Abstract
BackgroundWhole-tree chips will be a likely feedstock for future biorefineries because of their low cost. Non-structural components (NSC), however, represent a significant part of whole-tree chips. The NSC can account for more than 10% of whole-tree poplar mass when the trees are grown in short rotation cycles. The influence of NSC, however, on the production of fuels and chemicals is not well known. In this study, we assessed the impact of NSC removal from poplar whole-tree chips on pretreatment and enzymatic hydrolysis yields, overall sugar recovery, and fermentation yield. In addition, we evaluated the economics of preprocessing as a new unit operation in the biorefinery.ResultsPoplar whole-tree chips were preprocessed by neutral or acidic washing before steam pretreatment, enzymatic hydrolysis, and fermentation. Preprocessing of poplar reduced ash and extractives content as much as 70 and 50%, respectively. The overall sugar yield after pretreatment and hydrolysis was 18–22% higher when the biomass had been preprocessed, which was explained by higher sugar yields in liquid fraction and more efficient enzymatic hydrolysis of the solid fraction. The liquid fraction ethanol fermentation yield was 36–50% higher for the preprocessed biomass.ConclusionsIt appears that preprocessing reduced the buffering capacity of the biomass due to ash removal, and thereby improved the enzymatic hydrolysis. Removal of extractives during preprocessing improved the fermentation yield. The economic modeling shows that a preprocessing unit could have significant economic benefits in a biorefinery, where poplar whole-tree chips are used as bioconversion feedstock.
Highlights
Whole-tree chips will be a likely feedstock for future biorefineries because of their low cost
Whole-tree poplar chips were preprocessed in three different ways before steam explosion, enzymatic hydrolysis, and fermentation
The overall monomeric sugar yields, sugar recoveries, and ethanol yields were used to evaluate the impact of preprocessing on the steam pretreatment and subsequent enzymatic hydrolysis and fermentation
Summary
Whole-tree chips will be a likely feedstock for future biorefineries because of their low cost. There has been relatively less research, on the role of biomass non-structural components (NSC) on bioconversion to fuels and chemicals. Known as physiological ashes, are minerals bound within the cells and cell walls. They are incorporated into the lignocellulosic structure and are resistant to washing [7, 8]. These types of ash are feedstock specific and are governed by the physiology of the plants, growth stages, and growing conditions. Ash accounts for only 1.3% of the stem wood for short rotation coppice poplar, but branches, bark, and leaves contain higher level of inorganics of 5.7, 6.9, and 10.5%, respectively [10]
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