Noncorrosive Ionic Liquids Composed Of "HSO₄" As Esterification Catalysts

Esters are important intermediates in chemical and pharmaceutical industries, and they are mostly produced by acid-catalyzed esterification reactions. Various mineral acids, such as H2SO4, HF, and H3PO4 have been widely used as catalysts in the production of esters. However, these acids are extremely corrosive and contaminative, leading to the difficulties in separating and recycling these catalysts. They must have to be neutralized at the end of the reaction. To overcome the above mentioned problems, the use of heterogeneous catalysts such as resins, heteropolyacids, and molecular sieves has attracted much attention. However, these catalysts also have their disadvantages such as easy deactivation, high mass transfer resistance, and especially difficult installation in a reactive distillation column, which limits their practical applications. Therefore, green catalyst of high catalytic activity is also of important significance and highly conceived for the esterificaiton reaction.Br(?)nsted acidic ionic liquids (BAILs), regarded as green reaction media, have been introduced very successfully into the area of catalysts. Acid-catalyzed esterification reactions based on ionic liquids have received more attention. In this paper, four BAILs were synthesized and characterized. The esterification reactions were studied in the presence of those BAILs, and the kinetics of esterification of acetic acid with n-butanol was also investigated in detail. The experimental results show that the optimized reaction conditions are as follows:reaction temperature 100℃, catalyst loading 25% w/w, the molar ration of acid to alcohol 2:1. In addition, it is also demonstrated that the PH model can give a good representation of the esterification kinetic behavior at a low catalyst loading. The catalytic activities are mainly influenced by the preexponential factors of forward reaction, when the reaction energy barriers (activation energy) are quite similar.