“Near-Critical Water” Converts Lignin Into Biofuel Precursors

When ligno-cellulosic plant biomass (for example, wood) is used for ethanol production, only the cellulose component is usually utilized. The lignin component is often left as residue and unutilized. Lignin molecules are generally composed of small hydrocarbon chains linked by carbon-oxygen-carbon bonds. The small hydrocarbon chains are potential raw materials for biofuel production, if these can be broken off from the carbon-oxygen-carbon bonds. Breaking down the C-O-C bonds between chains, while leaving those within chains intact, is said to be a “difficult balancing act”. Getting the right conditions for reliably breaking off the carbon-oxygen-carbon links is said to be the key. Recently, Professor Yuan Kou and his colleagues from Peking University (Beijing, China) used “near-critical water” as the reaction solvent to achieve this breakthrough. A reaction mixture consisting of lignin, “near-critical” water (water at a temperature of about 250 ^oC to 300 ^oC/ pressure at about 7,000 kilopascals), a suitable catalyst (platinum-carbon) and an organic additive (dioxane), was found to yield hydrocarbon products which can be easily separated and processed into biofuels. Separation of the product from the reaction mixture can be easily achieved by just cooling the water and then drawing off the oily layer. The processing of the hydrocarbon product after processing yielded three components: (1) C8 to C9 alkanes (suitable for gasoline), (2) C12 to C18 alkanes (suitable for diesel) and (3) methanol.

Related information on lignin and its properties:
http://www.lignin.org/01augdialogue.html
http://en.wikipedia.org/wiki/Lignin