Biodiesel

fuels from waste fat and cooking oil

Cooking oil is a triglyceride of a fatty acid (a special type of ester). With use it is contaminated and saturated.

What does saturated mean?
The double bonds (C=C) are changed to single bonds (C-C). The oil gradually changes to a fat. It is useless for cooking.

The change from waste to diesel fuel is simple chemistry.
Decompose the triglyceride into glycerine and a fatty acid (salt).

C₃H₅(OR)₃ + 3NaOH ® C₃H₅(OH)₃ + 3NaOR*

Produce a methyl ester of the fatty acid.

NaOR* + CH₃OH ® CH₃OR + NaOH

These methyl esters are more viscous than dieselene but are low in sulfur.

* R is usually C16H33 or CH18H35