Triglycerides biodiesel

The concentration of biodiesel (fetty acid methyl esters) and glycerides were analyzed by liquid chromatography (Shimadzu-lOA HPLC). An ODS-2 column (250x4.6mm) was used for the separation. The flow rate of the mobile phase (acetone acetonitrile=l l) was set to 1 ml/min. Peaks were identified by comparison with reference standards. Standards of methyl esters, monoglycerides, digjycerides and triglycerides were bought from Fluka. 

Considering the fact that the triglyceride oils used for the production of biodiesel are sulphur free, the use of biodiesel does not contribute towards the phenomenon of acid rain ... 

The peculiarity of this material is that it consists of a mixture of acids and not triglycerides therefore, its transformation in biodiesel requires only an esterification reaction instead of a irans -esterification one and therefore does not produce glycerol, making the total economy lighter and independent of the critical... 

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. 

Starch and fatty acids are the main food constituents of biomass. Sugar is derived from starch by hydrolysis or directly by extraction from sugar cane or beet. Fermentation converts sugars into alcohol that can be directly used as fuel, or in principle can be used as the raw material of a bioreftnery plant for further upgrading. Triglycerides, derived from oil seeds, are used to be converted into biodiesel through transesterification processes (Fig. 1.14). 

Keywords Triacetin, transesterification, glycerol, triglyceride, biodiesel... 

The standard analytical methods for biodiesel methyl ester are time-consuming and often require multiple physical analyzes per sample. NIRS allows for the simple set up of calibrations for multiple important biodiesel qualities such as mono-, di- and triglycerides, residual methanol, glycerol and moisture as well as... 

Most biodiesel is produced today through transesterification of triglycerides of refined edible oils (Scheme 10.1). 

The use of heterogeneous basic catalysts for the transesterification of triglycerides has long been considered the main tool to reduce processing costs in the production of biodiesel, as it would lead to simplified operations and eliminate waste streams. 

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. 

To produce biodiesel grade methyl esters, the oil must be trans-esterified with methyl alcohol. This process cleaves the triglyceride to yield glycerol and the individual methyl ester compounds. Most biodiesel trans-esterification is base catalyzed and has the operational advantage of low temperature, low pressure, and high conversion rates. 

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. 

Several processes for the production of biodiesel fuel have been developed by acid-, alkali-, and enzyme-catalyzed transesterification reactions (7-10). Transesterification, called alcoholysis, is the displacement of alcohol from an ester by another alcohol in a process similar to hydrolysis. Transesterification is represented by a number of consecutive and reversible reactions. The reaction step is the conversion of triglycerides to diglycerides, followed by the conversion of diglycerides to monoglycerides and of monoglycerides to glyceride at each step (11,12). 

Biodiesel fuel was prepared by a two-step reaction hydrolysis and methyl esterification. Hydrolysis was carried out at a subcritical state of water to obtain fatty acids from triglycerides of rapeseed oil, while the methyl esterification of the hydrolyzed products of triglycerides was treated near the supercritical methanol condition to achieve fatty acid methyl esters. Consequently, the two-step preparation was found to convert rapeseed oil to fatty acid methyl esters in considerably shorter reaction time and milder reaction condition than the direct supercritical methanol treatment. The optimum reaction condition in this two-step preparation was 270°C and 20 min for hydrolysis and methyl esterification, respectively. Variables affecting the yields in hydrolysis and methyl esterification are discussed. 

A catalyst-free supercritical methanol method for biodiesel fuel production was proposed with the optimum conditions of 350°C, 20 MPa, a molar ratio of 42 in methanol, and a 4-min treatment period (12-13). This method has been proved to produce a high yield, because of simultaneous reactions of transesterification of triglycerides and methyl esterification of free fatty acids (10). The only shortcoming of this one-step method is that it requires a severe reaction condition compared with the conventional commercial method with acid or alkaline catalyst. Consequently, our method would require a special alloy to cover the high temperature and high pressure of the reaction system. 

Therefore, the purpose of the present work was to study an alternative method for biodiesel fuel production that has a lower reaction condition than the one-step supercritical methanol method, through the two-step preparation consisting of hydrolysis of triglycerides in subcritical water and subsequent methyl esterification of the fatty acids by supercritical methanol treatment. In this article, we present various parameters affecting the yield of fatty acids in hydrolysis from triglycerides followed by methyl esterification of the fatty acids. We also compare the one- and two-step preparation methods and propose a production scheme of the latter. 

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