Research On Oxidative Desulfurization Of Sulfur Compounds In Fuel Oil With Molecular Oxygen

This work explored to oxidize the sulfur compounds in model fuel oil using oxygen as an oxidant.Firstly,in the absence of the catalysts system,octane reacted with oxygen to produce hydroperoxides in-situ,which were then used as oxidants to oxidize the sulfur compounds.The results indicated that the hydroperoxides generated in-situ were effective in oxidizing dibenzothiophene(DBT)to its corresponding dibenzothiophene sulfone(DBTO2).The influences of reaction temperature,reaction time,initial oxygen partial pressure on oxidative desulfurization were investigated,respectively.The removal of DBT could reach to 98.4%at 140?,4 h,at initial oxygen partial pressure 0.4 MPa.The influences of different hydrocarbon components in diesel oil on DBT removal were investigated.The oxidation mechanism was proposed and the concentration of hydroperoxides in both O2-oxidized octane and model diesel oil were detected.In addition,the optimal reaction conditions to oxidize thiophene(Th)were investigated.The removal of thiophene can reached to 81.8%at 150?,4 h,at oxygen partial pressure 0.8 MPa,V(Water)/V(Oil)=3:1.To decrease reaction temperature and reduce by-products,a series of H3+xPVxMo12-xO40(x=1-3)catalysts were prepared and screened for catalytic oxidation of DBT with O2 as oxidant.Based on the conversion of DBT,H5PMo10V2O40 showed the highest oxidative desulfurization activity.The catalysts were characterized by FT-IR,X-ray diffraction,TG and UV-Vis.The results demonstrated that H5PMo10V2O40 retained the Keggin structure of polyoxometalate and the V atom acted as the active centre.In the reaction the H5PMo10V2O40 catalyst reacted with oxygen to generate superoxide free radical then which reacted with H5PMo10V2O40 to produce reactive oxovanadate species.Then the reactive oxovanadate species oxidized dibenzothiophene to corresponding dibenzothiophene sulfone.A detailed parametric study was performed varying reaction temperature,reaction time,initial oxygen partial pressure,catalyst amount and sulfur species,to investigate their effects on desulfurization.Under 0.1 g catalyst amount DBT and 4,6-dimethyldibenzothiophene could be almost completely removed at 125? in 4 h and 0.3 MPa initial oxygen partial pressure.However,due to the effect of electron density the removal rate of benzothiophene only reached 60%under the same reaction conditions.The effects of different hydrocarbon components on DBT removal were studied.The addition of n-dodecane had no effect on the removal of DBT,but the cyclohexane and xylene had obvious influence.