A comprehensive kinetic model for dilute-acid hydrolysis of cellulose.
Acid-catalyzed hydrolysis is controlled not only by temperature and acid concentration but also by the physical state of the cellulose. Under low temperature and acid condition the cellulose structure stays in stable crystalline form. Therefore, the prevailing reaction mode is endwise hydrolysis. Glucose then becomes the main sugar product. However, when temperature and/or acid concentration is raised to a certain level, the cellulose structure becomes unstable by breakage of hydrogen bonding, the primary force that holds the cellulose chains. Once the crystalline structure of the cellulose is disrupted, acid molecules can penetrate into the inner layers of the cellulose chains. In support of this hypothesis, we have experimentally verified that a substantial amount of oligomers is formed as reaction intermediates under extremely low-acid and high-temperature conditions. We also found that the breakage of hydrogen bonds occurs rather abruptly in response to temperature. One such condition is 210 degrees C, 0.07% H2SO4. Glucose, once it is formed in the hydrolysate, interacts with acid-soluble lignin, forming a lignin-carbohydrate complex. This occurs concurrently with other reactions involving glucose such as decomposition and reversion. On the basis of these findings, a comprehensive kinetic model is proposed. This model is in full compliance with our recent experimental data obtained under a broad range of reaction conditions.
Xiang
Qian
Q
Department of Chemical Engineering, 230 Ross Hall, Auburn University, Auburn, AL 36849, USA.
Kim
Jun Seok
JS
Lee
Y Y
YY
D000821:Animal Feed; D002240:Carbohydrate Sequence; D002384:Catalysis; D002482:Cellulose / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007202:Indicators and Reagents; D007700:Kinetics; D008962:Models, Theoretical; D008969:Molecular Sequence Data; D032107:Populus / Q000737:chemistry
D007202:Indicators and Reagents; D002482:Cellulose