Zhu, Li (2005-08). Fundamental study of structural features affecting enzymatic hydrolysis of lignocellulosic biomass. Doctoral Dissertation. Thesis uri icon

abstract

  • Lignocellulose is a promising and valuable alternative energy source. Native
    lignocellulosic biomass has limited accessibility to cellulase enzyme due to structural
    features; therefore, pretreatment is an essential prerequisite to make biomass accessible
    and reactive by altering its structural features.
    The effects of substrate concentration, addition of cellobiase, enzyme loading,
    and structural features on biomass digestibility were explored. The addition of
    supplemental cellobiase to the enzyme complex greatly increased the initial rate and
    ultimate extent of biomass hydrolysis by converting the strong inhibitor, cellobiose, to
    glucose. A low substrate concentration (10 g/L) was employed to prevent end-product
    inhibition by cellobiose and glucose. The rate and extent of biomass hydrolysis
    significantly depend on enzyme loading and structural features resulting from
    pretreatment, thus the hydrolysis and pretreatment processes are intimately coupled
    because of structural features.
    Model lignocelluloses with various structural features were hydrolyzed with a
    variety of cellulase loadings for 1, 6, and 72 h. Glucan, xylan, and total sugar
    conversions at 1, 6, and 72 h were linearly proportional to the logarithm of cellulase
    loadings from approximately 10% to 90% conversion, indicating that the simplified
    HCH-1 model is valid for predicting lignocellulose digestibility. Carbohydrate
    conversions at a given time versus the natural logarithm of cellulase loadings were
    plotted to obtain the slopes and intercepts which were correlated to structural features (lignin content, acetyl content, cellulose crystallinity, and carbohydrate content) by both
    parametric and nonparametric regression models.
    The predictive ability of the models was evaluated by a variety of biomass (corn
    stover, bagasse, and rice straw) treated with lime, dilute acid, ammonia fiber explosion
    (AFEX), and aqueous ammonia. The measured slopes, intercepts, and carbohydrate
    conversions at 1, 6, and 72 h were compared to the values predicted by the parametric
    and nonparametric models. The smaller mean square error (MSE) in the parametric
    models indicates more satisfactorily predictive ability than the nonparametric models.
    The agreement between the measured and predicted values shows that lignin content,
    acetyl content, and cellulose crystallinity are key factors that determine biomass
    digestibility, and that biomass digestibility can be predicted over a wide range of
    cellulase loadings using the simplified HCH-1 model.

publication date

  • August 2005