Plant Cell Walls: Basics of Structure, Chemistry, Accessibility and the Influence on Conversion

This book is focused on the pretreatment of plant biomass, a necessary step for efficient conversion of plant cell-wall materials to liquid transportation fuels and other products. Pretreatment is required because it is difficult to access, separate, and hydrolyze monomeric sugars from biopolymers within biomass. Accessible sugars can be further upgraded to products through chemical processes such as aqueous phase reforming or biological routes such as fermentation of the sugars to ethanol. This resistance to degradation or difficulty to release the monomers (mostly sugars) is commonly referred to as recalcitrance [1]. Many methods can be employed to overcome recalcitrance, but the underlying cause of recalcitrance lies in the complex combination and diversity of chemical and structural features of the plant cell walls. Recent studies by Perlack et al. [2,3] estimated that there is approximately 1.4 billion tons of biomass available annually in the United States, which could replace up to one-third of the petroleum-derived fuels currently used. This study determined that 1 billion tons from agricultural lands and an additional 368 million dry tons from forest lands could be sustainably harvested annually. The types and amounts of biomass available for conversion to biomass-derived fuels, whether agricultural residues, forest residues, or purposegrown energy crops such as switchgrass, willow or poplar, is dependent on geography and climate, as shown in Figure 3.1.