Abstract
Biomass has been an important energy source for mankind since the beginning of civilization. Ligno-cellulosic biomass is the most abundant organic source on earth, with an annual production in the biosphere of about 170 billion metric tons making it the most important renewable chemical and energy resource. Besides its largest use as building material, Ligno-cellulosic materials are also used to make paper. The three main components of lingo-cellulosic materials are cellulose, hemicellulose and lignin. Lignin has the highest calorific value while cellulose is the strongest component with hemicellulose among the lowest of both heating value and strength contribution. When chemically pulping lingo-cellulosic materials, predominantly cellulose is obtained as a solid product and converted to paper turning the other components into either process heat or waste. Turning hemicellulose into higher value products can be beneficial to the paper industry. In this study, hot-water extraction is examined for extracting value-added products prior to pulping. Besides the minor (less than 5%) extractives, hemicelluloses are the most easily separable main component of hardwood and grassy woody biomass and thus forms the bulk of the wood extracts obtained in the hot-water extraction. Xylan is the main polymeric molecule in hardwood and all angiosperm hemicelluloses. Hardwood xylan is a polymer made of beta-xylopyranose units linked through (1 -> 4)-glycosidic bonds, where arabinose, acetyl groups, and uronic acids are also present as lateral chains. Hydrolysis of hemicelluloses, especially xylan, occurs simultaneously in the extract liquor during the extraction process. Hydrolysis produces 5-carbon sugars (mainly xylose), 6-carbon sugars (mainly glucose), and acetic acid. Mass removal and chemical compositions in the hot-water extracts have been obtained to show the opportunity to turn a pulp mill into biorefinery by inserting an extraction step prior to pulping.