Application Of Deep Eutectic Solvent In Oxidative Desulfurization Process

Sulfide produced by oil burning is the main source of air pollution,and also seriously endangers human health.In the current national VI gasoline standard,the sulfur content of oil is required to be less than 10 ppm.At present,the main desulfurization process of domestic refineries is hydrodesulfurization,but HDS can only achieve deep desulfurization of oil under harsh reaction conditions.The oxidation desulfurization system with deep eutectic solvent as extractant and oxidant can keep a high removal rate of thiophene sulfide under mild reaction conditions,so as to achieve deep desulfurization of oil products.In this paper,three kinds of deep eutectic solvents were synthesized by heating and stirring and used in oxidative desulfurization experiments.（1）Using caprolactam as hydrogen bond acceptor and lactic acid as hydrogen bond donor,lactic acid based deep eutectic solvent was synthesized.The hydrogen bond interaction between caprolactam and lactic acid was determined by FT-IR and ~1H NMR.Using dibenzothiophene and n-octane as raw material,lactic acid based deep eutectic solvent as extractant and cocatalyst,hydrogen peroxide as oxidant and ammonium molybdate as catalyst,the effects of reaction temperature,n（H₂O₂）/n（DBT）,amount of catalyst added,V(C₆H₁₁NO/C₃H₆O₃)/V（oil）and sulfide type on the desulfurization rate of the simulated oil were investigated,The optimum reaction conditions were determined as follows:reaction temperature 70℃,reaction time 100 min,n（H₂O₂）/n（DBT）is 6:1,the mass concentration of ammonium molybdate is 4 mg/m L and V(C₆H₁₁NO/C₃H₆O₃)/V（oil）is 1:10.Under the optimal reaction conditions,the desulfurization rates of the simulated oil,4,6-dimethyldibenzothiophene and benzothiophene were100%,98%and 78%,respectively.After using for 5 times,the desulfurization rate of lactic acid based deep eutectic solvent can still reach95%,which has good reusability.（2）Phenol type deep eutectic solvent was synthesized by using choline chloride as hydrogen bond acceptor and phenol as hydrogen bond donor.The structure of dibenzothiophene in the simulated oil was determined by FTIR and ~1H NMR.Phenol type deep eutectic solvent was used as extractant,hydrogen peroxide as oxidant and titanium sulfate as catalyst.The effects of reaction temperature,V（Ch Cl/2Ph）/V（oi L）,n（H₂O₂）/n（DBT）,catalyst dosage and sulfide type on desulfurization efficiency were investigated.The results show that the desulfurization rate reaches 98.2%under the optimum reaction conditions,V（Ch Cl/2Ph）/V（oi L）is 1:5,n（H₂O₂）/n（DBT）is 6,the catalyst dosage is 0.01 g,the reaction temperature is 40℃,and the reaction time is 180 min.The apparent activation energy is 41.9 KJ/mol.The activity of phenol type deep eutectic solvent did not decrease obviously after 5 times reuse.The mechanism of extraction oxidation desulfurization was studied.The results show that the formation of Ti peroxide and sulfuric acid is the key to high desulfurization activity.（3）Citric acid type deep eutectic solvent was synthesized by heating choline chloride and citric acid.The extraction oxidation desulfurization system was formed with citric acid deep eutectic solvent as extractant and potassium bisulfate solution as oxidant.The FTIR and ~1H NMR show that the structure of deep eutectic solvent is stable and hydrogen bond has been formed.The effects of reaction temperature,different ratio of eutectic solvent,amount of water and oxidant on desulfurization rate were investigated.The results show that when the ratio of deep eutectic solvent is 2:1,the reaction temperature is 30℃ and the reaction time is 2 hours,1 m L citric acid type deep eutectic solvent is used for extraction for 0.5 h,and then 0.6 g potassium bisulfate solution is added for oxidation reaction,the removal rate of dibenzothiophene can reach 98.8%,and the removal rates of 4,6-dimethyldibenzothiophene and thiophene are 98%and 32%respectively.The apparent activation energy of the reaction is 56.5 KJ/mol.The activity of citric acid type deep eutectic solvent did not decrease obviously after 5times recycling.