The Elements Of Biodiesel
With growing environmental awareness, biodiesel has become a booming industry, the hot new field.
On the contrary, the chemistry behind biodiesel is actually quite simple.
In organic chemistry, biodiesel is classified as an ester: a compound composed of an alcohol attached to an acid. Imagine biodiesel to be a very long carbon chain, with an ester bond (COO) somewhere in the middle.
To be completely truthful, the ester bond is not in the middle. This is because biodiesel uses short alcohols and long acids. Frequently methanol and ethanol, with one and two carbons each, are the alcohols of choice.
Long acids found in biodiesel include oleic acid, with 18 carbons, palmitic acid, with 16 carbons, and linoleic acid, with 18 carbons.
How is biodiesel made?
Do we simply mix together an alcohol with a long acid? Where do we get the alcohol and the long acid?
Biodiesel manufacturing uses alcohol, but not long acids. Instead, it uses oils and fats, such as vegetable oil or lard. Often biodiesel will be made with second-hand oils or fats, such as those from a local KFC or McDonalds.
However, biodiesel made with fresh oils and fats burn cleaner, as they contain fewer contaminants.
Why do we choose to use fats and oils?
They don't sound anything like acids. In reality, however, long acids are an essential component of lipids. A lipid is made up of glycerol, with three attached long acids. The lipid will be mixed with alcohol.
Visualize the reaction as follows. Firstly, the lipid breaks up into glycerol and three long acids. The glycerol, a type of alcohol itself, does not react with alcohol. The long acids bump around randomly in the mixture until they find alcohols. The acid and alcohol instantly attract each other and bond, creating biodiesel.
This picture, again, is not quite accurate. If one simply mixes biodiesel and alcohol, nothing will happen. Why? It's all a matter of stability and energy. The universe likes to keep things at their most stable configuration. A fat is happy being a fat. It doesn't want to break up into glycerol and long acids.
To cause the fat to break up, we need to tempt the fat with an even more stable configuration. For this reason, we add sodium hydroxide, a base, into the mixture. Sodium hydroxide breaks up into sodium cations and hydroxide anions.
The glycerol in the fat lusts after the hydroxide anions. Conversely, the long acids are attracted to the sodium cations. Consequently the fat disintegrates into a glycerol and three long acids. This decomposition, facilitated by sodium hydroxide, allows biodiesel to form.
Why does burning biodiesel produce energy?
Biodiesel is really not too different from standard petroleum. Biodiesel and petrol both contain long chains of carbons. The only difference lies in the ester bond. However, when the chain of carbons is so long, the effects of the ester bond are negligible.
This is why biodiesel is a fuel.
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Filed under Biodiesel by on May 8th, 2010. 
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