THERMOCHEMICAL PRETREATMENT OF LIGNOCELLULOSE TO ENHANCE METHANE FERMENTATION .1. MONOSACCHARIDE AND FURFURALS HYDROTHERMAL DECOMPOSITION AND PRODUCT FORMATION RATES

Over a pH range 1-4 and temperatures from 170 to 230 degree C, the decomposition rates of xylose, galactose, mannose, glucose, 2-furfural, and 5-hydroxymethyl-2-furfural (5-HMF) were pseudo first order. The effect of temperature and pH on the pseudo first-order decomposition rate constants was modeled using the Arrhenius equation and acid-base catalysis, respectively. Decomposition rates of the monosaccharides were minimum at a pH 2-2. 5. Above pH 2. 5, the monosaccharide decomposition was base catalyzed, with acid catalysis occurring at a pH of less than 2 for glucose. The furfurals were subject to acid calysis at below 2. 5. Above pH 2. 5, the monosaccharide decomposition was base catalyzed, with acid catalysis occurring at a pH of less than 2 for glucose. The furfurals were subject to acid catalysis below ca. pH 3. 5. The hydrothermal conversion of glucose to its decomposition products during thermochemical pretreatment can be modeled as a combination of series and parallel reactions. The formation rates of identified soluble products from glucose decomposition, 5-HMF and levulinic acid, were also functions of temperature and pH. The rate of 5-HMF formation relative to glucose decomposition decreased as the pH increased from 2. 0 to 4. 0, with levulinic acid formation only detected when the pH was 2. 5 or less. For glucose decomposition, humic solids accounted for ca. 20% of the decomposition products.