Biodiesel is an alternative renewable fuel that can be made from amongst others, vegetable oils in a chemical process called transesterification, which involves a reaction with methanol, in the presence of a catalyst (usually sodium hydroxide [NaOH] or potassium hydroxide [KOH]), which also results in a bi-product glycerine or glycerol. In the frying process, the vegetable oil undergoes several reactions which leads to the formation of undesirable compounds such as polymers and free fatty acids, among others. Hence, the proper utilisation of such oils is important because of their disposal problems and negative impacts on the environment.
Biodiesel has substantially different properties and results in better engine performance. Biodiesel is most commonly used as a blend with petroleum diesel fuel. Most manufacturers of diesel vehicles and engines have approved the use of B5 (a blend containing 5% biodiesel and 95% petroleum diesel), and some export countries approve the use of blends up to B20 (20% biodiesel and 80% petroleum diesel) or higher. To ensure good performance in engines, biodiesel must meet quality specifications developed by the EU and SANS. Blends up to B5 may be found in conventional diesel fuel without additional labelling at the pump.