Batch process esterification, fatty acid methyl

Figure 6 shows the Henkel continuous process of fatty acid esterification. The reaction is carried out at a pressure of approximately 1000 kPa and a temperature of 240°C. One advantage of this process is the excess methanol can be kept significantly lower at 1.5 1 molar ratio of methanohfatty acid versus the batch process at 3—. 1 molar ratio. The methyl ester, having undergone distillation, does not require further refining. The excess methanol is rectified and reused (15). 

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> ° ° ... 

Saka and Kusdiana (2001) at the University of Kyoto investigated methyl-esterification in supercritical methanol without using any catalyst. The experiment was carried out in a batch-wise reaction vessel preheated at 350 and 400 °C at a pressure of 45-65 MPa. In a preheating temperature of 350 °C, 240 s of supercritical treatment with methanol was sufficient to convert the rapeseed oil to FAME, and, although the prepared FAME was basically the same as those of common method with an alkaline catalyst, the yield of FAME obtained at 350 °C was found to be higher than that obtained at 400 °C. The supercritical methanol process required a shorter reaction time and a simpler purification procedure. In addition, by using the supercritical methanol method, FAME was produced not only from triglycerides but also from free fatty acids. 

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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