EnergyEnviron.Sci.http://doi.org/jwd(2012)

Generating biofuels from waste biomass eliminates the competition between biofuels and food sources for arable land. Waste biomass contains a mixture of chemically similar components such as cellulose and hemicellulose, but current approaches require these sugars to be separated before they can be turned into useful feedstocks. This separation step can account for up to 30% of the capital costs required to set up a biofuel production plant. Simultaneous conversion of these different components would alleviate the need for costly and complicated pre-treatment steps while still maximizing the yield of useful products.

To address this problem, James A. Dumesic and colleagues at University of Wisconsin-Madison in the USA have developed a method of simultaneously processing hemicellulose and cellulose in a single reactor. Using maize stover (the leaves and stalks left behind after harvesting) as the feed, either an open reactor or a batch reactor can be used to transform a mixture of cellulose and hemicellulose into useful chemical feedstocks. In the open reactor, hemicellulose is converted to furfural and levulinic acid is formed from cellulose. Furfural has a lower boiling point than the solvent or other products, enabling it to be continuously removed by distillation. The process is similar when configured as a batch reaction, however the furfural is also converted — through furfuryl alcohol — to levulinic acid and so no separation is required.

Catalytic reduction of levulinic acid gives gamma-valerolactone, which is also used as the solvent in both processes, and therefore simplifies the separation of the product downstream. Another added benefit is that gamma-valerolactone also solubilizes the degradation products that are typically formed while converting lignocellulose into chemical feedstocks, which is particularly useful to prevent the build-up of solid residue in a continuous flow reactor. The processes give a comparable amount of liquid fuel, in terms of useable energy content, as does the fermentation of maize stover to ethanol. Furthermore, the products can be used as precursor chemicals or processed downstream into liquid fuels.