Study On Oxidative Desulfurization From Gasoline By Phase Transfer Catalysis

To meet the environmental requirements,the production of low sulfur gasoline is the global refining industry development trend,and the research of desulfurization technology has an important practical significance.Oxidative desulfurization(ODS) with efficient process,reduced oxidative cost and environmental-friendly impact is attracting more and more attention.However,there are still some problems as to the insolubility of the polar aqueous phase and nonpolar organic phase which hinder oxidant and substrate of organosulfur to react with each other,thereby decreasing the reaction rate and lowering the conversion of organosulfur.Phase transfer catalysts(PTC) with their unique capability to dissolve in both aqueous and organic liquids have been used extensively in a variety of chemical applications.Oxidative desylfurization by phase transfer catalysts is a new type of environmental-friendly desulfurization process.In this paper,different catalytic systems under ultrasonic field to remove thiophene were exploited,and an insight study into the mechanism of oxidative desulfurizaiton by phase transfer catalysts was also exploited.As to the process of oxidative desulfurization,model compounds rather than the gasoline were studied firstly,and the results showed that the sulfur content in gasoline was below 30μg/g,far below the criterions of European and America.Investigation of the oxidative reaction time,temperature and the sorts of phase transfer catalysts were carried out.Oxidative desuifurization by phase transfer catalysts was investigated with thiophene or dibenzothiophene in n-heptane as the model compound of light oil.It was shown that the desulfurization rate of thiophene was 92.44%,under the conditions of water/oil ratio 1∶1,90min,40℃,with hydrogen peroxide/formic acid as the oxidant and TBAB as the phase transfer catalyst.From the kinetics' study,it was shown that the reaction was pseudo first-order reaction with rate constants of k₄₀℃=1.2672 h^-1.and the activation energy Ea=7.32 kJ/mol.The desulfurization rate of dibenzothiophene was 94.13%,under the conditions of water/oil ratio 1∶1,100min,45℃,with hydrogen peroxide/formic acid as the oxidant and TBSB as the phase transfer catalyst.From the kinetics' study,it was shown that the reaction was pseudo first-order reaction with rate constants of k₄₅℃=0.63 h^-1 and the activation energy Ea=18.02 kJ/mol.The desulfurization rate of gasoline was 92.56%,under the conditions of water/oil ratio 1∶1,120min,45℃, with hydrogen peroxide/formic acid as the oxidant and TBAB as the phase transfer catalyst.From the kinetics' study,it was shown that the reaction was pseudo first-order reaction with rate constants of k₄₀℃=3.54 h^-1 and the activation energy Ea=59.39 kJ/mol.An insight study of the mechanism of oxidative desulfurizarion by phase transfer catalysts was also carried out and the cycling model and dynamic model were developed. There are two steps in the process of liquid-liquid phase system of oxidation of thiophene by phase transfer catalysts,containing the extractive equilibrium and the oxidative reaction.In the transfer process,there is a complexation[RCOOO—Q—X]formed.It could enhance the transfer rate and lower the apparent activation energy,thus the reaction was accelerated.