Zeolite-catalyzed chlorination of toluene by sulfuryl chloride: Activity, selectivity and deactivation of NaK-L zeolite

Chlorination of toluene using SO₂Cl₂ as chlorinating agent and NaK-L zeolite as catalyst was studied. A kinetic model was generated to model the initial kinetics of the reaction. It assumes equilibrated adsorption of toluene as the most abundant surface intermediate and reaction between adsorbed toluene and solution phase sulfuryl chloride as the rate-determining step. The initial para-selectivity varies with reactant composition, being greatest at the highest SO₂Cl₂ concentrations. The catalyst deactivates rapidly with use, and is only partially regenerated by an elevated temperature oxidation treatment. Loss of para-selectivity accompanies the deactivation and is not restored by the oxidative regeneration treatment. The regenerable activity loss is attributed to accumulation of residues on the surface and within the catalyst pores, the irreversible activity loss is attributed to de-alumination of the zeolite framework leading initially to pore blockage by ext ra-framework aluminum and precipitated salts and ultimately to structural degradation.