Reaction mechanism and modeling study for the oxidation by SO2 of o‐xylene and p‐xylene in Claus process

Abstract

AbstractClaus process, comprising of a furnace and a catalytic unit, is used to produce sulfur from H2S. The aromatic contaminants (benzene, toluene, and xylenes) in H2S feed form soot, and clog and deactivate the catalysts. Xylenes are known to be the most damaging ones. Therefore, there is a need to oxidize them in the furnace to enhance catalyst life. This article presents a kinetics study on the oxidation of o‐ and p‐xylene radicals by SO2 (an oxidant that is already present in the furnace) using density functional theory and a composite method. The mechanism begins with H‐abstraction from xylenes to form xylyl radicals, followed by exothermic addition of SO2 to them. The breakage of OS bond in the xylyl‐SO2 adducts leads to the loss of SO molecule, while the remaining O atom on them helps in their oxidation. The isomerization study shows that less‐stable dimethylphenyl radicals have a high tendency to isomerize to resonantly stabilized methylbenzyl radicals. However, methylbenzyl radicals have lower reactivity toward SO2 than dimethylphenyl radicals. The reaction rate constants were found using transition state theory. The reactor simulations reveal that p‐xylene has lower reactivity toward SO2 than o‐xylene, and CO, SO, and CHO are the main by‐products of oxidation.