Hemicellulose Pre-Extraction of Hardwood
A Southern US hardwood mixture was subjection to pre-extraction with water at 150 C. Well closed material balances wer obtained fro lignin-free yield, xylan and glucaomannan when comparing the solid and liquid phases. Xylan initially dissolves as oligosaccharides and then slowly depolymerizes into monomeric xlose. THe residual xylan in wood is only slightly deacetylated. The methyl-glucoronic anhydride/xylose ration in wood decreases significantly with increasing extraction time. A smaller amount of glucomannan is removed as oligosaccharides. Approximately 1% as cellulose dissolves mostly in polymeric form. Arabinan and galactan are completely removed from wood as monomers at the end of the extraction process. Initially all acetyl groupds are removed while still bound to oligosaccharides. Then acetic acid is released by deacetylation of the disssolved oligosaccharides. A significant amount of lignin (up to 5% based on wood) is extracted, part of which is still covalently bound to hemicelluloses.