Synthesis of strong acid polymeric ionic liquids and their catalysis of esterification

Three kinds of acid polymeric ionic liquids (ILs) were prepared by a two-step method. The characterization results showed that the decomposition temperature was above 200℃. Both anion structures and the side chain length had effects on the activity of ILs. IL3 ([(CH₂)₄SO₃HVIm]HSO₄) was chosen to be immobilized on the modified attapulgite (ATP) for preparation of heterogeneous catalysts. The esterification reaction between oleic acid and methanol was selected to test the catalyst activity. When the reaction temperature was 65℃, molar ratio of methanol to oleic acid 6:1, and dosage of catalyst 0.7 g [the immobilization rate 36%(ω)], the yield of methyl oleate reached over 58% after 5 h. After 4 reusing cycles of the ATP-PIL, the yield of methyl oleate was still above 33%. Moreover, the catalyst could be easily separated and recycled.