Preparation of cobalt-containing polyvinylimidazole ionic liquid catalyst and coupling with persulfate for room-temperature ultra-deep desulfurization

Poly-ionic liquid catalyst has both the advantages of ionic liquid and polymer, and overcomes the poor fluidity of ionic liquid, so it has become one of the hot spots in catalytic oxidative desulfurization. A polyvinyl-3-butylimidazolium cobalt chloride salt (poly-[BVIM][CoCl 3 ]) ionic liquid catalyst was prepared and characterized. When coupled with potassium monopersulfate (PMS), the catalyst formed a catalytic oxidative desulfurization system. The results showed that the prepared poly-[BVIM][CoCl 3 ] system had a microsphere morphology with a diameter of 28 μm, and the interior structure was a mesoporous structure formed via the self-assembly of two-dimensional thin-layered nanowires with a carbon skeleton width of 20 nm. The specific surface area was 10.54 m 2 ·g −1 , the pore volume was 0.029 cc·g −1 , and the average pore diameter was 3.5 nm. The optimum experimental conditions were: a catalyst dosage of 20 mg, 0.4 g of PMS (20 %) as oxidant, a reaction temperature of 20 °C, 2 g of acetonitrile as extractant, simulated sulfur-containing oil with dibenzothiophene (DBT) concentration of 500 ppm, and an initial sulfur content of 6 g. After 20 min, the sulfur removal reached more than 99 % and remained over 90 % even after the catalyst was recycled five times. The desulfurization sequence for different organosulfur compounds was DBT greater than 4,6-dimethyl dibenzothiophene (4,6-DMDBT) > benzothiophene (BT). The main desulfurization product was determined to be DBTO 2 by GC–MS analysis, and the speculated desulfurization mechanism was that Co(II) catalyzed PMS to form ·SO 4 − , which then oxidized the target molecules. The extraction-catalytic-oxidative desulfurization kinetic was established and verified that the desulfurization process accorded with zero-order reaction kinetics. The reaction rate constant ( k p ) for the production of ·SO 4 − was estimated to be 4.24 × 10 −9  ppm −1 ·min −1 .