The impact of lignin‐derived inhibition on enzymatic hydrolysis is investigated by using lignins isolated from untreated woods and pretreated wood pulps. A new method, biomass reconstruction, for ...which isolated lignins are precipitated onto bleached pulps to mimic lignocellulosic biomass, is introduced, for the first time, to decouple the lignin distribution issue from lignin chemistry. Isolated lignins are physically mixed and reconstructed with bleached pulps. Lignins obtained from pretreated woods adsorb two to six times more cellulase than lignins obtained from untreated woods. The higher adsorption of enzymes on lignin correlates with decreased carbohydrate conversion in enzymatic hydrolysis. In addition, the reconstructed softwood substrate has a lower carbohydrate conversion than the reconstructed hardwood substrate. The degree of condensation of lignin increases significantly after pretreatment, especially with softwood lignins. In this study, the degree of condensation of lignin (0.02 to 0.64) and total OH groups in lignin (1.7 to 1.1) have a critical impact on cellulase adsorption (9 to 70 %) and enzymatic hydrolysis (83.2 to 58.2 %); this may provide insights into the more recalcitrant nature of softwood substrates.
Breaking it down: A new method called biomass reconstruction is introduced to study the effect of lignin chemistry on enzymatic hydrolysis. Hydrolysis is inhibited by increasing degree of condensation and decreasing total hydroxyl content of lignin; this may be a reason for the high recalcitrant nature of softwood substrate.
Biphenyl linkage is the second most abundant linkage in softwood lignin; the β-O-4′ linkage being the most abundant linkage. That about 20-28% of monolignols are linked by biphenyl linkage has been ...demonstrated by UV spectroscopy, permanganate oxidation,
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C NMR, and thioacidolysis followed by
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P NMR. Most, if not all, of the biphenyl structures in softwood lignin are etherified, indicating that biphenyl structures are formed while monolignols are being transported to the lignifying zone during lignin biosynthesis. Along with 4-O-5′ (∼3/100 C9 units), β-6′/α-6′ (∼3/100 C9) and noncyclic α-O-4′ structures (4/100 C9), biphenyl structures are the major branching points of lignin structure. Thus, at least one out of every three C9 units in softwood lignin are branching units. This fact indicates that softwood lignin is most likely a network polymer. Many alkyl-aryl ether bonds are cleaved during ball milling for the isolation of Milled Wood Lignin (MWL), but the number of branching points remains the same. Therefore, softwood milled wood lignin, with a number average DP of 20, exists most likely as at least a highly branched polymer and unlikely as a linear polymer. Harwood lignin has less biphenyl structures (∼9%), but has more 4-O-5′ (∼7%), noncyclic α-O-4′ (6%) and similar β-6′/α-6′ (∼2%) linkages as compared with softwood lignin. Thus, only one out of every four C9 units is a branching point, indicating that hardwood lignin is most likely a highly branched polymer. Hardwood MWL is most likely a branched polymer, but one cannot rule out the chance of finding a few linear oligomers in MWL. One potential branching point is not considered in the above discussion. The lignin-carbohydrate complexes are also branching points in lignin. The number of LCC linkages in native lignin cannot be determined precisely.
A multi-omics quantitative integrative analysis of lignin biosynthesis can advance the strategic engineering of wood for timber, pulp, and biofuels. Lignin is polymerized from three monomers ...(monolignols) produced by a grid-like pathway. The pathway in wood formation of Populus trichocarpa has at least 21 genes, encoding enzymes that mediate 37 reactions on 24 metabolites, leading to lignin and affecting wood properties. We perturb these 21 pathway genes and integrate transcriptomic, proteomic, fluxomic and phenomic data from 221 lines selected from ~2000 transgenics (6-month-old). The integrative analysis estimates how changing expression of pathway gene or gene combination affects protein abundance, metabolic-flux, metabolite concentrations, and 25 wood traits, including lignin, tree-growth, density, strength, and saccharification. The analysis then predicts improvements in any of these 25 traits individually or in combinations, through engineering expression of specific monolignol genes. The analysis may lead to greater understanding of other pathways for improved growth and adaptation.
Changes to the molecular properties of lignin over the course of biorefinery processing were investigated by using sweetgum as a feedstock. Hydrothermal pretreatment has been used because it is an ...economically attractive, green process. Three representative biorefinery lignin preparations were obtained, with about 70 % yield based on raw lignin. The three fractions included soluble lignin adsorbed on resin (XADL), solvent‐extracted lignin (HTCELp), and an additional ball‐milled residual lignin (HTRELp). By comparing the raw and biorefinery lignin preparations, it can be concluded that lignin undergoes both degradation and condensation throughout the various stages of the hydrothermal‐based biorefinery process. The two fractions made soluble by biorefinery processing, XADL and HTCELp, were found to be low‐molecular‐weight degradation products enriched with free phenolic hydroxyl groups. In addition, about 15 % of noncondensed phenolic units were involved in condensation reactions. Quantitative NMR spectroscopy analysis revealed that at least about 28 % of β‐O‐4′ substructures were cleaved. Hibbert's ketones were identified in XADL and HTRELp, which provided evidence of lignin undergoing acidolysis. The contents of β‐5′ and β‐β′ did not change significantly upon biorefinery processing. Finally, episyringaresinol was detected in XADL and HTCELp. It is hoped that these findings will help to further demonstrate the specific effects of biorefinery processing on lignin in hardwood and facilitate its utilization to improve biorefinery economics.
Part of the process: Hydrothermal pretreatment is used because it is an economically attractive, green process. Changes to the molecular properties of lignin over the course of biorefinery processing are investigated by using sweetgum as a feedstock. By comparing the raw and biorefinery lignin preparations, it is seen that lignin undergoes both degradation and condensation during various stages of the hydrothermal‐based biorefinery process.
A quantitative approach to characterize lignin—carbohydrate complex (LCC) linkages using a combination of quantitative 13C NMR and HSQC 2D NMR techniques has been developed. Crude milled wood lignin ...(MWLc), LCC extracted from MWLc with acetic acid (LCC-AcOH) and cellulolytic enzyme lignin (CEL) preparations were isolated from loblolly pine (Pinus taeda) and white birch (Betula pendula) woods and characterized using this methodology on a routine 300 MHz NMR spectrometer and on a 950 MHz spectrometer equipped with a cryogenic probe. Structural variations in the pine and birch LCC preparations of different types (MWL, CEL and LCC-AcOH) were elucidated. The use of the high field NMR spectrometer equipped with the cryogenic probe resulted in a remarkable improvement in the resolution of the LCC signals and, therefore, is of primary importance for an accurate quantification of LCC linkages. The preparations investigated showed the presence of different amounts of benzyl ether, γ-ester and phenyl glycoside LCC bonds. Benzyl ester moieties were not detected. Pine LCC-AcOH and birch MWLc preparations were preferable for the analysis of phenyl glycoside and ester LCC linkages in pine and birch, correspondingly, whereas CEL preparations were the best to study benzyl ether LCC structures. The data obtained indicate that pinewood contains higher amounts of benzyl ether LCC linkages, but lower amounts of phenyl glycoside and γ-ester LCC moieties as compared to birch wood.
A novel carbon solid acid catalyst was synthesized by the sulfonation of carbonaceous material which was prepared by carbonization of sucrose using 4-BDS as a sulfonating agent. TEM, N2 ...adsorption-desorption, elemental analysis, XPS and FT-IR were used to characterize the catalyst. Then, the catalyst was applied for the conversion of xylose and corn stalk into furfural in GVL. The influence of the reaction time, temperature and dosage of catalyst on xylose dehydration were also investigated. The Brønsted acid catalyst exhibited high activity in the dehydration of xylose, with a high furfural yield of 78.5% at 170°C in 30min. What's more, a 60.6% furfural yield from corn stalk was achieved in 100min at 200°C. The recyclability of the sulfonated carbon catalyst was perfect, and it could be reused for 5times without the loss of furfural yields.
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•Vapor-releasing method allows furfural to be easily separated from by-products.•The furfural yield of 73% was achieved in aqueous system without a catalyst.•Organic acids from ...hydrolysate works as catalysts for furfural production.•No purification of biomass hydrolysate is necessary for furfural production.
Biomass hydrolysate from autohydrolysis pretreatment was used for furfural production considering it is in rich of xylose, xylo-oligomers, and other decomposition products from hemicellulose structure. By using the vapor-releasing reactor system, furfural was protected from degradation by separating it from the reaction media. The maximum furfural yield of 73% was achieved at 200 °C for biomass hydrolysate without the use of the catalyst. This is because the presence of organic acids such as acetic acid in hydrolysate functioned as a catalyst. According to the results in this study, biomass hydrolysate with a vapor-releasing system proves to be efficient for furfural production. The biorefinery process which allows the separation of xylose-rich autohydrolysate from other parts from biomass feedstock also improves the overall application of the biomass.
► Both lignin content and delignification method affect enzymatic hydrolysis. ► Sodium chlorite delignification effectively improves the digestibility of softwood. ► Delignification increases ...accessible pore volume in biomass. ► Hydrolysis levels off at 15% lignin content, which correspond 0.30g/g pore volume.
The effect of delignification methods on enzymatic hydrolysis of forest biomass was investigated using softwood and hardwood that were pretreated at an alkaline condition followed by sodium chlorite or ozone delignification. Both delignifications improved enzymatic hydrolysis especially for softwood, while pretreatment alone was found effective for hardwood. High enzymatic conversion was achieved by sodium chlorite delignification when the lignin content was reduced to 15%, which is corresponding to 0.30–0.35g/g accessible pore volume, and further delignification showed a marginal effect. Sample crystallinity index increased with lignin removal, but it did not show a correlation with the overall carbohydrate conversion of enzymatic hydrolysis.
Phenolation can be used to improve the reactivity and decrease the molecular weight of lignin, thereby making it more useful for various applications. We report an effective phenolation process with ...only a catalytic amount of sulfuric acid and using phenol as solvent. The optimum phenolation conditions for pine kraft lignin and sweetgum biorefinery lignin were determined to be lignin/phenol (L/P, wt/wt) of 3/5, 5% acid charge at 90 °C for 2 h and L/P of 2/5, 5% acid charge at 110 °C for 2 h, respectively. Phenolation resulted in introducing 30 wt % of phenol onto pine kraft lignin and 60 wt % of phenol onto sweetgum biorefinery lignin and significantly decreasing in the molecular weight of lignin. Phenol was incorporated onto both the side chains and aromatic nuclei of lignin. All lignin substructures of β-O-4′, β-5′/α-O-4′, β–β′, α-carbonyl, etc. were reacted, resulting in a significant decrease in aliphatic hydroxyl groups and increase in the phenolic hydroxyl groups. The comprehensive characterization revealed that most of the ethers linkages were cleaved during phenolation. The β-elimination of the γ-hydroxymethyl group as formaldehyde was the main reaction of side chains. The released formaldehyde reacted with phenol and lignin to form diphenylmethanes. Plausible mechanisms for lignin phenolation are also discussed.
Biomass derived 5-hydroxymethylfurfural (HMF) is regarded as an important platform molecule for the synthesis of value-added chemicals and fuels, but the high production cost has always been a ...bottleneck for the industrial scale use of HMF. Different mineral acids (HCl and H 2 SO 4 ) being used as the catalyst and different salts being used as the reaction promoter were evaluated. It was found that HCl, in combination with NaCl, in a water/γ-valerolactone system showed high selectivity and impressive efficiency for the synthesis of HMF from glucose. The optimal conditions to obtain the best HMF yield (62.45%) were 0.2 M HCl and 0.1 M NaCl at 140 °C with a residence time of 60 minutes. An 18.22% molar yield of LA was obtained as a by-product. The effect of different anions was also investigated, and it was determined that not only the hydrogen ions, but also the nature of the acid and the type of salt played a joint role in improving the HMF yield. In addition, a possible synthesis pathway was proposed for large scale production of HMF.
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