Ultrasound-assisted solid Lewis acid-catalyzed transesterification of lesquerella triglycerides for biodiesel synthesis



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Biodiesel research has attracted recent interest because of the depletion of fossil fuel reserves, environmental pollution, and global warming problems. Synthesized from vegetable oils and animal fats consisting of a mixture of fatty acid methyl esters (FAMEs), biodiesel is a potential alternative to mineral fuels. Many biodiesel synthesis pathways from different feedstocks have been reported since its first application in diesel engines by Rudolph Diesel in 1893. It is bio-renewable, non-toxic, and biodegradable. In order to reduce environmental pollution and ease dependance on non-renewable fuel sources, scientists must develop synthesis processes which are more technically viable, sustainable, and straightforward. This work aims to study the sonochemical transesterification of lesquerella triglycerides using solid Lewis acid catalysis. The oil is extracted sonochemically from a new feedstock involving Lesquerella fendleri seeds. The biproduct of oil production from the seeds (the mash) can be used as animal feed, making the crop completely bio-friendly. Besides castor oil, lesquerella oil is the only vegetable oil containing a hydroxy fatty acid (lesquerolic acid), which could, in addition to producing biofuel, could also generate chemically important cyclic lactones. AlCl3, SnCl2, and Sn(CH3COO)2 showed catalytic activity using direct immersion ultrasound among a list of Lewis acid catalysts investigated, with AlCl3 being the best catalyst. Ultrasound increased the rate of reaction by facilitating carbocation formation of glyceridic carbons. Experimental investigations were carried out at room temperature in a solvent volume range from 3:1 to 18:1 (methanol: oil) and catalyst loading from 1 wt.% to 6 wt.% over 10 to 60 min sonication time at 48% ultrasound amplitude. Complete conversion (>99%) was achieved in 40 min with 5 wt.% AlCl3 catalyst. The process parameters were optimized using a statistical regression analysis with STATA 14.0 software. The catalytic effect of CaO as a heterogeneous base catalyst was also investigated for biodiesel synthesis from lesquerella triglycerides. Chemical characterization of the compounds was performed with nuclear magnetic resonance (NMR) spectroscopy (1H NMR & 13C NMR), and % conversion of FAMEs was calculated from the 1H NMR spectra. The fatty acid profile was determined by GC-FID and GC-MS analysis. The synthesis of biodiesel was further confirmed by FT-IR spectroscopy. Thermogravimetric analysis (TGA) was performed to check the volatility difference between FAMEs and triglycerides under nitrogen atmosphere. Results indicate that this is a fast, green, energy-efficient, non-corrosive and industrially applicable method for biodiesel production from lesquerella triglycerides.

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Biodiesel, Lewis Acid, Ultrasound