Optimization of reaction conditions for biodiesel synthesis from a waste cooking oil using [HMIM]HSO4 ionic liquid as catalyst

The objective of this work is to study the influence of applying 1-methylimidazolium hydrogen sulfate [HMIM]HSO4 ionic liquid on the catalysis of esterification/transesterification reactions of an acidic waste cooking oil (WCO). Samples of simulated oils with variable acidity were used as raw material. The samples were prepared by the incorporation of diverse contents of oleic acid in a qualitatively and quantitatively characterized WCO. An experimental design based on a total factorial was generated with three parameters at two levels (23) in duplicate: A - incorporated oleic acid (%wt.), B - methanol/ simulated oil molar ratio, and C - reaction time. Two responses were evaluated: the reaction conversion of the simulated oil, measured according to the procedure described in the European Standard EN14104/2008, and the produced biodiesel FAME content, estimated by GC-FID, according to the procedure established in the European Standard EN 14103/2003. The fixed reaction parameters were: temperature, 90°C, and catalyst charge, 10% wt, and the statistical analysis was carried out with Design Expert 11 software. The influence of the factors for the conversion response was C>B>A, and the optimal conditions were: 20% (A), 1:40 (B), and 8h (C), reaching a maximum conversion of 96.6%. On the other hand, regarding the FAME content response, the influence of factors was A>C>B, and the optimal conditions were, 40% (A), 1:20 (B), and 8h (C), for a maximum FAME content of 36.5%. It is concluded that the studied IL promoted mainly the esterification of the free fatty acids in the WCO samples, and apparently had little influence in promoting transesterification reactions.