Abstract
Nowadays, biodiesel has become a very promising alternative to fossil diesel fuel, regarding environmental concerns and fuel resource depletion. Biodiesel is usually produced through homogeneous or heterogeneous transesterification of different fatty raw materials. Although main research has been carried out with homogenous catalysts, heterogeneous catalysts may be of interest due to ease of recovery and recycling, as well as readiness for continuous processing. In this work, calcined Mg-Al hydrotalcite (HT) was used for the heterogeneous transesterification of waste cooking oil. Three reaction parameters, namely, reaction time, amount of catalyst, and methanol-to-oil molar ratio, were optimized by means of Response Surface Methodology (RSM) at constant temperature (65 °C), using a Box-Behnken design. Optimal fatty acid methyl ester (FAME) content (86.23% w/w FAME/sample) was predicted by the model with an R-squared value of 98.45%, using 3.39 g of HT (8.5% w/w oil) and an 8:1 methanol-oil molar ratio, for a duration of 3.12 h. It was observed that calcination of HT, while avoiding the previous washing step, allowed the presence of chemical species that enhanced the effect of the catalyst. It can be concluded from this field trial that calcined and nonwashed Mg-Al hydrotalcite may be considered an effective basic catalyst for the production of biodiesel from waste cooking oil. Also, RSM proved to be a useful tool for predicting biodiesel yield.
Highlights
Environmental concerns about global warming and climate change have greatly increased the interest in renewable fuels for internal combustion engines
It was observed that calcination of HT, while avoiding the previous washing step, allowed the presence of chemical species that enhanced the effect of the catalyst. It can be concluded from this field trial that calcined and nonwashed Mg-Al hydrotalcite may be considered an effective basic catalyst for the production of biodiesel from waste cooking oil
Mainly CaO, are the most studied solid catalysts, as they show high basicity, low miscibility in methanol, and the fact that they can be synthesized from low-cost sources [8,10,11]
Summary
Environmental concerns about global warming and climate change have greatly increased the interest in renewable fuels for internal combustion engines. Provided that the higher the raw material acidity, the smaller the conversion efficiency [3], different strategies have been proposed, i.e., the use of solid catalysts for biodiesel production—basic zeolites, alkaline earth metal oxides, and hydrotalcites (HT) among them [7,8,9]. Mainly CaO, are the most studied solid catalysts, as they show high basicity, low miscibility in methanol, and the fact that they can be synthesized from low-cost sources [8,10,11] With this catalyst activated by ultrasound, Verziu et al [12] achieved 97% conversion, at 348 K, with a methanol-to-oil molar ratio of 4:1. The search of an efficient catalyst to convert a wide range of raw materials into biofuel may help to develop an economically biodiesel production method
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