Actually, I'm pretty sure I'll find that good biodiesel is 100% fatty acid monoester, which has more than 90% of the energy density of dino-diesel, and better combustion characteristics. Yes, the production process might use chip fat and methanol, but there is a chemical change takes place. If you represent a fatty acid as
RC02H
then the fat (or oil) associated with it is
(RCO2)3C3H5
Fat reacts with a simple alcohol (in this case methanol) in the presence of an alkali to form a fatty acid ester (biodiesel) and glycerine: a process called "transesterification". These two are immiscible and separate (with luck).
(RCO2)3C3H5 + 3CH3OH -> 3RCO2CH3O + C3H5(OH)3.
The fatty acid ester might have a chemical formula like
C17H35CO2CH3OH
(methyl stearate) which is similar enough to the C18H38 that makes up a typical fraction of dino-diesel that one can replace the other.
It is unreacted methanol that banjaxed the Top Gear car. They should have removed it from the end-product, but they didn't. For various reasons (in particular, the alkali reacting with free fatty acids to form soaps, which prevent complete separation of the glycerine from the monoester) that removal can be hard.
RC02H
then the fat (or oil) associated with it is
(RCO2)3C3H5
Fat reacts with a simple alcohol (in this case methanol) in the presence of an alkali to form a fatty acid ester (biodiesel) and glycerine: a process called "transesterification". These two are immiscible and separate (with luck).
(RCO2)3C3H5 + 3CH3OH -> 3RCO2CH3O + C3H5(OH)3.
The fatty acid ester might have a chemical formula like
C17H35CO2CH3OH
(methyl stearate) which is similar enough to the C18H38 that makes up a typical fraction of dino-diesel that one can replace the other.
It is unreacted methanol that banjaxed the Top Gear car. They should have removed it from the end-product, but they didn't. For various reasons (in particular, the alkali reacting with free fatty acids to form soaps, which prevent complete separation of the glycerine from the monoester) that removal can be hard.
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