Cellulose Processing Via Acidic Hot Water

One technical hurdle to overcome in using cellulose as a renewable feedstock to make fuels and chemicals is transforming the glucose polymer chain into readily usable monomeric sugars. Cellulose typically is hydrolyzed by liquid acids to form glucose, which subsequently is hydrogenated to prepare sorbitol, mannitol, and other polyols. Haichao Liu and coworkers at Peking University, in Beijing, have come up with a potentially greener and less expensive method for cellulose conversion that avoids handling corrosive acids: The team uses hydronium ions (H₃O⁺) formed in situ in hot water to make glucose followed by instantaneous hydrogenation of the glucose over a carbon-supported ruthenium catalyst to form polyols (Angew. Chem. Int. Ed. 2007, 46, 7636). The Peking researchers take advantage of water's propensity to form H₃O⁺ at temperatures above 200 ^oC (near-critical water)—a property already utilized for some acid-catalyzed reactions. The in situ acid formation is reversible upon cooling, which should eliminate problems associated with acid recovery and waste disposal, they write.