The choices that are made with respect to the efficient development and operation of any bioenergy conversion process are inherently linked to the physical and chemical properties of the feedstock. These interactions can be examined at a variety of scales ranging from the landscape scale where the availability of feedstock can affect the appropriate energy generation method for a given region, to the molecular scale where small variations in cell wall components can have a large impact on process yields. Because biomass is an inherently heterogeneous material, it is necessary to develop a broad understanding of how different characteristics impact the conversion process: how differences in biomass classification can help us make generalizations about new feedstocks, whether different varieties of the same species have inherent differences that alter their relative efficiencies of conversion, and what variations are possible depending on which portion of the plant is used for a feedstock.At the landscape scale, the distribution of usable crop residues would be one factor influencing the decision of where to locate a lignocellulosic biorefinery. In Mainland China, 594 million metric tons of crop residues are produced each year, however only 125 million tons are available for energy generation, either in rural homes or in a larger facility. Based on residue availability, Henan in particular would be the most likely site for a biorefinery, with potential for other locations in central, eastern, and northeastern China. Plant materials can interact with pretreatment and enzymatic hydrolysis at a variety of scales. Plant classification largely determines cell wall chemistry, and there are distinct differences between the way that dicots and grasses interact with pretreatment and enzymatic hydrolysis. Mixed-species feedstocks that have a higher mass contribution by grasses are more digestible and also generate higher sugar yields compared to those dominated by dicots. In contrast, the differences between different varieties of the same species, in this case switchgrass (when grown under the same environmental conditions), showed much smaller differences in digestibility, optimal pretreatment conditions, and enzyme combinations. At the next scale down, the different portions of the plant also have distinctly different structures and compositions that affect their amenability toward pretreatment. This could be one consideration toward determining how to best harvest lignocellulosics on the field. For corn stover, the best scenario involved harvesting the fractions in order of decreasing lignin content: husk > leaves > stem > cob, an order that is feasible using currently available harvesting equipment and methods. Klason lignin content was related to decreased glucan digestibility in both the mixed-species materials and in corn stover fractions. However, no effect due to lignin content or lignin monomer composition was observed for genetically modified poplar. Of the samples tested, the C4H::F5H poplar that was modified to have highly linear and extractable lignin with mostly syringyl residues showed the greatest improvement following AFEXTM pretreatment. However the increase was not substantial and for these types of materials it may be more effective to employ an liquid ammonia pretreatment that is able to extract the lignin and simultaneously modify the cellulose crystal structure.
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