**2. Biodiesel basics**

Biodiesel is produced from plant oils (soybean oil, cotton seed oil, canola oil), recycled cooking greases or oils (e.g., yellow grease), or animal fats (beef tallow, pork lard). Biodiesel is the result of a chemical reaction process on oils or fats called transesterification. A simple diagram of the transesterification process is shown in Figure 1. Vegetable oil, animal fats or waste oil react with alcohol in the presence of catalysts to form Biodiesel and Glycerin. Glycerin is a co-product of the biodiesel process. There are three distinct types of transesterification process: (1) Base catalyzed transesterification of the oil, (2) Direct acid catalyzed transesterification of the oil, and (3) conversion of the oil to its fatty acids and then to biodiesel. For the direct acid catalyzed transesterification of the oil, the transesterification process is catalyzed by bronsted acids, preferably by sulfonic and sulfuric acids. These catalysts give very high yields in alkylesters, but the reactions are slow, requiring, typically, temperatures above 100 °C and more than 3 h to reach complete conversion. The base-catalyzed transesterification of vegetable oils proceeds faster than the acid-catalyzed reaction and the alkaline catalysts are less corrosives than acidic compounds. From these three basic route to biodiesel production the base catalyzed transesterification of the oil present many advantages. First the base catalyzed transesterification has high conversion efficiency. With this process around 98 percent of all the reactants will effectively mix to produce biodiesel. This chemical reaction is also efficient at low temperature and low pressure. This is great advantages because it means that no heavy pressure unit or heating unit would be required. Furthermore this transesterification lead to a direct conversion and does not need any intermediate compounds to achieved biodiesel production.

#### **2.1 Reactants**

Two reactants are present during the chemical reaction. The first one is the triglycerides from the vegetable oil and the second is the alcohol. Triglycerides can have different alkyl groups as biodiesel can be made out of different kind of straight vegetable oil or waste vegetable oil. Two different kind of alcohol can be used: methanol or ethanol. These two alcohols are used in particular for this chemical reaction because there is very little space between triglycerides atoms for the alcohol to react with.
