Chemical Oxidation of Dibenzothiophene with a Directly Combined Amphiphilic Catalyst for Deep Desulfurization

A combined amphiphilic catalyst of octadecyltrimethylammonium bromide (STAB) and phosphotungstic acid was formed directly in a reaction system. Deep desulfurization of dibenzothiophene (DBT) with high selectivity was achieved using the combined amphiphilic catalyst with hydrogen peroxide (H2O2) as the oxidant at 50 °C under atmospheric pressure. The optimum molar ratio between STAB and phosphotungstic acid in DBT oxidation has been determined, and the highest reaction rate was obtained when the molar ratio between STAB and phosphotungstic acid approached 1, not 3 as has been reported in some literature, whereas superfluous STAB beyond this ratio caused resistance for mass transfer of products and reagents at the interface. The influence of reaction temperature, catalyst concentration, H2O2/DBT ratio, and mixing conditions on the oxidation of DBT was examined in detail. An increase in the reaction temperature from 40 °C to 70 °C led to a remarkable increase in the reaction rate. A complete DBT conversion with a DBT concentration of 3000 ppm could be shortened to 10 min as the temperature was elevated to 70 °C. The reaction rate of DBT was improved when the H2O2/DBT ratio was increased. Complete sulfur removal from a 3000 ppm dibenzothiophene mixture was achieved within 20 min at 50 °C. This oxidation process showed high selectivity toward DBT, and the enhancement of DBT oxidation was illustrated when investigated in the presence of 2-methylnaphthalene.