Catalyst-Free Oxidation Of Thiophenes In Crude Oil

Sulfur-containing compounds are common impurities in petroleum.During the combustion process of crude oil,pollutants such as sulfur oxides are generated,which have serious negative environmental impact.Thiophenes derivatives have always been very difficult to remove in traditional desulfurization processes.As people become more aware of environmental protection,the restrictions on the sulfur content in petroleum are also increasing.The effective removal of thiophene compounds from crude oil is a major problem in petroleum processing.Oxidative desulfurization is one of the most promising technologies for producing ultra-clean fuels.It can remove benzothiophene,dibenzothiophene and their derivatives that are difficult to remove by hydrodesulfurization.The conventional oxidative desulfurization requires the use of catalysts to promote the reaction.Based on this,we aim to find an effective method to oxidize thiophene compounds.In this research,we studied the oxidation of thiophene facilitated by ultrasound and continuous-flow reactor,and put forward new ideas and methods for the research of petroleum desulfurization.The specific research contents are as follows:(1)Oxidation of dibenzothiophene(DBT)under ultrasonic conditionsUltrasound can generate intensive energy,which can promote immiscible liquids to form emulsion thus to increase the interfacial area of a multiphasic reaction.This section focuses on the oxidation of dibenzothiophene(DBT)in the absence of a catalyst under ultrasonic conditions.First,two different ultrasonic generation methods were examined.It was found that the uses of high-power ultrasonic cleaner and ultrasonic cell crusher had little difference on the results of the oxidation reactions.Subsequently,the effects of oxidants and solvents were investigated.It was found that m CPBA and oxone afforded higher yields for the oxidation of DBT.Acetonitrile was found as the optimal solvent.In order to determine if the ultrasonic oxidation method can be applied in the desulfurization of real fuel,we used n-dodecane containing DBT as a simulant.Under these conditions,oxone was proved ineffective,while m CPBA gave the best results.(2)Oxidation of thiophenes under continuous-flow conditionsUnder microflow conditions,the oxidative desulfurization was simulated in dodecane.First,the oxidation of DBT were investigated under the established optimal conditions.The optimal reaction temperature was 60 oC,when m CPBA was used as the oxidant with DBT/m CPBA = 1:3(molar ratio).DBT was oxidized in flow with nearly quantitative yield,with a residence time of only 10 minutes.In order to verify the broad applicability of this method in the oxidative desulfurization of crude oil,we studied several other common thiophene impurities in fuels: benzothiophene(BT),2-methylbenzothiophene(2-MBT),3-methylbenzothiophene(3-MBT)and 4,6-dimethyldibenzothiophene(4,6-DMDBT).With residence times of 10 minutes,the isolated yields were 89%,92%,95%,and 95%,respectively.Gratifyingly,there results demonstrated promising advances of thiophene oxidation and oxidative desulfurization in continuous-flow.