Waste oils valorization through biodiesel synthesis using [HMIM]HSO4 ionic liquid as catalyst
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Historically, economic growth was always dependent on energy generation, causing pressure on fossil energy sources. In this context, alternative renewable energy sources have been extensively studied. Hence, biodiesel, a biofuel obtained from renewable biomass for internal combustion engines or energy generation, exhibits potential to replace partially or totally fossil fuels. Biodiesel is chemically composed of FAME (fatty acid methyl esters), that can be obtained from the chemical reaction of triglycerides with an alcohol, in the presence of a catalyst. Different raw materials can be used to produce biodiesel, such as edible vegetable oils (soybean oil, rapeseed oil) or inedible oils (jatropha oil, castor oil), animal fats, waste cooking oils and oils extracted from algae. Acid and basic catalysts are applied to increase the reaction rate. For transesterification reactions, basic catalysts (NaOH or KOH) are the most commonly used. Alternative options for these catalysts are ionic liquids (ILs), which are being studied since they enable a more environmentally sustainable biodiesel production process. Such compounds have potential for recyclability, high catalytic activity, simple operating conditions and high conversion rates with short reaction times.
The objective of this work is to study the influence of applying 1-methylimidazolium hydrogen sulfate [HMIM]HSO4 IL on the catalysis of esterification/transesterification reactions of a highly acidic waste vegetable oil (WVO), in order to assess the viability of the use of acidic imidazolium based ILs as catalysts in biodiesel production processes. Therefore, samples of simulated oils with variable acidity were used as raw material. These samples were prepared by the incorporation of different contents of oleic acid (tech. 90%) in a previously qualitatively and quantitatively characterized WVO. For the reaction, methanol was used and IL [HMIM]HSO4 was applied as the catalyst. An experimental design based on a total factorial was generated with three parameters at two levels (2^3) in duplicate: incorporated oleic acid, methanol/simulated oil molar ratio, and reaction time. Two responses were evaluated: the 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.
