Optimization of oxidative desulfurization of Malaysian Euro II diesel fuel utilizing tert-butyl hydroperoxide-dimethylformamide system

Abstract

Deep oxidative desulfurization of model diesel consisting of thiophene, dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was investigated with various oxidants followed by extraction step using dimethylformamide (DMF). Response surface methodology based on Box-Behnken design was used to evaluate the effects of the main operating parameters, including the oxidant to sulfur molar ratio (2.0-4.0), oxidation temperature (40-60 °C) and oxidation time (10-60 min), on the 4,6-dimethyldibenzothiophene conversion. Among the oxidants used; tert-butyl hydroperoxide (TBHP) was led to the highest oxidation of model sulfur compounds. Meanwhile, the statistical results revealed that TBHP/sulfur ratio was the most important parameter followed by oxidation time and oxidation temperature. The optimum oxidative desulfurization conditions for 4,6-DMDBT conversion had been attained at TBHP/sulfur ratio of 3.0, temperature of 48 °C and period time of 31 min, respectively with the highest conversion of 4,6-DMDBT of 84.5%. The experimental optimum yield fitted-well with the predicted value with less than 5% error. The mechanistic study showed that the reaction between TBHP and 4,6-DMDBT was efficient to produce corresponding sulfoxide, instead of sulfone compound.