely impact the performance and efficiency of sulfur capture in a Claus process.