Hemicelluloses derived from biomass are presently underutilized. In order to develop more profitable biorefinery processes, the mechanism responsible for hemicellulose removal by pretreatments has to be further explored. The hydrothermal dissolution profile of the wood components cellulose, hemicelluloses, and lignin of a hardwood mixture during autohydrolysis in a modified Dionex ASE-100 is described. Well-closed material balances were obtained for lignin-free yield, xylan, and glucomannan when comparing the solid and liquid phases. Xylo-oligomers were the predominant component in the extract. Xylan initially dissolved as oligosaccharides and then slowly depolymerized into monomeric xylose. The residual xylan in wood was only slightly deacetylated. A smaller amount of glucomannan was removed as oligosaccharides. Arabinose and galactose were completely removed from wood as monomers at the end of the extraction process. Initially all acetyl groups were removed while still bound to oligosaccharides. Then, acetic acid was released by deacetylation of the dissolved oligosaccharides.

A hydrothermal dissolution profile of wood components cellulose, hemicelluloses, and lignin of hardwood during autohydrolysis for 100 min at temperatures from 130 to 1708C in a modified accelerated solid extraction system (Dionex ASE-100) is described. The content of cellulose, hemicelluloses, lignin, acetyl, and uronic acid groups remaining in the extracted wood were determined. The extract was analyzed for oligosaccharides and monosaccharides, lignin, acetic acid, uronic acid, furfural, and hydroxymethylfurfural. Xylo-oligomers are the predominant component in the extract at temperatures higher than 1508C. At temperatures higher than 1608C, small amounts of furfural and hydroxymethylfurfural are generated. Most of the arabinan and galactan are removed from the wood at 1608C. The xylan remaining in the wood is acetylated at the same degree as in the original wood. In the extract, the ratio of acetyl groups bound to xylooligosaccharides decreases with increasing temperature. The content of uronic acid groups found in the extract obtained after autohydrolysis at TG1508C is significantly smaller than that calculated from the decrease in uronic content of the wood.

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