Valorization of acidic waste oils through conversion to biodiesel catalysed by an acidic ionic liquid
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abstract
Biodiesel is an alternative diesel fuel which is industrially produced from vegetable oils and animal fats. Currently most commercial biodiesel is produced from oils, using alkaline catalysts. However, conventional mineral acid catalysts like sulfuric acid, are commonly used to catalyze esterification reactions of fatty acids which also produce biodiesel. Ionic Liquids (ILs) offer an alternative solution to classical homogeneous catalysts, because it can be recycled and reused in subsequent runs after a few recovery steps. In this study, a Brønsted acidic IL, 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4) was used as a catalyst in the conversion of a simulated acidic waste oil, based in mixtures of a waste cooking oil and oleic acid, into biodiesel by esterification/ transesterification reactions. The kinetic studies showed that the esterification reaction can be modeled as a third order reaction with an activation energy of 52.2 kJ/mol, and was significantly influenced by the temperature and molar ratio of oil/alcohol. The methodology proposed for recovery of the IL is adequate because it has the capacity to recover the IL with high purity. After five reaction/recovery cycles, the conversion efficiency falls from 93.4% to 86.9% and the FAME content decreases from 18.4%wt to 11.5%wt. The IL [BMIM]HSO4 was not able to promote the transesterification reaction of the simulated oil but presented promising results for the esterification reaction and for a treatment of oils with high acidity.
