Comparison of Dilute Acid and Sulfite Pretreatments onAcacia confusafor Biofuel Application and the Influence of Its Extractives

Abstract

Chemical components of lignocellulosic biomass may impede biofuel processing efficiency. To understand whether the heartwood of Acacia confusa is suitable for biofuel application, extractive-free heartwood of A. confusa was subjected to dilute acid (DA) or sulfite pretreatments. Sugar recoveries were used to evaluate the performance of different pretreatments. Cell wall properties, such as 4-O-alkylated lignin structures, S/G ratios, and xylan contents, of the pretreated samples showed significant correlations with the enzymatic saccharification of glucan. The 4% bisulfite-pretreated samples produced higher total sugar recoveries than DA-treated samples. The highest total sugar recoveries from DA and sulfite pretreatment were 52.0% (170 °C for 20 min) and 65.3% (4% NaHSO3 and 1% H2SO4), respectively. The results also demonstrated that the existence of extractives in the heartwood of A. confusa hindered the sugar recoveries from both the pretreatments and enzymatic saccharification. Total sugar recoveries were reduced 11.7-17.7% in heartwood samples with extractives.

Can we use short rotation coppice poplar for sugar based biorefinery feedstock? Bioconversion of 2-year-old poplar grown as short rotation coppice

“…Consequently, the presence of leaf increased the non-carbohydrate constituent and reduced the proportion of convertible sugar in WTC. Additionally, high phenolic content, ash, and extractives in the leaves will have negative impacts on the bioconversion process [39–42]. The leaves appeared to be problematic.…”

Current Understanding of the Correlation of Lignin Structure with Biomass Recalcitrance

“…An unclear correlation has also been reported, such as green liquor and Kraft pretreated Eucalyptus (Papa et al, 2012; Santos et al, 2012), NaOH and H 2 SO 4 pretreated wheat and rice samples (Wu et al, 2013), and mild acid treated maize cell wall (Zhang et al, 2011). When the S/G ratio of the remaining lignin in pretreated biomass is studied, contradictory results also exist: a lesser proportion of non-condensed lignin in the pretreated biomass was reported to be beneficial to biomass hydrolysis as non-condensed lignin (high β- O -4′) tended to be linear shape, likely a higher coverage over cellulose fibers (Zhang et al, 2011; Yeh et al, 2014); by contrast, others found high S/G ratio of lignin in the pretreated biomass was positively correlated with enzymatic digestibility as branched G-lignin gave rise to more physical barrier (Santos et al, 2012; Yu et al, 2014). These inconsistent results suggest that S/G ratio contributes only partially to biomass recalcitrance, and the complexities of biomass species and pretreatment with concomitant other cell wall structure changes likely shelter the effects arising from lignin composition.…”

Performance of three delignifying pretreatments on hardwoods: hydrolysis yields, comprehensive mass balances, and lignin properties

“…For the Cu-AHP, this is manifested as slightly lower yields for the eucalyptus at low enzyme loadings and shorter hydrolysis times, although the maximum glucose yields (~ 80%) are comparable at the highest enzyme loadings (30 mg/g) and incubation times (72 h). A likely contributor to this higher recalcitrance in the eucalyptus is the higher lignin content (30% by mass) relative to the poplar (24% by mass) as well as potentially the higher extractives content, which are known to inhibit cellulase activity [48] and decrease the efficacy of pretreatment and enzymatic hydrolysis [49]. When similar conditions are compared for the [Ch] [Lys] pretreatment, the poplar gives higher yields for most conditions, presumably due to a combination of the lower intrinsic recalcitrance of the biomass as well as the (unquantified) pretreatment-solubilized inhibitors of hydrolysis.…”