INFORM November/December 2025

BYPRODUCTS

inform November/December 2025, Vol. 36 (10) • 11

instance, blends of fuel containing 5 to 20 percent biodiesel are common. Because biodiesel is derived from non-fossil fuel sources, it is sometimes considered a carbon neutral fuel. This, and its ability to reduce use of petroleum resources, attracted the attention of policymakers in the United States and Europe, who started requiring use of biodiesel in the early 2000s. For instance, the European Union once set a target of having seven percent of diesel sold be biodiesel by 2015. Similarly, Brazil expanded the use of biodiesel derived from soybean oil. While conventional diesel is made by refining petroleum, biodiesel is produced using a variety of lipids like vegetable oil. Producers use a chemical process known as transesterifica

tion, reacting lipids with alcohol in the presence of a catalyst like sodium hydroxide. This reaction combines one oil molecule and three molecules of methanol to produce three fatty acid methyl ester molecules, in other words biodiesel, and one mole cule of glycerol. Producers then separate the resulting biodiesel and glycerol and further refine the fuel, leaving crude glycerol behind. But with about 10 percent of the mixture by weight being glycerol, there is a lot of it left over. Some estimates have somewhere between 65 and 75 percent of crude glycerol being treated as waste, largely due to economic factors. This is because glycerol made during biodiesel production has a purity of around 60 to 80 percent at most, with it being

Mixed methyl esters (Biodiesel)

O

O

O

H 3 C-O

R1

O

NaOH CH 3 OH

H 3 C-O

R1

O O O O O

R2

H 3 C-O

R3

R2

Transesterification

R3

OH OH OH

Triacylglycerol

Glycerol

The alkaline catalyzed transesterification reaction in the formation of biodiesel from triacylglycerols (TAGs) (R1, R2 and R3 correspond to unique fatty acids attached to the glycerol backbone of the TAG or alkyl ester). Source: Ashby, et al. , JAOCS , 88, 7, 2011.