Biomass Valorization in High-temperature Liquid Water

Conversion of biomass resources to fuels and chemicals is a highly effective approach for a biomass valorization as a prospective alternative to petrochemical processes. Biomass conversion using water as a reaction medium is desirable because water is non-toxic and environmentally friendly. Biomass valorization techniques in high-temperature liquid water and supercritical water are reviewed, such as (i) dehydration reactions of biomass-derived polyalcohols to cyclic ethers and (ii) gasification reactions of lignin to fuel gases. (i) Cyclic ethers were produced by the intramolecular dehydration reactions of biomass-derived polyalcohols in high-temperature liquid water without acid catalysts. Addition of carbon dioxide accelerated the dehydration in high-temperature liquid water because the added carbon dioxide dissolves in water to form carbonic acid. (ii) Charcoal-supported ruthenium salts were active for lignin gasification at 673 K in supercritical water, in which ruthenium (III) species were reduced to ruthenium metal particles.