Graduate Thesis Or Dissertation
 

Conversion of lignocellulosic biomass : analysis of substrate characteristics

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  • The objective of this research was to investigate the influence of physicochemical properties of lignocellulosic biomass on the rate and extent of cellulose conversion, i.e. the "hydrolyzability" of the substrate. The initial two parts of this thesis investigated the interactions between various components of pretreated biomass. The relevance of cellulase partitioning between the cellulose and non-cellulose components of pretreated switchgrass was determined. Furthermore, a method was developed to assess the changes in surface area of the non-cellulose fraction during saccharification. The overall conclusion from these studies was that for an optimally pretreated switchgrass sample the cellulose and non-cellulose components are fully disassociated and the non-cellulose fraction does not appear to interfere with cellulose conversion. The third study determined the changes in physicochemical properties of native and pretreated poplar during simultaneous saccharification and fermentation (SSF). While this study gave an unprecedented insight into the dynamics of SSF, it was also apparent that parameters measuring the complete feedstock are inadequate for explaining cellulose reactivity/hydrolyzability during saccharification. As a consequence of these conclusions, the final study focused on properties of model celluloses and initial rates of hydrolysis by the major cellulase - CBHI. The content of insoluble ends was measured by different modified soluble reducing sugar assays and by tritium labeling through NaB³H₄ reduction reactions. The content of insoluble reducing ends partially explained the relative initial rates of hydrolysis. However, comparisons between celluloses in their crystalline and corresponding amorphous state revealed that crystallinity also accounts for some of the observed rate differences. Furthermore, surface characteristics, such as the presence of pores, must be considered to fully explain cellulose reactivity.
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