Formation of polycyclic aromatic hydrocarbons in Claus process from contaminants in H2S feed gas

Claus process is used in oil and gas industry to produce sulfur from H2S. The presence of aromatic contaminants in its feed is believed to have detrimental effect on the process, as they are able to survive the high-temperature environment of Claus furnace and reach the catalytic units, where they form soot, clog catalyst pores, and deactivate them. Along with aromatics, small hydrocarbons (CH4, C2H6, and C3H8) are also present in feed that are capable of forming polycyclic aromatic hydrocarbons (PAHs) and soot in anoxic, high-temperature environment of the furnace. In this work, a detailed reaction mechanism with 258 species and 1695 reactions for Claus feed containing H2S, aliphatic and aromatic hydrocarbons, CO, CO2 and H2O is developed. The mechanism includes reactions for PAH formation (up to coronene) from hydrocarbons, H2S oxidation, and the interaction of hydrocarbons with S-containing species. The mechanism is validated using experimental species and aromatics profiles in flames. Through furnace simulations, the fate of aromatic contaminants, the amount of PAHs formed from hydrocarbon contaminants and the temperature effects on PAH profiles are determined. The PAH formation pathways are found, and the role of resonantly stabilized radicals is highlighted.