Ionic-Liquid-Phase Hydrolysis of Pine Wood

Depolymerization of cellulose and hemicellulose from loblolly pine wood is studied in the ionic liquid 1-butyl-3-methylimidazolium chloride, which is capable of dissolving carbohydrates and lignin. In the presence of an acid catalyst, the carbohydrate fraction is converted into water-soluble products under milder conditions than reported for similar reactions in the aqueous phase. The water-soluble products included monosaccharides, oligosaccharides, furfural, and 5-hydroxymethylfurfural (HMF). The lignin fraction is recovered as a solid residue. It is found by C-13 CP MAS NMR spectroscopy that chemical modifications of lignin occurred only to a very moderate extent. The influence of the reaction temperature, water content, and acid concentration is investigated. In particular, the presence of water is found to reduce the solubility of carbohydrate but also to be required for its conversion. Under harsh conditions (high temperature, high acid concentration), solid degradation products, so-called humins, form. The main building blocks of humins are sugars that are linked by additional components forming linkages that are more resistant to hydrolysis than glycosidic bonds in carbohydrates.