Biodiesel from fat or oil produces a large amount (about 10%) of glycerol (HOCH2CH[OH]CH2OH) as a by-product. Large-scale commercial production of biodiesel can therefore bring a huge amount of glycerol into the market. For example, for every kg of biodiesel, 0.1 kg of glycerol is produced (86% FAME, 9% glycerol, 4% alcohol, and 1% fertilizer) (www. biodiesel. org). If produced in the required purity (>99%), glycerol may be sold for cosmetic and pharma­ceutical production, but that market is not large enough to absorb it all. There­fore, alternative commercial uses need to be explored. These include:

• Catalytic conversion of glycerol into biogas (C8-Ci6 range) (Hoang et al.,

2007)

• Liquid-phase or gas-phase reforming to produce hydrogen (Xu et al., 1996)

A large number of other chemicals may potentially come from glycerol. Zhou et al. (2008) reviewed several approaches for a range of chemicals and fuels. Through processes like oxidation, transesterification, esterification, hydrogenolysis, carboxylation, catalytic dehydration, pyrolysis, and gasifica­tion, many value-added chemicals can be produced from glycerol.