Manganese-based poly(ionic liquid)-catalyzed oxidative desulfurization

Abstract

The metal catalytic active centers in solid catalysts containing metal-based polymeric ionic liquids exist in an ionic state, significantly enhancing their catalytic efficiency. In this study, a desulfurization catalyst, vinyl-3-butylimidazolium manganese chloride ionic liquid, is synthesized through the polymerization of approximately six monomers. This desulfurization catalyst is combined with the oxidant potassium peroxymonosulfate (PMS) and the extractant acetonitrile (ACN) to remove dibenzothiophene (DBT) from octane. In a reaction involving 20 mg of the catalyst, 1 g of PMS, 1 g of ACN, and 6 g of simulated oil containing 600 ppm DBT at 20 °C, the DBT removal efficiency reaches 99%. Furthermore, after six cycles of use, the desulfurization rate remains as high as 90%. GC-MS analysis reveals that the desulfurization products are DBTO and DBTO₂. The oxidation mechanism primarily involves Mn²⁺ in the catalyst losing electrons to activate HSO₅⁻, generating sulfate radicals (˙SO₄⁻), which oxidize the sulfur atom in DBT. HSO₅⁻ also facilitates the cyclic transformation among Mn²⁺, Mn³⁺, and Mn⁴⁺. Based on the desulfurization mechanism, the reaction kinetics for this catalytic oxidative desulfurization process are established. This desulfurization process is a zero-order reaction, with a reaction rate constant between Mn²⁺ and HSO₅⁻ of 0.09173 ppm mg⁻¹ min⁻¹ g⁻¹, and the activation energy for catalytic desulfurization is 35.62 kJ mol⁻¹.