Southern pineprehydrolyzates: Characterization of polysaccharides and lignin fragments

Prehydrolyzates obtained by treatment of southern pine chips at 175° with steam and water were examined in parallet studies. Carbohydrates were separated from other solids and fractionated into monosaccharides, low-molecular weight polysaccharides and highmolecular weight polysaccharides. The latter fractions were selectively subfractionated into series of glucomannans and galactoglucomannans using barium precipitation. The poly-saccharide fractions were characterized by gel permeation chromatography (gpc), the hemicellulose subfractions by periodate oxidation, vapor pressure osmometry, polarimetry, and end-group assay. Sugar ratios were determined on hydrolyzates of all fractions. Water prehydrolysis was shown to remove substantially more carbohydrates from the chips than steam prehydrolysis, 9.3% versus 3.3% (O.D. wood basis), and these carbohydrates had higher average molecular weight, contained more mannose per unit glucose and yielded more galactoglucomannans than those removed by steam. One of the galactoglucomannans from water prehydrolyzate had the highest number average molecular weight in this study: 3100 by end-group assay, 3800 by osmometry; polysaccharides of even higher molecular weight were indicated by gpc prehumps. Several monomeric lignin degradation products were identified in the methyl ethyl ketone soluble fraction of steam prehydrolyzate. Among these were coniferaldehyde, vanillic acid, vanillin, protocatechualdehyde, phydroxybenozic acid and, unexpectedly, a sizeable proportion of dihydroconiferyl alcohol.