What are plant oils?
Many plants can be processed to give an oil which can be used for many different applications, most of them are well-known within the kitchen, such as margarine, cooking oils and mayonnaise. Plant oils can – with a little bit of conversion – also be used as fuels for example as bio diesel. This is because they are made up of a short three carbon chain , off of each chain there are three much longer chains. If we break down the oil and break off the longer chains, we can use these longer chains to make fuels relatively easily.
(Now the A-Level bit)
This process is called Transesterification as we remove the original glycerol ester and replace it with the methanol group in its place. (The hydroxide acts as a catalyst) It’s kind of similar to a displacement reaction, as the methanol displaces the glycerol.
Glycerol-OOR + methanol –> Glycerol + Meth-OOR
How do we make fuels?
To break down the Plant oil, all that is needed is a strong base. (These contain OH– ions within them) by reacting the strong base with the plant oil, the long chain (fatty acid) part of the molecule breaks off leaving the short (glycerol) part separated.
Very usefully, these two parts are immiscible (which means they do not mix) and form two separate layers. The top layer is the useful bio fuel layer, the bottom layer is a glycerol layer which can be sold to make soaps.
Making biofuels class worksheet*
See also CLEAPSS PS67-10 and Hazcards 40B & 91
*Please note, do not try this at home, you are responsible for ensuring the safety of this practical and producing your own risk assessment.