Abstract
Replacing fossil fuels with biodiesel enables the emission of greenhouse gases to be decreased and reduces dependence on fossil fuels in countries with poor natural resources. Biodiesel can be produced by an esterification reaction between free fatty acids (FFAs) and methanol or by transesterification of triglycerides from oils. Both reactions require homogeneous or heterogeneous catalysis. Production of biodiesel catalyzed by heterogeneous catalysts seems to be the preferred route, enabling easy product separation. As we have previously shown, the Lewis acids AlCl3 and BF3 can serve as highly efficient catalysts under ultrasonic activation. The present study focused on the development of oleic acid (OA) esterification with methanol by the same catalysts immobilized in silica matrices using the sol–gel synthesis route. During the course of immobilization, AlCl3 converts to AlCl3 × 6H2O (aluminite) and BF3 is hydrolyzed with the production of B2O3. The immobilized catalysts can be reused or involved in a continuous process. The possibility of biodiesel production using immobilized catalysts under ultrasonic activation is shown for the conversion of FFAs into biodiesel in batch and continuous mode.
Highlights
Technological and demographic changes have caused an increase in the consumption of energy originating mainly from the combustion of fossil fuels, a nonrenewable natural resource, which has resulted in growing emissions of greenhouse gases [1,2]
In our previous publications we showed that BF3 and AlCl3 are effective catalysts in the esterification reaction between oleic acid (OA) and methanol [12] and in biodiesel production using brown grease as a source of free fatty acids (FFAs) [25]
Use of base catalysts was avoided at this stage to ensure acidic reaction conditions in the further esterification process. sol–gel matrices prepared via the one step procedure under acid catalysis usually have pore size in the micropore range [27]
Summary
Technological and demographic changes have caused an increase in the consumption of energy originating mainly from the combustion of fossil fuels, a nonrenewable natural resource, which has resulted in growing emissions of greenhouse gases [1,2]. The increased energy consumption has led to a search for alternative energy sources and prompted studies on renewable energy [3]. One of the most prominent economic alternatives to fossil oil is biodiesel, which is usually produced from the biomass of various crops. An increased use of crops for fuel production may lead to dilution of the world’s food sources [4,5]. The use of alternative sources for biodiesel production is being studied extensively [6]. World biodiesel production increased by 70% between 2005 and 2015 and is predicted to rise by another 35% by 2025
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