Hydrocarbon formation with toluene in thermal stage of claus process

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% C₇H₈₇ 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.