Abstract
SiO2-SO3H, with a surface area of 115 m2·g−1, pore volumes of 0.38 cm3·g−1 and 1.32 mmol H+/g, was used as a transesterification catalyst. Triglycerides of waste cooking oil reacted with methanol in refluxing toluene to yield mixtures of diglycerides, monoglycerides and fatty acid methyl esters (FAMEs) in the presence of 20% (w/w) catalyst/oil using the hydrophilic sulfonated silica (SiO2-SO3H) catalyst alone or with the addition of 10% (w/w) co-catalyst/oil [(Bun4N)(BF4) or Aliquat 336]. The addition of the ammonium salts to the catalyst lead to a decrease in the amounts of diglycerides in the products, but the concentrations of monoglycerides increased. Mixtures of (Bun4N)(BF4)/catalyst were superior to catalyst alone or Aliquat 336/catalyst for promoting the production of mixtures with high concentrations of FAMEs. The same experiments were repeated using DMSO as the solvent. The use of the more polar solvent resulted in excellent conversion of the triglycerides to FAME esters with all three-catalyst media. A simplified mechanism is presented to account for the experimental results.
Highlights
According to the definition provided by the American Society for Testing and Materials (ASTM), fatty acid methyl(ethyl) esters is a fuel consisting of “long chain fatty acids of mono-alkyl esters derived from renewable fatty raw material such as animal fats or vegetable oils” [1]
It was reported by some researchers that homogeneous base catalysts are only effective for the fatty acid methyl esters (FAMEs) production via the transesterification process using the feedstocks with an free fatty acid (FFA) content of less than 2 wt% [2]
The soap inhibits the separation of FAME and glycerin, and the water can hydrolyze the esters in a reaction that competes with the transesterification
Summary
According to the definition provided by the American Society for Testing and Materials (ASTM), fatty acid methyl(ethyl) esters (biodiesel) is a fuel consisting of “long chain fatty acids of mono-alkyl esters derived from renewable fatty raw material such as animal fats or vegetable oils” [1]. Gonçalves et al [8] utilized a heterogeneous magnetic acid catalyst MoO3/SrFe2O4 composed of molybdenum oxide (MoO3) supported on strontium ferrite (SrFe2O4) to Molecules 2022, 27, 953 catalyze the transesterification of waste cooking oil They obtained 95.4% conversion into esters at 164 ◦C using a 40:1 molar ratio of alcohol-to-oil, 10% catalyst and a reaction time of 4 h. There is a need for acid pre-treatment of such low-quality feedstocks to reduce FFA content to a bearable amount prior to base-catalytic transesterification to use high FFA feedstocks in a single-run process [12] These limitations in the use of heterogeneous basic catalysts for biodiesel production are the principal driving forces for the development of new catalytic systems for biodiesel synthesis that are easier to manage and reuse.
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