Production of biodiesel from sewage sludge lipids was catalysed by six different Brønsted 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, [mimC4SO3H][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, [N666(C4SO3H)][SO3CF3]. The influence of different reaction variables on the biodiesel yield was studied using [mimC4SO3H][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, 7wt% ionic liquid catalyst (wt%, based on lipids), 100°C and 5h. 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.
- Ionic liquid
- Sewage sludge lipids