The Comparative Study On Extraction And Catalytic Oxidation Of Dibenzothiophene From Oil

With increasing application of gasoline in the transportation, the sulfur compounds in gasoline can be inevitably converted to sulfur oxide(SOx) and airborne particulate emissions which lead to serious environmental pollution. As sulfur-containing compounds difficult to be removed, thiophenes are both an emphasis and a nodus in desulfurization. In this paper, dibenzothiophene(DBT) was selected as the target compound, and extractive desulfurization(EDS) and oxidative desulfurization(ODS) were selected for the research.Firstly, the performance of extractive desulfurization from gasoline was studied using a mixed solvent, which consisted of N,N-dimethylacetamide(DMAC), N,N-dimethylformamide(DMF) and tetramethylenesulfone(TMS). The effects of relevant parameters on EDS including volume ratio of DMAC/DMF/TMS, extraction temperature, extraction time, stirring speed, volume ratio of extractant and gasoline and extraction times were investigated, and the optimum extraction conditions were determined. The extraction removal of dibenzothiophene(DBT) and the residual sulfur content reached 99.1% and 9.5 mg?kg-1, respectively, at an optimal extractive condition of volume ratio of DMAC/DMF/TMS of 3:1:1 and volume ratio of extractant to gasoline of 1:5 at a stirring speed of 100 rpm over 10 min for extraction at 30oC(ambient temperature) with five extraction stages. The DMAC/DMF/TMS was reused three cycles and spent DMAC/DMF/TMS was rege nerated by adsorption method. Regenerated extractant could effectively extract DBT from fresh model gasoline with extraction effciency of nearly 90%.Secondly, the performance of catalytic oxidative desulfurization was studied using catalyst Mo O3/4A which was prepared by depositing molybdenum on 4A molecular sieve, a microporous material. The catalyst Mo O3/4A was characterized by the scanning electron microscopy(SEM), Fourier Transform Infrared Spectroscopy(FTIR) and X-ray photoelectron spectrum(XPS), and the data showed that molybdenum had been successfully immobilized on 4A molecular sieve, and the active site was the highest oxidation state Mo O3. Using oil-soluble cyclohexanone peroxide(CYHPO) as an oxidant, the catalytic oxidative removal of DBT and the residual sulfur content reached 99% and 5 mg?kg-1, respectively, at an optimal catalytic condition of molar ratio of CYHPO/DBT of 2.5 and volume mass ratio of model gasoline to catalyst Mo O3/4A of 100 at 100℃ over 30 min.Reaction kinetics of this experiment was simulated, and the results show that the catalytic oxidation of DBT and benzothiophene(BT) fitted the first-order kinetic model pretty well. The number of the catalyst used in repeated is an important index to measure the reliability of a catalyst. During the study, the total sulfur content of treated model gasoline no long met the EU fifth standard until the catalytic was reused for more than 4 times. Furthermore, the oxidation mechanism was examined.In conclusion, these two methods of desul furization were effective. However, the extractive desulfurization was better than catalytic oxidative desulfurization at the more moderate reaction condition, and the latter was superior to the former at fewer extraction times and the better regeneration performance. Through the study of these two desulfurization methods, the deep desulfurization in the laboratory was realized, which provided the theoretical reference for the industrial application.