CHEMISTRY 1000 Topics of Interest #9: Biofuels, Cellulose and Wood

Biofuels can be produced in a number of different ways, including: Chemical breakdown of used cooking fats Extraction from crops with naturally high oil content (e.g. oil palm) Fermentation of sugars from crops grown specifically for that purpose (e.g. sugar cane, sugar beet). Starchy crops (e.g. corn) can be used too but are highly inefficient. Little of the sugar in biomass is actually present as free sugar or even starch. Most of it takes the form of cellulose. Like starch, cellulose is a polymer made of sugar units (one unit = glucose). Unlike starch, cellulose is more difficult to break down because of the way the sugar units are attached. Where Do Biofuels Come From? R. Rinaldi, R. Palkovits and F. Schuth Angewandte Chemie International Edition (2008) 47,

Starch Cellulose Where Do Biofuels Come From? R. Rinaldi, R. Palkovits and F. Schuth Angewandte Chemie International Edition (2008) 47, one sugar unit (“monomer”)

If it were possible to more easily break down cellulose into its constituent sugars (or even shorter chains of sugars), the more abundant cellulose could also be used as a source of biofuels. Cellulose and wood dissolve in ionic liquids (!) called alkylmethylimidazolium salts: You can see why this ionic compound might not form a solid lattice like the ionic solids we’ve looked at this term. Cellulose and Biofuels R. Rinaldi, R. Palkovits and F. Schuth Angewandte Chemie International Edition (2008) 47,

After the cellulose has been dissolved in the ionic liquid, the solution can be passed over a solid acid catalyst which breaks it down to shorter chains of sugars that could potentially be fermented to give biofuels from a wider variety of sources than is currently feasible. This process even works on wood! Cellulose and Biofuels R. Rinaldi, R. Palkovits and F. Schuth Angewandte Chemie International Edition (2008) 47,