Preparation of supported acidic ionic liquid by covalent bond grafting and its catalysis in synthesis of n-butyl acetate

Immobilized acidic ionic liquid catalyst [(CH₂)₃ SO₃HVIm]HSO₄/silica gel was prepared from 1-vinylimidazole (VIm) acidic ionic liquid and 3-mercaptopropyltrimethoxysilane modified silica gel by radical polymerization with azodiisobutyronitrile as initiator. The method is so called covalent bond grafting. The catalyst was characterized by means of FTIR, TG-DSC and element analysis. Results showed that ionic liquid was well confined on modified silica gel. The catalyst is good in thermal stability. The supported capacity of [(CH₂)₃SO₃HVIm]HSO₄ on modified silica gel is 2.671 mmol/g(based on 1 g catalyst). The catalyst was used in synthesis of n-butyl acetate by esterification of acetic acid with n-butyl alcohol. Under optimal esterification conditions: temperature 94°C, mole ratio of n-butanol to acetic acid 1.2, mass ratio of catalyst to reactants 0.06 and reaction time 3 h, the yield of n-butyl acetate can reach 99.5%. The catalyst can be separated easily and yield of n-butyl acetate can maintain at 90.1% after reuse for 8 times.