Dilute sulfuric acid pretreatment of corn stover at high solids concentrations
The enzymatic digestibility of a pretreated substrate is enhanced by increasing the severity of the pretreatment conditions, apparently because a greater fraction of the hemicellulose sheath surrounding the cellulose is dissolved. This allows the enzyme greater access to the cellulose. However, optimizing enzymatic digestibility will not optimize the production of ethanol. Although increasing the severity of the pretreatment conditions will decrease the remaining xylan, it will also result in the conversion of xylose to furfural. This is a loss of a potential carbon source for conversion to ethanol. The more severe conditions also result in the conversion of more of the cellulose to glucose and subsequent conversion to 5-hydroxymethylfurfural (HMF). Although the digestibility of the pretreated material may be enhanced by the more severe conditions, the conversion of this material to ethanol by yeast may be poor because of the higher levels of furfural and HMF, which are toxic to yeast. The best pretreatment conditions are those that produce the highest ethanol yields, which is influenced by the enzymatic digestibility of the pretreated substrate, the xylose yield, and the production of toxic byproducts.
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