How glycerin is made

Glycerin is the sweet, syrupy backbone of every fat, and it is now a surplus byproduct of biodiesel.

stations: 6
things upstream: 14
raw sources: 8
steps from the ground: 4

The short version

Glycerin comes from fats and oils. When vegetable oil or animal fat is split with caustic soda or reacted with an alcohol, its three fatty acid tails come off and glycerin is left in the water. The watery glycerin is evaporated, distilled under vacuum and filtered to remove color and odor.

Split the fat

Palm oil, other vegetable oils or tallow are reacted with sodium hydroxide, which breaks each fat molecule into soap and glycerol. Biodiesel plants use an alcohol such as methanol instead and split off glycerol the same way.

Goes in
Palm oil Vegetable oil Caustic soda Methanol
Settle the layers

After the reaction, the mixture is left to settle or spun in centrifuges. The heavier, glycerin-rich water drains away from the soap or biodiesel.
Evaporate off the water

Water is boiled out of the crude glycerin in multiple-effect evaporators, which reuse steam. Salt and other impurities crystallize and are filtered off.
Distill it under vacuum

Glycerol boils at a high temperature, so the distillation chamber is held under vacuum. Low pressure lets it vaporize without scorching.
Bleach and filter

Activated carbon removes color and smell from the distilled liquid. The clear syrup is filtered once more.
Drum and tank it

Glycerin is stored in tanks, drums or totes. Commercial glycerin sold as glycerine is typically about 95% pure.

End of the lineGlycerin Next it goes into soap, toothpaste, sunscreen and 4 more.

Worth repeating

Since around 2010 there has been a large surplus of glycerol as a byproduct of biofuel production.
Triglycerides can be saponified with sodium hydroxide to give glycerol and a fatty sodium salt, which is soap.