What is Biodiesel?

Biodiesel is an alternative fuel similar to conventional fossil diesel. Biodiesel can be produced from straight vegetable oil, other fats or waste cooking oil. The process used to convert these oils to biodiesel is called transesterification.  The largest source of suitable oil comes from oil crops such as rapeseed, palm, sunflower, peanut or soybean.

Over one hundred years ago, Rudolf Diesel invented a new type of car engine that operated at a higher compression ratio and didn't have spark plugs. The first thing that he noticed was that it was about 30% more efficient than a petrol engine and, also, he could run it on vegetable oil. However, the engine was soon adapted for use with fossil fuels as they appeared to be plentiful and were very much cheaper than vegetable oil. In the 1930s and 1940s vegetable oils were used as diesel fuels from time to time, but usually only in emergency situations.

Recently - because of increases in crude oil prices, the realisation that fossil oil reserves are low, and environmental concerns - there has been a renewed focus on using vegetable oils and there are now once again a few companies producing biodiesel fuels commercially.

Vegetable Oil

Each type of vegetable oil has its own properties and the most important consideration for conversion to biodiesel is melting point. The vegetable oil molecule is composed of three long carbon chains on a glycerol 'backbone' and its properties are determined by the individual 'fatty acid' chains. Rapeseed oil, for example, may be composed of different combinations of about 6 different fatty acids and each one of these creates a unique molecule, with unique properties. Some waste oil contains 'free fatty acid', which is a result of water in fried food reacting with the triglyceride to split it up into it's four components.  Rapeseed oil is generally the ideal as it is relatively thin.

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