Kinetics and phase behaviour of transesterification of triglycerides.
Published: 2006
Language: eng
Number of pages: 150
ISBN-13: 9780494217825
Description: Experiments were conducted to determine the optimum conditions for the transesterification of soybean oil using mixtures of methanol and ethanol. The optimum conditions found for the reaction were: (1) 50&deg;C, (2) 9:3:1 methanol/ethanol/oil molar ratio and (3) 0.5 wt% sodium methoxide catalyst.Two-phase base-catalyzed transesterification of vegetable oils is the most common method for making commercial biodiesel. During the transesterification, phase changes occur, which significantly affect the kinetics and steady state positions of the reaction.In addition, a new workup procedure was developed, in which oxalic acid in methanol was used to quench transesterification reactions. This avoided hydrolysis and converted all soap back to fatty acids.The removal of catalyst by the glycerol-rich phase, rapidly decelerated the reaction. At the beginning of the reaction the triglyceride, which entered the methanol phase was rapidly converted via diglyceride and monoglyceride to ester. Some triglyceride did not enter this methanol phase before the reaction decelerated, resulting in abnormally high level of triglyceride in the product. Glycerol separation also slowed down the soap formation in the biodiesel-rich phase, and removed the resulting soap into the glycerol-rich phase. Once the glycerol separated, mixing was required to re-suspend it and facilitate transfer of catalyst back to the ester phase.A polar dye was used to "visualize" phase behaviours in methanolysis, ethanolysis and butanolysis of soybean oil using a 6:1 alcohol oil molar ratio, 1.0 wt% catalyst (with respect to the oil) at ambient temperature. Methanolysis and ethanolysis reactions commenced as two phases (alcohol and oil), then formed emulsions and ended as two phases as glycerol byproduct separated. Butanolysis remained monophasic throughout. Ethanolysis was more easily initiated by mixing than was methanolysis. Ethanolysis also exhibited a much longer emulsion period and slower glycerol separation. The glycerol-rich phase was smaller in volume in ethanolysis than in methanolysis. At 23&deg;C, for methanolysis, 42.0% of the alcohol, 2.3% of the glycerol and 5.9% of the catalyst were in the ester-rich phase at steady state. In the ethanolysis, 75.4% of the ethanol, 19.3% of the glycerol and 7.5% of the catalyst were in the ester-rich phase.
Notes: Source: Dissertation Abstracts International, Volume: 68-01, Section: B, page: 0467.

Thesis (Ph.D.)--University of Toronto, 2006.

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