Synthesis Of Ionic Liquids And Their Application To Alkylation Desulfurization Of FCC Gasoline

Along with the increasing global awareness of environmental protection, the production of low-sulfur or sulfur-free gasoline has became the general trend of the world’s clean energy. Thiophenic sulfurs are the main sulfide in gasoline, so the research of desulfurization methods aims at removing the thiophenic sulfurs. The conventional hydrodesulfurization method and the oxidation desulfurization method can effectively remove thiophenic sulfurs, but the hydrodesulfurization method has several disadvantages, namely harsh operating conditions, the need of hydrogen, serious loss of octane. The oxidation desulfurization method has the shortcomings of poor activity and selectivity of catalyst, security risk of the use of H2O2, difficult treatment of sulfur-containing wastewater. Thus the alkylation desulfurization method has became a hotpot in recent years, and the catalyst species of alkylation desulfurization are the ion exchange resin catalyst、zeolite catalyst、solid phosphoric acid catalyst and ionic liquid. By comparison, the operating conditions of ionic liquid are more moderate. On the one hand, the ionic liquid not only can be used as a solvent but also a catalyst in the alkylation reaction, on the other hand, the ionic liquid can be easily separated from the product, achievinge a truly green because of avoiding the use of polluted solvent system.Adopted one-step method, this paper respectively used Et3NHCl、[BMIM]Br as cationic and AlCl3、FeCl3 as anion to make ionic liquids. The alkylation desulfurization of FCC gasoline with ionic liquids was studied to evaluate the performance. The optimal synthetic conditions were carried out, the results showed that AlCl3 was the best anion. The optimum conditions of Et3NHCl-AlCl3 ionic liquid were as follows:the molar ratio of AlCl3 and Et3NHCl was 2.1:1, the reaction temperature was 80℃ and the reaction time was 3.5h. The optimum conditions of [BMIM]Br-AlCl3 ionic liquid were as follows:the molar ratio of AlCl3 and [BMIM]Br was 1.8:1, the reaction temperature was 60℃ and the reaction time was 3.5h. The spectrums of ironic liquids by Fourier Transform Infrared Spectroscopy appeared the O-H vibration, indicating the generation of Al(OH)3. The ironic liquids should be isolated from air to be stored on account of their water-sensitivity.The Et3NHCl-AlCl3 ionic liquid and [BMIM]Br-AlCl3 ionic liquid were used in FCC gasoline desulfurization by alkylation. When the mass ratio of Et3NHCl- AlCl3 ionic liquid to oil was 0.033:1, the reaction temperature was 60℃ and the reaction time was 65min, the sulfur content in FCC gasoline B reduced from 611.8μg/g to 145.6μg/g, the desulfurization rate was 76.20%, the mass yield was 87.68%. When the mass ratio of [BMIM]Br-AlCl3 ionic liquid to oil was 0.023:1, the reaction temperature was 70℃ and the reaction time was 70min, the sulfur content in FCC gasoline B reduced from 611.8μg/g to 46.7μg/g, which met the national gasoline sulfur content standard Ⅳ(<50μg/g), the desulfurization rate was 92.27%, the mass yield was 86.42%.The desulfurization effect of regenerated ionic liquids by extraction was worse than fresh ones. Therefore, further research about the regeneration of ionic liquid was needed.The engler distillation range、the sulfur distribution and the family component distribution of non-refined and refined oil were analyzed. The results of engler distillation range indicated that the alkyl-thiophenic sulfides with greater molecular weight and higher boiling point were generated after alkylation reaction. The results of the sulfur distribution found that Et3NHCl- AlCl3 ionic liquid could easily remove n-butyl mercaptan、thiophene mehyl--thiophene、C2-thiophene、C3-thiophene and C4-thiophene, [BMIM]Br-AlCl3 ionic liquid could easily remove t-butyl mercaptan、n-butyl mercapta、mehyl--thiophene and C2-thiophene. The results of family component distribution demonstrated that the content of n-paraffin、naphthene and aromtics increased and the content of i-paraffin and olefin decreased afer the desulfurization by two ionic liquids. The change of family component distribution illustrated the side reactions occurred when the alkylation reaction of olefin with sulfide in FCC gasoline. The two ionic liquids used in the desulfurization of FCC gasolines with different sulfur content showed well adaptability.By comparison, the cation of Et3NHCl- AlCl3 ionic liquid was inexpensive and easy to get, but the [BMIM]Br-AlCl3 ionic liquid had the advantage of less catalyst consumption and low sulfur content. The sulfur content of refined gasoline by [BMIM]Br-AlCl3 ionic liquid met the national gasoline sulfur content standard Ⅳ(<50μg/g). If a better regeneration method of used ionic liquids was found, the alkylation desulfurization with ionic liquid will have some industrial application.