Triglycerides with methanol

Biodiesel is a fuel derived from renewable natural resources such as soybean and rapeseed and consists of alkyl esters derived from transesterification of triglycerides with methanol. In spite of all the advantages of biodiesel, such as low emissiotts, biodegradability, non-toxicity, and lubricity, the major hurdle in penetration of biodiesel is its high cost because of the expensive food grade refined vegetable oil feedstock. 

Attention is drawn to the hazards involved in the use of perchloric acid in a published method [1] for transesterification of triglycerides with methanol. Alternative acid catalysts and safety precautions are suggested [2],... 

The transesterification of triglycerides with methanol is a simple and straightforward process. It is commercially practiced worldwide in the production of FAMEs, which have become popular as a replacement for diesel known as biodiesel . The process consists of three separate equilibrium reactions that can be catalyzed by both acids and bases. (4) The overall process is described in Figure 3. Phase separation of the glycerin is the predominant driving force for this process. 

In homogeneous catalysis, the catalyst is in the same phase as the reactants and products. Here we will concentrate on homogeneous catalysis in the liquid phase. In the classic case, the reactant (also called the substrate) molecules and the catalyst are reacted in a solvent. For example, the transesterification of fatty acid triglycerides with methanol (Figure 1.10) is catalyzed by hydroxide (OH-) ions. This is an important process for making fatty acid methyl esters which are then used as biodiesel. 

Figure 5.1. Alcoholysis of triglyceride with methanol, (a) overall reaction (b) three consecutive and reversible reactions. TG triglyceride DG diglyceride MG monoglyceride GL glycerol.

Fatty alcohols are mainly obtained by the reduction of the carboxylic function of natural triglycerides which are the essential components of animal or vegetal oils and fats ) They are produced by transesterification of triglycerides with methanol, followed by hydrogenolysis of the esters. 

Helwani, Z., Othman, M.R., Aziz, N., Kim, J., and Fernando, W. J.N. Solid heterogeneous catalysts for transesterification of triglycerides with methanol A review. Applied CatalA General 363,1-10 (2009). 

Fixed bed processes can be used for the l drogenation of fatty acid methyl esters. The methyl esters can be prepared direcdy from the fatty acid or by tra 5 -esterification of the triglyceride with methanol. The hydrogenation is carried out in a bed of solid copper chromite catalyst, which usually loses activity after operating for 3-6 months. Copper oxide/zinc oxide catalysts have also been used. 

The reaction of triglycerides with methanol proceeds in a stepwise manner to produce the intermediates of diglyceride and monoglyceride, with subsequent reactions with methanol producing glycerol and biodiesel. 

Biodiesel is a mixture of fatty acid methyl esters (FAMEs) which are produced from a broad range of crude oil materials, such as vegetable oil, animal fats, and waste oil, via transesterification of triglycerides with methanol or ethanol. Biodiesel has been regarded as a promising fuel to be able to partly substitute for conventional fossil diesel since it is obtained from renewable sources and for their environmental friendly properties like biodegradability and very low toxicity, lower perticulate emissions and increased lubricity and provides a means to recycle CO2 (Kim Dale, 2005, Ryan et al., 2006). 

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