Benzene destruction in claus process by sulfur dioxide: A reaction kinetics study

Benzene, toluene and xylene (BTX) are present as contaminants in the H ₂S gas stream entering a Claus furnace. The exhaust gases from the furnace enter catalytic units, where BTX form soot particles. These particles clog and deactivate the catalysts. A solution to this problem is BTX oxidation before the gases enter catalyst beds. This work presents a theoretical investigation on benzene oxidation by SO₂. Density functional theory is used to develop a detailed mechanism for phenyl radical -SO₂ interactions. The mechanism begins with SO₂ addition to phenyl radical after overcoming an energy barrier of 6.4 kJ/mol. This addition reaction is highly exothermic, where a reaction energy of 182 kJ/mol is released. The most favorable pathway involves O-S bond breakage, leading to the release of SO. A remarkable similarity between the pathways for phenyl radical oxidation by O₂ and its oxidation by SO₂ is observed. The reaction rate constants are also evaluated to facilitate process simulations.