Production and characterization of biodiesel catalysed by 1-butyl-3-methylimidazolium hydrogen sulfate

Abstract

Biodiesel is a fuel generated from renewable resources with the ability to replace diesel in combustion engines. In the current scenario, its production is carried out through the esterification of free fatty acids (FFA) or the transesterification of triglycerides, always associated to catalysts, being acidic and basic respectively. The present study evaluates the influence of the application of 1-butyl-3-methylimidazolium hydrogen sulphate ionic liquid (IL), [BMIM]HSO4, in the catalysis of the transesterification reaction of a simulated oil by the incorporation of oleic acid (OA) into the waste cooking oil in proportions of 20 and 40%wt. The operation parameters of oil/methanol molar ratio (1:20 and 1:40 mol/mol) and reaction time (4 and 8h) were studied by applying a Response Surface Methodology (RSM) using an experimental planning of Total Factorial 23, with the conversion of the simulated oil and the FAME content in the produced biodiesel being selected as the responses for this analysis. It is concluded that the factors of greater influence in the production of biodiesel were the incorporation of OA and the reaction time for both responses. Using a fixed catalyst load of 10%wt and a reaction temperature of 65 °C, optimum conditions for conversion were determined to be 20%wt OA incorporation, 1:20 oil/MeOH molar ratio and reaction time of 8h, leading to a conversion of 87.8%. For the FAME content the optimum condition was estimated at 40%wt OA incorporation, oil/MeOH molar ratio of 1:20 and reaction time of 8h, with a FAME content response of 37.6%wt. The optimum condition for both responses was determined through the RSM, and it is characterized by 37.3%wt OA incorporation, oil/MeOH molar ratio of 1:20 and reaction time of 8h, leading to a conversion of 82.2% and a FAME content of 35.6%wt. The kinetic studies showed that the esterification reaction of oleic acid can be modeled as a third order reaction with activation energy of 52.2 kJ/mol, and was significantly influenced by the temperature and molar ratio of oil/alcohol. It was possible to determine that with an oil/MeOH molar ratio of 1:25 the reaction reaches its optimum and that increasing the temperature the reaction conversion increases. The methodology of recovery of the ionic liquid proposed 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. In conclusion, the ionic liquid [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.