| The first part of this research focused on the kinetic study of dilute acid hydrolysis of cellulosic biomass. Paying special attention to the fact that the reaction is heterogeneous, we find that the acid-catalyzed hydrolysis is controlled not only by the temperature and the acid concentration but also by the physical state of the cellulose. Under low temperature and acid conditions the cellulose structure stays in stable crystalline form, prevailing reaction mode thus being endwise hydrolysis. Under those circumstances, glucose becomes the main sugar product. Consequently, the conventional two sequential first-order kinetics becomes applicable. However, when temperature and/or acid concentration is raised to a certain level, the cellulose structure becomes unstable most likely by breakage of hydrogen bonding (HB), the primary force that holds the cellulose chains. Once the crystalline structure of the cellulose is disrupted, acid molecules can then penetrate into the inner layers of the cellulose chains. We also find that the breakage of HB occurs within a narrow range of temperature, showing a rather abrupt devastation of cellulose supramolecular structure. On the basis of these findings, a comprehensive kinetic model is proposed that includes a parallel reaction pathway (cellulose-oligomers-glucose) along with other previously known reactions. This model is in full compliance with our recent experimental data obtained under various conditions and reactor types.; The first-order kinetics parameters for glucose decomposition are also determined and a simplified kinetic model developed with the best-fit parameters. However, the glucose disappearance rate in actual hydrolysis process was faster than the model predicted due to the recombination of glucose with acid soluble lignin and metal or/and metal ions catalyzing glucose decomposition.; Another part of this work studied methods to generate useful chemicals by oxidation of lignin from the acid hydrolysis process. Oxidative cracking of acid hydrolysis reprecipitated lignin (HRL) by both hydrogen peroxide and molecular oxygen was investigated as ways to produce potentially useful chemicals. The chemical components from the oxidative reaction have been identified. The optimal oxidation conditions were explored and the reaction mechanisms were discussed. The yields of aromatic chemicals as well as organic acid were reported. |
