Biodiesel production from sewage sludge lipids catalysed by Bronsted acidic ionic liquids

Production of biodiesel from sewage sludge lipids was catalysed by six different Bronsted acidic imidazolium and long chain ammonium ionic liquids; both with an alkane sulfonic acid group and with different anions. Among the ionic liquid tested, 4-(3-methylimidazolium) butanesulfonic acid trifluoromethanesulfonate, [mimC(4)SO(3)H][SO3CF3], was selected as the best catalyst due to its high catalytic performance and purer biodiesel obtained than the equivalent ammonium ionic liquid, 4-(trihexylammonium) butanesulfonic acid trifluoromethanesulfonate, [N-666(C4SO3H)][SO3CF3]. The influence of different reaction variables on the biodiesel yield was studied using [mimC(4)SO(3)H][SO3CF3] as a catalyst. The yield of fatty acid methyl esters (biodiesel) reached 90% (based on saponifiable lipids) under the following optimised conditions: 10:1 molar ratio of methanol to saponifiable lipids, 7 wt% ionic liquid catalyst (web, based on lipids), 100 degrees C and 5 h. In addition, the ionic liquid has a good reusability and can be easily separated from the biodiesel. These acidic ionic liquids were found to be efficient catalysts for the synthesis of biodiesel from low-cost and non-edible feedstock like sewage sludge lipids. (C) 2015 Elsevier B.V. All rights reserved.