Study On The C₄ Alkylation Reaction Catalyzed By Ionic Liquid/Solid Acid Catalysts

In the petrochemical industry,the alkylation of isobutane and butenes is an important process to produce high octane gasoline.Sulfuric acid and hydrofluoric acid are the two conventional catalysts for C₄ alkylation reaction.However,many drawbacks of conventional catalysts limited the commercial application of C₄alkylation.With the increasing awareness of environmental protection,many researchers are looking for more moderate and“green”alkylation catalysts to alternate conventional liquid acids.Solid acids and ionic liquids are new catalytic materials that have been paying attention to by the researchers.Solid acids have many favorable properties for the C₄ alkylation.Most solid acids are non-halogen catalysts,and then the solid acid alkylation is an environmentally friendly catalytic process with lower corrosive.Meanwhile,the catalyst and the product are easy to be separated.However,solid acids also have many shortcomings.Insufficient acidity of a solid acid always makes it difficult to catalyze the alkylation reaction efficiently.Olefin oligomers easy to be produced in the solid acid alkylation,which would block the pores of the catalyst,cover the acidic sites,and make the catalyst deactivate quickly.Ionic liquids can provide more acidity in the alkylation reaction,and can continuously catalyze the alkylation.Besides,ionic liquids could improve the selectivity of desired products by increasing the absorption ability of butenes.However,ionic liquids have many obvious shortcomings:the acid consumption of ionic liquids is usually as large as the inorganic acids;most of ionic liquids are sensitive to moisture;halide ions of the ionic liquids tend to be accumulated in alkylates,causing the problem of corrosion;the ionic liquids are difficult to be regenerated in the end of alkylation reaction.It is found that solid acids and ionic liquids are complementary modalities for C₄ alkylation.In this paper,we mainly focus on loading ionic liquid onto solid acids,which may be combined the advantages of two catalysts.Firstly,we compared the product distribution before and after loading liquid acids on MCM-41 molecular sieves to investigate the alkylation performance of new catalyst system.The transition metal compounds were introduced into the liquid acids to improve the catalytic selectivity.The results show that Cu Cl obviously influence the catalytic performance of MTBE-AlCl₃ supporting molecular sieve.Secondly,transition metals were also introduced on the supporter to modify the solid acids.When the ionic liquid MTBE-AlCl₃ support the Zn Cl₂ modified solid acid,the novel catalysts have the best alkylation performance.Thirdly,by means of the characterization for the new catalytic system,the mechanism of the alkylation of solid acid/ionic liquid was analyzed.It is found that the acidity play an important role on the alkylation performance of the novel catalyst.In summary,we studied the catalytic performance of solid acid/ionic liquid system.The combination of solid acids and ionic liquids maybe provides a new way for improving the performance of the present commercial alkylation,and then promote the development of C₄ alkylation.