Kinetic Modeling of Hardwood Prehydrolysis. Part I. Xylan Removal by Water Prehydrolysis
Keywords:Xylan, prehydrolysis, water prehydrolysis, autohydrolysis, kinetics, hardwoods, aspen, <i>Populus tremuloides</i>, birch, <i>Betula papyrifera</i>, elm, <i>Ulmus americana</i>, maple, <i>Acer rubrum</i>, southern red oak, <i>Quercus falcata</i>
AbstractThe kinetics of xylan removal from quaking aspen, paper birch, American elm, and red maple by water prehydrolysis (autohydrolysis) was reevaluated, and additional data for the water prehydrolysis of southern red oak were obtained. Xylan removal from these hardwood species can be modeled kinetically as the sum of two parallel first-order reactions—one fast and one slow. The rate constant for the fast reaction is highly correlated with the rate constant for the slow reaction for all species studied. The rate constant for initial xylan removal usually reported in the literature is actually a complex function of the rate constants for both the fast and slow reactions and is based solely on the initial data points. This paper presents an improved method for modeling xylan removal that allows modeling throughout the course of its reactions. The reason there are two different rates of xylan removal can be more easily explained on the basis of accessibility rather than any variability in the polymeric structure of the xylan being removed. Thus, the slow rate may be due to a portion of the xylan being embedded within or attached to the lignin via lignin-carbohydrate bonds.
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