Abstract: In this study, a transition metal catalyst (phosphotungstic acid) and quaternary ammonium salts (tetramethylammonium chloride) immobilized on magnetic particles (iron oxide), knowing as composite catalyst, were synthesized. This composite catalyst was used to conducted an ultrasonic-assisted oxidation test for the pure organic sulfur compounds (Dibenzothiophene, DBT).
The premilitary results indicated that the composite catalyst has the best oxidation efficiency while the ratio of polyoxometalate/phase transfer catalyst on iron oxide is 3:1 (0.6 g: 0.2 g). When the loading ratio is maintained at 3:1, the oxidation effect is significantly improved after the dosage is increased five times (3.0 g: 1.0 g), and the DBT oxidation efficiency reaches 76.6%. Moreover, the amount of hydrogen peroxide added has a significant effect on the reaction effect. When the volume ratio of hydrogen peroxide to DBT is 2:1 (12 mL: 6 mL), the best DBTO oxidation efficiency of 54.5 ppm can be obtained. However, excessive addition leads to inhibition of the reaction.
The oxidation experiment optimized by Box-behnken Design, the experimental parameters obtained are: hydrogen peroxide: DBT = 18:6, catalyst dosage 0.8 g, reaction time 10 minutes, which can achieve the best oxidation efficiency, and the DBT oxidation rate reaches 100%. Moreover, in the recovery test of this composite catalyst after the reaction, the recovery efficiency of the composite catalyst in the first recovery was about 50%, and after the second and third recovery after the oxidation reaction, the recovery efficiency can reach 70-80%.
This composite catalyst illustrated a desulfurization efficiency superior to that of traditional methods in both treated and untreated oil products, reaching 46.2% and 42.2% desulfurization efficiency respectively, indicating that it has good application potential and practicality for medium and low sulfur content oil products.