Effective Biomass Fractionation through Oxygen-Enhanced Alkaline–Oxidative Pretreatment

Abstract

The high recalcitrance of plant cell walls is an obstacle for effective chemical or biological conversion into renewable chemicals and transportation fuels. Here, we investigated the utilization of both oxygen (O2) and hydrogen peroxide (H2O2) as co-oxidants during alkaline–oxidative pretreatment to improve biomass fractionation and increase enzymatic digestibility. The oxidative pretreatment of hybrid poplar was studied over a variety of conditions. Employing O2 in addition to H2O2 as a co-oxidant during the two-stage alkaline pre-extraction/copper-catalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment process resulted in a substantial improvement in delignification relative to using H2O2 alone during the second-stage Cu-AHP pretreatment, leading to high overall sugar yields even at H2O2 loadings as low as 2% (w/w of the original biomass). The presence of H2O2, however, was both critical and synergistic. Performing analogous reactions in the absence of H2O2 resulted in approximately 25% less delignification and 30% decrease in sugar yields. The lignin isolated from this dual oxidant second stage had high aliphatic hydroxyl group content and reactivity to isocyanate, indicating that it is a promising substrate for the production of polyurethanes. To test the suitability of the isolated lignin as a source of aromatic monomers, the lignin was subjected to a sequential Bobbitt’s salt oxidation followed by a formic acid-catalyzed depolymerization process. Monomer yields of approximately 17% (w/w) were obtained, and the difference in yields was not significant between lignin isolated from our Cu-AHP process with and without O2 as a co-oxidant. Thus, the addition of O2 did not lead to significant lignin crosslinking, a result consistent with the two-dimensional heteronuclear single-quantum coherence NMR spectra of the isolated lignin.

Advances in Pretreatment of Straw Biomass for Sugar Production

“…Novel oxidative treatment technology of straw biomass fractionation has been reported, which applies both O 2 and H 2 O 2 as co-oxidants under alkaline conditions to simultaneously elevate the efficiency of straw biomass being converted into fermentable sugars and enhance the purity and stability of lignin ( Yuan et al, 2021 ).…”

Technoeconomic Evaluation of Recent Process Improvements in Production of Sugar and High-Value Lignin Co-Products via Two-Stage Cu-Catalyzed Alkaline-Oxidative Pretreatment

“…1). All models were based on experimental results for pretreatment process performance (biomass compositions and response to pretreatment and enzymatic hydrolysis) that were published previously [23].…”

“…charkoviensis×caudina cv. NE-19) with a composition of 45.5% glucan, 15.8% combined xylan, galactan, and mannan, 22.3% Klason lignin, 2.5% acid-soluble lignin, and 0.85% ash [23]. Brie y, the harvested poplar was air-dried and debarked prior to delivery.…”

“…The two-stage pretreatment process was fully described in our earlier work [23]. Brie y, sodium hydroxide (NaOH) and the prepared biomass feedstock were mixed in the pretreatment reactor at 10% NaOH loading on biomass (w/w based on the dry weight of the biomass) and 10% (w/v) consistency at either 90°C or 120°C for 1 h. The chemical composition of the alkaline pre-extracted poplar biomass was based on previously determined values (Additional le 1: Table S1).…”

“…Importantly, this prior work also demonstrated that the recovered lignins are more suitable in co-product applications than other process-derived lignins (e.g., Kraft lignin). Firstly, we demonstrated that Cu-AHP lignins were suitable as an aromatic polyol in polyurethane resin applications and 30% more reactive with isocyanate than Kraft lignin (on the basis of equivalent aliphatic hydroxyl content) [23], making it an ideal aromatic polyol substitute in polyurethanes. Likewise, the lignins from this process could be depolymerized into potentially high-value aromatic monomers at high yields (>30%), which is signi cantly higher than yields achievable from many other process-derived lignins [16, [24][25][26].…”