(417c) Catalytic Kinetics of Dibenzothiophene Oxidation with the Combined Catalyst of Quaternary Ammonium Bromide and Phosphotungstic Acid

A combined catalyst of quaternary ammonium bromide and phosphotungstic acid was used for dibenzothiophene (DBT) oxidation with hydrogen peroxide as the oxidant. The interaction between oxidized phosphotungstic acid and quaternary ammonium bromide was investigated and the kinetic parameters were estimated. The oxidized phosphotungstic acid is extracted from the aqueous phase to the interface by quaternary ammonium bromide due to a first order extraction. What is more, extraction capacity of different quaternary ammonium bromide is found to be similar to each other. It is confirmed that mass transfer of DBT from the organic media towards interface, rather than the mass transfer of the oxidized phosphotungstic acid, is rate limiting. Kinetics study indicates that reaction order towards DBT is 0.48 and the rate constant decreases in the order octadecyltrimethylammonium bromide > cethyltrimethylammonium bromide > (1-tetradecyl)trimethylammonium bromide > dodecyltrimethylammonium bromide. An empirical equation was established for predicting reaction rate constant. Based on the kinetic study, the catalyst at the interface is observed to have greater effect on DBT oxidation compared with the one in aqueous phase. Apparent activation energy Ea of 28.70 kJ/mol is obtained under the experimental condition.