| The fermentation of lignocellulose to methane, a potential renewable energy resource, is limited by lignocellulose's lignin content and the crystallinity of cellulose. Autohydrolysis, aqueous heat treatment under pressure at temperatures from 175 to 250(DEGREES)C without chemical addition, is a potential pretreatment for increasing the fermentability of lignocellulose. Factors affecting the rates of product formation and decomposition during staged autohydrolysis were determined in order to find conditions that enhance the production of fermentable products.; Staged autohydrolysis and biodegradability/toxicity pretreatments were performed in bomb-type autoclaves, while kinetic studies were conducted in a constant temperature bath. Anaerobic serum-bottle assays were used to determine the biodegradability and toxicity of the products from autohydrolysis. High performance liquid chromatography was used to identify and quantify the various soluble products resulting from autohydrolysis of lignocellulose.; Staged autohydrolysis of white fir increased the production of biodegradable products. The first stage at mild conditions solubilized hemicellulose, and subsequent stages at more severe conditions solubilized the cellulose, but carbohydrate decomposition also occurred. The principal identified soluble products formed were monosaccharides, 2-furfural, and 5-hydroxymethyl-2-furfural. These compounds were highly biodegradable. However, unidentified soluble products and humic solids from monosaccharide decomposition were not as fermentable.; The kinetics of monosaccharide decomposition and product formation were evaluated as a function of temperature and pH. The rate of monosaccharide decomposition was subject to general acid-base catalysis with temperature modeled by the Arrhenius relationship. Monosaccharide decomposition was minimized at pH between 2 and 2.5. The order of decreasing monosaccharide stability during autohydrolysis was glucose, galactose, mannose, and xylose. Decomposition of 2-furfural and 5-hydroxymethyl-2-furfural was acid catalyzed; however, levulinic acid formation occurred only when the pH was 2.5 or less. The formation of humic solids and unidentified soluble products from monosaccharide decomposition was a function of pH, increasing as the pH increased from 2 to 4.; A model was developed which accounts for the major products from staged autohydrolysis of lignocellulose. Application of the model indicated that the formation of biodegradable products is optimized when the pH is less than 3. |
