Читать книгу Biodiesel Technology and Applications - Группа авторов - Страница 16

There can be many ways for biodiesel production but esterification and transesterification are the two most widely used methods. Esterification is the reaction of FFAs and alcohol to make FAAEs and water is released, while transesterification is the reaction of triglycerides or triacylglycerols (TAGs) with alcohol to make FAAE and glycerol is produced as by-product [9]. Transesterification is slower than esterification process because of its multiple steps or reactions. It is a three-step process to convert TAGs into FAAE. In the first step, TAG reacts with one molecule of alcohol to produce one molecule of FAAE and diacylglycerol (DAG). In second step, DAG further reacts again with one molecule of alcohol to produce one molecule of FAAE and monoacylglycerol and in the last step monoacylglycerol is converted into one molecule of glycerol and FAAE after reacting with an alcohol molecule. In each of these three steps, FAAEs are produced and in total one molecule of TAG and three molecules of alcohol are consumed to produce three molecules of FAAE and one molecule of glycerol [6–10]. Transesterification is a reversible reaction, and in order to make the reaction go forward to produce more biodiesel, we have to supply alcohol in large excess so that the reaction equilibrium shifts toward the product [36, 37].