Catalytic synthesis of n-butyl carboxylate with immobilized ionic liquid based on response surface methodology optimization

Abstract

Four kinds of functional ionic liquids (ILs) ([C₃SO₃Hnmp]HSO₄), 1-(3-sulfopropyl)-1-methylpyrrolidone phosphate ([C₃SO₃Hnmp]H₂PO₄), 1-(3-sulfopropyl)-1-methylpyrrolidone p-toluene sulfonate ([C₃SO₃Hnmp]CH₃SO₃H) and 1-(3-sulfopropyl)-1-methylpyrrolidone methyl sulfonate ([C₃SO₃Hnmp]C₆H₆SO₃H)) were prepared and the catalytic activity of these ILs during esterification of carboxylic acids (formic acid, acetic acid, propionic acid, butyric acid) with alcohols was investigated. The results indicated that the IL ([C₃SO₃Hnmp]HSO₄) exhibited an optimal catalytic performance. And then the IL ([C₃SO₃Hnmp]HSO₄) was immobilized to the silica gel. The immobilized IL performed more excellent catalytic activity than the unsupported [C₃SO₃Hnmp]HSO₄. The effects of reaction temperature, reaction time, molar ratio of acid to alcohol and catalyst dosage were investigated. The response surface methodology based on the Box-Behnken design (BBD) was used to explore the best reaction condition of different experimental variables. Accordingly, a high n-butyl butyrate yield of 97.10% under the deduced optimal reaction conditions was obtained, in good agreement with experimental results and that predicted by the BBD model. The immobilized IL [C₃SO₃Hnmp]HSO₄ maintained high catalytic activity after five cycles.

Keywords: esterification; immobilized; ionic liquid; response surface.