INFORM November/December 2025

12 • inform November/December 2025, Vol. 36 (10)

Possible reaction mechanism for glycerol oxidation over an Au/Al 2 O 3 catalyst. FA, formic acid; GA, glyceric acid; GCA, glycolic acid; LA, lactic acid. Source: Chida, et al. , JAOCS , 97, 12, 2020.

lower in some cases. Crude glycerol is a mixture of pure glycerol and other chemicals from the transesterification process. This includes water, left over methanol, dissolved material from the catalyst and non-glycerol organic matter, commonly referred to as MONG, consisting mostly of lipids that did not react during the transesterification process. These impurities make it eco nomically infeasible for producers to sell crude glycerol. To counter this, larger biodiesel producers will take steps to purify crude glycerol. They will use distillation processes to remove water and excess methanol and filter out MONG and other chemicals like salts and sulfur compounds. This can get crude glycerol up to a purity of 95 to 99.5 percent, mak ing it more attractive to the market. However, contaminant levels vary from batch to batch depending on reaction condi tions and the lipid feedstocks used. For example, crude glyc erol made from pure vegetable oil will be notably different from a batch produced from waste cooking oil. Additionally, these purification steps add costs in the form of equipment and energy, putting them out of the reach of smaller biodiesel producers. CHEMICAL WITH A THOUSAND FACES Glycerol is a simple molecule made of a chain of three carbon atoms, each bonded to a hydroxyl group. Its structure and com position makes glycerol water soluble and hygroscopic. Glycerol is also non-toxic to humans and the environment. This has made it attractive for use in food, pharmaceuticals and cosmetic prod ucts. Additionally, glycerol can be used to supplement animal feed or as fertilizers. In the past most of the glycerol used in this way came from petroleum sources, but greener sources like purified crude glycerol have been gaining ground.

Although glycerol itself is extremely useful, its potential as building blocks for other chemicals is nearly limitless. As with its useful physical characteristics, this comes down to the mol ecule’s chemical structure. One of the carbon bonds in glyc erol is relatively weak. This means the molecule can be broken apart relatively easily and recombined into other chemicals ranging from artificial sweeteners to a variety of useful acids to monomers and polymers crucial for plastic production. “Glycerol is a very versatile molecule,” said Mickael Capron, professor of chemistry at the University of Lille in Lille, France. “You can do a lot of things with it.” Chemists can remix the carbon, oxygen and hydrogen atoms in glycerol with many different chemical processes. For instance, you can use oxidation to produce lactic acid, dehy dration to make acrolein, hydrogenation to convert glycerol into 1,3-propanediol, a chemical heavily used in plastics pro duction, and pyrolysis to make aromatics like benzene that are useful as fuel additives. The choice of process is driven by the desired end product. “It depends really on the products you want to target,” said Capron. Recently, researchers have been looking into new ways to convert glycerol into fuels like propane. Researchers at Aston University in Birmingham, England recently developed a two stage process where they first generated hydrogen gas from glycerol, which they used in the second stage to produce pro pane. In many cases the hydrogen used in chemical synthe sis comes from fossil fuel sources, making this an important development. “Producing renewable hydrogen is a very important energy vector and a high-demand chemical intermediate in