How biodiesel is made

Biodiesel chemistry is older than the diesel engine. Vegetable oil was first split this way in 1853.

stations: 5
things upstream: 10
raw sources: 6
steps from the ground: 4

The short version

Biodiesel is made from vegetable oil, animal fat or used cooking grease by transesterification. The fat reacts with methanol and a catalyst, which swaps the glycerol backbone for methyl groups and leaves fatty acid methyl esters. About 100 kilograms of glycerol come off for every tonne of fuel.

Filter the fat or oil

Vegetable oil, animal fat or frying oil is strained and cleaned. Free water and solids would upset the reaction.

Goes in
Vegetable oil
Prepare the methoxide

Methanol is the cheapest alcohol, so most plants use it. It is converted to sodium methoxide, which drives the reaction.

Goes in
Methanol
React oil with alcohol

The oil and the methoxide are stirred together in a reactor. Each fat molecule splits into long-chain methyl esters and free glycerol.
Let the glycerol settle

Two layers form as the mixture rests. Glycerol sinks, and the lighter esters, which are the biodiesel, float on top.
Wash and dry the fuel

The biodiesel layer is washed to remove leftover catalyst and soap, then dried. It is tested against standards before it is blended with regular diesel.

End of the lineBiodiesel Next it goes into diesel fuel.

Worth repeating

For every tonne of biodiesel, about 100 kilograms of glycerol are produced.
Rudolf Diesel never designed his engine for peanut oil, though one ran on it at the 1900 Paris Exposition.
Blends under 20 percent biodiesel work in diesel equipment with little or no modification.