Removal of non-structural components from poplar whole-tree chips to enhance hydrolysis and fermentation performance

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.

Novel ethanol production using biomass preprocessing to increase ethanol yield and reduce overall costs

“…These ndings are consistent with the literature, where Hӧrhammer et al (17) reports 59% ash removal from poplar WTC using an acidic-neutral wash, and He et al (6) reporter 20% ash removal after neutral washing of corn stover. Interestingly, alkaline preprocessed CPC biomass showed an approximate 40% increase in total ash content when compared to untreated CPC.…”

“…Similar results were reported by Hӧrhammer et al (17), where acidic-neutral and neutral washes removed 43% and 51%…”

“…Once the pH of all samples was stable, it was noted that all preprocessing conditions were able to reduce the buffering capacity of the biomass and achieve a lower pH than untreated biomass. Hörhammer et al had similar results where acidic and neutral preprocessing decreased the buffering capacity of 2year-old poplar whole-tree chips when compared to untreated biomass due to a lower ash content (17). The CPC samples presented similar trends as the WTC, as it is shown in Figure 1b.…”

“…Preprocessing, however, has also been proposed as a method to remove other types of NSC, such as acetic acid and extractives. Previous work from our research group found that dilute-acid preprocessing of poplar WTC resulted in higher monomeric sugar yield in the liquid fraction after pretreatment, improved cellulose digestibility during enzymatic hydrolysis, and increased ethanol fermentation yield from 5% to 55% due to the removal of NSCs during preprocessing (17). Similarly, Castro et al investigated the effects of alkaline deacetylation on…”

“…Economic analyses reported by previous studies suggested the use of recycled process water for the washing step to make it more cost-effective (17,19).…”