Batch process transesterification, fatty acid

The oil, which is free of fatty acids, is then dried and transesterified (Fig. 83). The batch transesterification process represents the usual state of technology [202]. The process is operated in as simple a way as possible. 

The principles of biodiesel synthesis are relatively simple oleochemical reactions (see Chapter 9.1) and have been known and applied for many decades (Figure 8.5)." The basic technology consists in a catalyst induced transesterification of a vegetable oil in a batch, semi-batch or continuous process to create a fatty acid methyl ester (FAME). The catalyst used is a strong base,... 

Fatty acid esters of mono- and polyfunctional alcohols are the workhorses of oleochemistry. In many fields of application fatty acid methyl esters replace fatty adds because they are less corrosive. Chemical reactions can often be carried out under milder conditions. They have lower boiling points and require less energy to distil and to fractionate than the corresponding fatty acids. The elimination of methanol from the reaction products can be more easily achieved than that of water. Therefore fatty acid methyl esters are primarily used for the production of saturated and unsaturated fatty alcohols. Methyl esters are manufactured by acid catalyzed esterification of fatty acids in counter-current reaction columns or by alkaline transesterification starting directly from the triglyceride oils in a batch, semi-batch or continuous process (Figure 9.1.37> ° ° ... 

Esterification is carried out at 200-250 °C under slight pressure with acidic or alkaline catalysts. An excess of methanol and an elimination of water during reaction promotes ester formation. Batch and continuous processes are in practical use. Esterification is used especially if fractionated or special fatty acids are the starting material to make defined methyl esters (e.g., methyl oleate from oleic acid from high-oleic - sunflower). Transesterification is the predominant process for manufacturing methyl esters. Triglycerides with no free fatty acids react under mild conditions (SOTO °C, atmospheric pressure). Because most fats and oils have considerable contents of ffa, it is necessary to either eliminate them or chose transesterification conditions that allow also esterification of ffa. In technical processes, the reaction is carried out at 220-250 °C and 9-10 MPa (90-100 bar). Under these conditions, fats and oils that contain up to 20% ffa can be transferred into methyl esters. The resulting esters can be purified by - distillation. 

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