Biodiesel trans-esterification reaction

The process involves reacting the degummed oil with an excess of methyl alcohol in the presence of an alkaline catalyst such as sodium or potassium methoxide, reaction products between sodium or potassium hydroxide and methyl alcohol. The reaction is carried out at approximately 150°F under pressure of 20 psi and continues until trans-esterification is complete. Glycerol, free fatty acids and unreacted methyl alcohol are separated from the methyl ester product. The methyl ester is purified by removal of residual methyl alcohol and any other low-boiling-point compounds before its use as biodiesel fuel. From 7.3 lb of soybean oil, 1 gallon of biodiesel fuel can be produced. See FIGURE 12-5. 

Biodiesel fuel can be produced from jatropha oil using a fairly simple chemical reaction known as trans-esterification. In this process, the oil reacts with a simple alcohol (methanol/ethanol) in the presence of a catalyst (caustic soda/potash) and, under specified conditions such as a temperature of 65°C and normal atmospheric pressure, yields a mixture of methyl or ethyl esters which is the biodiesel. This fuel... 

The use of methanol offers the best results in the trans-esterification of oils and fats. Compared with other alcohols, methanol requires shorter reaction times and smaller catalyst amounts and alcohol/oil molar ratios [10,12,15,16,51,52]. These advantages lead to reduced consumption of steam, heat, water, and electricity, and use of smaller processing equipment to produce the same amount of biodiesel. Biodiesel applications continue to expand. Thus, in addition to its use as fuel, biodiesel has been employed in the synthesis of resins, polymers, emulsifiers, and lubricants [53-64]. Concerning the range of applications, new biodiesel production processes should be considered as alternatives to the production based on methanol. Currently, methanol is primarily produced from fossil matter. Due to its high toxicity, methanol may cause cancer and blindness in humans, if they are overexposed to it. Methanol traces are not desired in food and other products for human consumption [15]. In contrast, ethanol emerges as an excellent alternative to methanol as it is mainly produced from biomass, is easily metabolized by humans, and generates stable fatty acid esters. Additionally, fatty acid ester production with ethanol requires shorter reaction times and smaller amounts of alcohol and catalyst compared to the other alcohols, except methanol, used in transesterification processes [11,15,16]. 

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