Glycerol is one of the frequently produced bioalcohols, because glycerol is a waste product of biodiesel production. However, glycerol is rarely considered a biofuel, because it is not easy to burn and therefore is only useful for non­combustion-based fuel uses.

Biodiesel is typically produced by the transesterification of lipids (vegetable oil, soybean oil, waste oil, etc.) with an alcohol (typically methanol). If methanol is employed, the transesterification results in the production of methyl esters, which is used as the fuel, and glycerol which is the by-product as shown in Fig. 11.2. A total of 100 kg glycerol is produced for every ton of biodiesel manufactured.10 The main problem with bioglycerol is twofold: (1) it is a waste product so it is low concentration and impure and (2) there has not been a market for bioglycerol. Since glycerol is part of the waste stream, it is in low concentrations and in a highly basic aqueous environment, because the catalyst for transesterification is typically sodium or potassium hydroxide. This can be fixed by neutralization and distillation, but that is not cost effective. Secondly, glycerol is not commonly used as a fuel, because it does not burn well and cannot be easily electrochemically oxidized.1115 However, it may be useful for other chemical purposes, because it can be used to produce glyceric acid and dihydroxyacetone. It is important to note that the biodiesel process is not really producing a bioalcohol, but it is using a low energy density bioalcohol (methanol) to produce a higher energy density bioalcohol (bioglycerol), which is different than using carbohydrates to produce bioalcohols.