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The reductive catalytic fractionation (RCF) of lignocellulosic biomass is an attractive method for the conversion of lignin toward valuable low‐molecular weight aromatics. A limitation to the upscaling of such technology is represented by the use ofpressurized hydrogen gas. Here, the role of hydrogen gas within the RCF of wheat straw biomass is investigated. The use of H2 is shown to enhance lignin depolymerization, by virtue of an improved hydrogenolysis and hydrogenation of lignin fragments, with a yield of phenolic monomers that increased from ca. 12 wt % of acid‐insoluble lignin in the initial biomass under inert atmosphere to up to ca. 25 wt % under H2 (in methanol, at 250 °C, with Ru/C). The adoption of methanol, ethanol or isopropanol as hydrogen‐donor solvents was also investigated in the absence of H2. Ethanol was found to give the highest yield of monophenolic compounds (up to ≈20 wt %) owing to a better balance between solvolysis, hydrogenolysis, and hydrogenation of lignin. Nevertheless, a substantial loss of the carbohydrate fraction was observed. The use of a lower temperature (200 °C) in combination with H3PO4 resulted in an improved recovery of cellulose in the pulp and in the solubilization of hemicellulose and lignin, with the formation of monosaccharides (≈14 wt % of polysaccharides in the initial biomass) and phenolic monomers (up to 18 wt %, in the absence of H2). Overall, a tradeoff exists between the removal of H2 from the process and the production of low‐molecular weight phenolics during RCF. [ABSTRACT FROM AUTHOR]

Sodium dithionite is utilized as a reducing agent in the organosolv fractionation of lignocellulose to concomitantly produce cellulosic pulp and promote the reductive conversion of lignin into phenolic monomers. Reactions with model compounds highlight the role of sodium dithionite with respect to the reductive cleavage of β-O-4 bonds in lignin and the consequent formation of phenolic monomers. [ABSTRACT FROM AUTHOR]

Abstract: The main purpose of this study was pretreatment of prairie cordgrass obtaining three fractions: lignin, hemicellulose and fermentable cellulose. Modified clean fractionation process (using ethyl acetate–ethanol–water mixture) was employed to extract lignin and hemicellulose fractions. Different proportions of constituents in the solvent mixture were tested. In order to improve lignin recovery, the process was catalyzed with sulfuric acid. Optimization was performed for fractionation processing conditions using lignin recovery and glucose yields as primary response variables. Optimal conditions resulted in a 51.33% lignin recovery, 53.82% hydrolysis glucose yield and 33.73% xylose yield in the aqueous fraction. To improve cellulose digestibility, solid fraction was subjected to hydrothermal post-treatment, for which optimal processing conditions were found, resulting in 78.93% hydrolysis glucose yield. This research represents a step forward for biomass pretreatment, and may open up new possibilities for utilization of prairie cordgrass. [Copyright &y& Elsevier]

Abstract: Lignin extracted from prairie cordgrass, switchgrass, and corn stover (using ethyl acetate–ethanol–water organosolv pretreatment) was analyzed and characterized using several methods. These methods included analysis of purity (by determination of Klason lignin, carbohydrate, and ash contents), solubility (with several organic solvents), phenolic group analysis (ultraviolet ionization difference spectra, and nitrobenzene oxidation), and general functional group analysis (by 1H NMR). Results showed that all the examined lignin samples were relatively pure (contained over 50% Klason lignin, less than 5% carbohydrate contamination, and less than 3% ash), but switchgrass-derived lignin was observed to be the purest. All the lignins were found to contain high amounts of phenolic groups, while switchgrass-derived lignin was the most phenolic, according to the ionization difference spectra. Nitrobenzene oxidation revealed that all the lignin samples contained available guaiacyl units in high amounts. [Copyright &y& Elsevier]

In this study, modified clean fractionation process was optimized for prairie cordgrass, with usage of alternative organic constituent - ethyl acetate. Other constituents of the solvent mixture included ethanol and water. Clean fractionation solvent was used in different proportions of the constituents. Process efficiency was determined by lignin recovery, solvent composition, as well as time and temperature applied to each sequential process. Glucose yield during enzymatic hydrolysis and overall pretreatment were calculated. Optimal conditions (125°C, 37 min, with the solvent composition of ester:ethanol:water = 32.5:22.5:45) yielded a 20% lignin recovery, 38% glucose yield during enzymatic hydrolysis and 26% xylose recovery in aqueous fraction. [ABSTRACT FROM AUTHOR]

• The process promoted by Na 2 S 2 O 4 boosts lignin depolymerization and formation of monophenolics. • Higher temperature and longer reaction time favored lignin and hemicellulose extraction. • The combination of n -butanol and water improved lignin extraction and depolymerization. • The process was effective for treating lignocellulose from various biomass sources. • A techno-economic assessment highlights potential economic viability of the upgrading process. The development of biomass pretreatment approaches that, next to (hemi)cellulose valorization, aim at the conversion of lignin to chemicals is essential for the long-term success of a biorefinery. Herein, we discuss a dithionite-assisted organosolv fractionation (DAOF) of lignocellulose in n -butanol and water to produce cellulosic pulp and mono-/oligo-aromatics. The study frames the technicalities of this biorefinery process and relates them to the features of the obtained product streams. We comprehensively identify and quantify all products of interest: solid pulp (acid hydrolysis-HPLC, ATR-FTIR, XRD, SEM, enzymatic hydrolysis-HPLC), lignin derivatives (GPC, GC–MS/FID, 1H–13C HSQC NMR, ICP-AES), and carbohydrate derivatives (HPLC). These results were used for inspecting the economic feasibility of DAOF. In the best process configuration, a high yield of monophenolics was reached (∼20 wt%, based on acid insoluble lignin in birch sawdust). Various other lignocellulosic feedstocks were also explored, showing that DAOF is particularly effective on hardwood and herbaceous biomass. Overall, this study demonstrates that DAOF is a viable fractionation method for the sustainable upgrading of lignocellulosic biomass. [ABSTRACT FROM AUTHOR]