Transesterification of cottonseed oil catalyzed by brønsted acidic ionic liquids

Transesterification of cottonseed oil with methanol to biodiesel was investigated in various Brønsted acidic ionic liquids with an alkane sulfonic acid group. The properties, structures, and acidities of the ionic liquids were experimentally characterized and theoretically analyzed. The Brønsted acidity - activity correlation for the ionic liquids was studied. Among all these ionic liquids, 1-(4-sulfonic acid) butylpyridinium hydrogen sulfate exhibited the best catalytic performance, which is ascribed to its strong Brønsted acidity. The catalytic activity of ionic liquids was near that of concentrated sulfuric acid. The influences of ionic liquid dosage, molar ratio of methanol to cottonseed oil, and reaction temperature were explored using 1-(4-sulfonic acid) butylpyridinium hydrogen sulfate as the catalyst; the results were systematically explained. A high yield of fatty acid methyl esters of 92% was obtained under a mild reaction condition. The separation of the biodiesel can be performed by simple decantation.