BIODIESEL

In a 1912 speech, Rudolf Diesel said, "the use of vegetable oils for engine fuels may seem insignificant today, but such oils may become, in the course of time, as important as petroleum and the coal - tar products of the present time". The revival of biodiesel derived from vegetable oils started as a result of agricultural surplus in some European countries and under Kyoto protocol the need of reducing greenhouse gas CO₂ emissions. 
Biodiesel is a renewable fuel that is produced from a variety of edible and non-edible vegetable oils and animal fats.
The term “biodiesel” is commonly used for methyl or ethyl esters of the fatty acids in natural oils and fats, which meet the fuel quality requirements of compression-ignition engines.
Straight vegetable oils (SVO) are not considered as biodiesel. The straight vegetable oils have a very high viscosity that makes flow of these oils difficult even at room temperatures.  Moreover, presence of glycerine in the vegetable oil causes formation of heavy carbon deposits on the injector nozzle holes that results in poor and unacceptable performance and emissions from the engine even within a few hours of operation.

Biodiesel Production – Esterification of Oils

Biodiesel is produced by reacting vegetable oils or animal fats with an alcohol such as methanol or ethanol in presence of a catalyst to yield mono-alkyl esters. The overall reaction is given in Fig. 8.6.  Glycerol is obtained as a by-product.

Properties of Biodiesel

A variety of vegetable oils such as soybean, rapeseed, safflower, jatropha-curcas, palm, and cottonseed oils have been used for production of biodiesel.  Waste edible oils left after frying/cooking  operation etc., have also been converted to biodiesel for study of their performance. The biodiesel are also known as fatty acid methyl esters [FAME]. Recently non-edible oil produced from jatropha-curcas seeds has gained interest in India as this plant can be easily grown on wastelands. The properties of methyl esters of rapeseed and jatropha oils are given in Table 8.18.