Boric Acid-based Ternary Deep Eutectic Solvents For Extraction And Oxidative Desulfurization Of Fuels

With the rapid development of industrial process,especially the increase of automobile use,the demand for natural resources such as petroleum fuel has increased dramatically.However,a large amount of SOx will be produced after combustion,which could have a negative impact on the environment and the safety of human life and property.In order to achieve the goal of sustainable development,the emission of sulfur compounds in fuel oil has been strictly controlled in various countries.At present,industrial desulfurization technology is hydrodesulfurization?HDS?,but it needs severe reaction conditions.Therefore,non-hydrodesulfurization has been highly sought after,especially the oxidative desulfurization?ODS?,which has some advantages including mild reaction conditions,easy to operate and high removal efficiency of polycyclic sulfide.As a new type of solvent,ionic liquids?ILs?have replaced flammable and volatile organic solvents in many fields.In recent years,they have been widely used in the desulfurization,but the synthesis steps are relatively complicated and difficult to degrade.In order to overcome these shortcomings,we have synthesized DESs,which is similar to ILs,have lower cost and more environmental protection than ILs.Boric acid was chosen as the hydrogen bond donor?HBD?.By adjusting the kinds of hydrogen bond acceptor?HBA?.A series of ternary borate based DESs was prepared and used as the extractants and catalysts for desulfurization reaction,and a new extraction coupled catalytic oxidation desulfurization system?ECODS?was established.Firstly,a series of ternary DESs were synthesized by one pot method with metal chlorides as HBAs,boric acid and polyethylene glycol as HBDs,used for desulfurization of model oil.The DESs were characterized by ¹H-NMR and FT-IR,which confirmed the hydrogen bond interaction between the components.Under the following conditions,T=60^oC,O/S=5,m_?DES?=2.5 g,V_?oil?=5mL,the DBT removal rate reached 98.7%,the desulfurization efficiency follewed the sequence of different sulfur-containing substrates:DBT>4-MDBT>4,6-DMDBT.According to the characteristics of ionic compounds and covalent compounds,the activity of ternary DESs was classified and investigated.The synergistic effect of Cl^-and boric acid was proved.In addition,the cycle stability of DES?ZnCl₂:BA:PEG?was also studied,and the reaction mechanism was proved that the active species was superoxide radical.Using choline chloride as HBA,ternary non-metallic borate based DESs were prepared with the same HBDs.The characterization of ¹H-NMR and FT-IR showed that the complex hydrogen bond formed between the components of DES seriously affected the signal of active hydrogen and the vibration of covalent bond in DES,which proved the successful synthesis of non-metallic DESs.Under the optimal conditions,the removal efficiency of DBT was got to 99.2%.After the reaction,DES could be regenerated and reused,and the catalytic activity of DES was almost not changed.The activity of model oils with different substrates were tested,which showed that steric hindrance inhibited the reaction obviously.Through ESR test,free radical capture experiment and DFT theoretical calculation,it was shown that O₂^·-free radical may be the main active oxygen species,and boric acid peroxide may also participate in the reaction system.The reaction product was also characterized and analyzed.Therefore,the mechanism was given based on the above discussion.In order to investigate the effect of DESs with different carbon chain lengths on desulfurization performance,the HBAs with different carbon chain lengths([C_n DMEA]Cl?n=1,4,8,12,16?were prepared,and boric acid and glycol were used as HBDs to prepare a series of ternary non-metallic borate based DESs with different carbon chain lengths C_n-DESs?n=1,4,8,12,16?,and a new ECODS was established.When T=65^oC and O/S=4,C₄-DES=1:3:5 as the research object,the deep desulfurization was achieved.The activity data showed that with the carbon chain length increased,the extraction activity gradually increased,which made the sulfide easily enter the DES phase.Thereby the performance of oxidative desulfurization could be improved.Furthermore,aromatics and alkenes were used as the disruptors.The results showed that alkenes in the system would form serious competitive reaction to DBT oxidation.ESR test and free radical capture experiment showed that superoxide radicals were produced in the reaction process.FT-IR showed that the product was DBTO₂.