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Reaction mechanism and modeling study for the oxidation by SO 2 of o ‐xylene and p ‐xylene in Claus process
Author(s) -
Sinha Sourab,
Raj Abhijeet
Publication year - 2018
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.25583
Subject(s) - chemistry , radical , reactivity (psychology) , isomerization , photochemistry , benzene , toluene , catalysis , m xylene , claus process , reaction mechanism , xylene , medicinal chemistry , organic chemistry , sulfur , medicine , alternative medicine , pathology , hydrogen sulfide
Claus process, comprising of a furnace and a catalytic unit, is used to produce sulfur from H 2 S. The aromatic contaminants (benzene, toluene, and xylenes) in H 2 S 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 SO 2 (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 SO 2 to them. The breakage of OS bond in the xylyl‐SO 2 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 SO 2 than dimethylphenyl radicals. The reaction rate constants were found using transition state theory. The reactor simulations reveal that p‐ xylene has lower reactivity toward SO 2 than o‐ xylene, and CO, SO, and CHO are the main by‐products of oxidation.