Preparation of polymeric ionic liquid-coated magnetic nanoball catalyst and coupling peroxymonosulfate for catalytic oxidation desulfurization at room temperature

Abstract

A heterogeneous catalyst was prepared by wrapping a poly 3-butyl vinylimidazole cobalt chloride ionic liquid (P[BVIM]CoCl3) around the surface of Fe3O4@SiO2 magnetic nanoballs. This catalyst was coupled with the oxidant peroxymonosulfate (PMS) for extraction catalytic oxidation desulfurization (ECODS). The prepared desulfurization catalyst had superparamagnetic properties, with a saturation magnetization of 32.5 emu/g. Moreover, this caalyst was multi-porous material, ans it had a specific surface area and pore volume of 8.14 m2/g and 0.018 cc/g, respectively. The average pore diameter of catalyst was 3.9 nm. The optimal experimental conditions were as follows: the initial sulfur content of the oil was 500 ppm, the catalyst dosage was 30 mg, PMS (20 wt%) dosage was 0.6 g, the ACN dosage was 2 g, and the oil sample size was 6 g. After 20 min, a sulfur removal rate of over 98 % was achieved at 20 °C. Furthermore, the unpurified catalyst still maintained high desulfurization activity after being used for 5 times, demonstrating good stability. The desulfurization mechanism was divided into two steps: first, DBT was oxidized to DBTO by SO4− free radicals, and second, the DBTO was further oxidized to DBTO2 by OH free radicals in a tandem reaction. The reaction rates for the two steps at 20 °C were 0.0144 sec−1 and 0.00115 sec−1, respectively. The activation energies associated with these steps were 65.65 kJ/mol and 105.22 kJ/mol, respectively. The quencher t-butanol had no effect on the first step but significantly inhibited the second step, meaning that DBTO became the main oxidation product. One potential application of this study is the utilization of t-butanol to regulate the oxygen content in organic sulfide oxidation products.