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Transesterification (Chemical Conversion of Biodiesel)

The manufacturing of biodiesel from vegetable oils (e.g. soy, canola, jatropha or sunflower seed) or animal fats, involves the base-catalyzed transesterification of fatty acids with methanol or ethanol to give the corresponding methyl esters or ethyl esters. Glycerin is an inevitable byproduct of this reaction.

Vegetable oils as animal fats are triglycerides composed of three chains of fatty acids bound by a glycerin molecule. Triglycerides are esters. Esters are acids, like fatty acids, combined with an alcohol. Glycerine (= glycerol) is a heavy alcohol. In the conversion process triglyceride esters are turned into alkyl esters (= biodiesel) using a catalyst (lye) and an alcohol reagent, e.g. methanol, which yields methyl esters biodiesel. The methanol replaces the glycerin.

The glycerine - the heavier phase - will sink to the bottom. Biodiesel - the lighter phase - floats on top and can be separated, e.g. by decanters or centrifuges. This conversion process is called transesterification.

The conventional esterification reaction in batch processing tends to be slow, and phase separation of the glycerin is time-consuming, often taking 5 hours or more.