This form of crude glycerol is often dark in appearance with a thick, syrup-like consistency.

This fuel can be made from any crude glycerol, regardless of the feedstock, including yellow grease.

Usually this crude glycerol has to be purified, typically by performing vacuum distillation.

As a result, a good fraction of crude glycerol is disposed of as waste.

Certain chemicals, such as crude glycerol, are specifically excluded from this chapter and are classified elsewhere.

As a result of increasing biodiesel production, formation of the byproduct, crude glycerol, has also increased.

However, with the increase in global biodiesel production, the market price for this crude glycerol (containing 20% water and catalyst residues) has crashed.

The use of crude glycerol as an additive to biomass for a renewable energy source when burned or gasified is also being explored.

The alcohol reacts with the fatty acids to form the mono-alkyl ester (or biodiesel) and crude glycerol.

Crude glycerol is purified to make various grades, such as dynamite grade, yellow distilled and chemically pure glycerol.

A great deal of research is being conducted to try to make value-added products from crude glycerol (typically containing 20% water and residual esterification catalyst) obtained from biodiesel production.

Biotechnology is one such technique: using particular enzymes to break down crude glycerol to form products such as 1,3-propanediol, 1,2-propanediol, succinic acid, dihydroxyacetone (glycerone), hydrogen, polyglycerols, and polyesters.

While glycerol is commonly used in food, pharmaceuticals, cosmetics, and other industries, increased production of crude glycerol has become very expensive to purify and utilize in these industries.

Crude glycerol from the hydrolysis of triglycerides can be purified by treatment with activated carbon to remove organic impurities, alkali to remove unreacted glycerol esters, and ion exchange to remove salts.