(576f) Transesterification Rates for Acid Catalyzed Methanolysis of Model Glycerides

Biodiesel is a renewable fuel produced from vegetable oils and animal fats via the transesterification reaction. The raw material is converted to fatty acid alkyl esters after reaction with alcohol and a base, or alcohol and an acid. Most of the current literature focuses on base-catalyzed transesterification kinetics, which is the preferred conversion method for feedstocks with low free fatty acid content. This paper will present the kinetics of model acyl glycerides and free fatty acids using acid catalyzed transesterification. The rate information could be applied to produce biodiesel from high free fatty acid feedstocks, such as rendered fats, soapstocks, and microbial oils. The rate constants for conversion of several palmitic acid glyceryl esters to fatty acid methyl esters were determined at 60 °C, with initial concentrations of 1.5 mM in 0.1% sulfuric acid in methanol. The rate constants were determined by following the appearance of methyl esters by GC/FID. All determinations were made in homogeneous solutions. The least soluble of these compounds was tripalmitin. The selected concentration for the experiments (1.5 mM) was just above the solubility limit for this compound at 60 °C in methanol. Rate data for tripalmitin, 1,2-dipalmitin, 1,3-dipalmitin, and 1-monopalmitin were obtained and compared with rates for tristearin, and triolein, which were obtained individually and by competitive rate experiments.