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  1. Sequential organosolv fragmentation approach (SOFA) enhances the self-assembling process of high-quality lignin nanoparticles (LNPs) by tailoring the lignin chemistry in biorefineries.
  2. Cell wall recalcitrance is the major obstacle for plant biomass conversion to biofuels.
  3. Sustainable biorefinery heavily depends on the generation of value-added products, particularly from lignin. Despite considerable efforts, the production of fungible lignin bioproducts is still hindered by the poor fractionation and low reactivity of lignin. To address these challenges, the sequential organosolv fragmentation approach (SOFA) using ethanol plus different-stage catalysts was explored to selectively dissolve lignin for producing multiple uniform lignin streams, and to tailor its chemistry and reactivity for fabricating lignin nanoparticles (LNPs) with desired quality features. In a biorefinery concept, the carbohydrate output is taken into consideration. SOFA significantly increased the glucose and xylose yields, suggesting an improved monomer-sugarmore » release. The fractionated lignin was used to fabricate LNPs via self-assembly. Although these LNPs were derived from the same substrate, they exhibited different properties. The effective diameter almost followed the order of stage 1, stage 3, and stage 2 in each SOFA, and the smallest effective diameter was approximately 130 nm from SOFA using ethanol plus sulfuric acid. The polydispersity index and zeta potential were less than 0.08 and –50 mV, respectively, suggesting good uniformity and stability of the LNPs. Lignin characterization results suggested that SOFA using ethanol plus sulfuric acid produced high-molecular-weight lignin, decreased S/G ratio, and β-O-4 and β–β linkage abundance, yet produced the condensed lignin and enhanced its hydrophobicity. More importantly, it exposed more phenolic OH groups and enhanced the stability of LNPs, likely due to the hydrogen bond networks. Together with enriched COOH groups, it promoted the formation of electrical double layers and increased the zeta potential of LNPs. In conclusion, by tailoring the lignin chemistry using SOFA to enhance the self-assembling process, high-quality LNPs of a spherical shape, small effective diameters, and good stability have been fabricated, which represents a sustainable means for upgrading the low-value lignin and thus contributes to the profitability of biorefineries.« less
  4. We present that growing energy demand and the need to reduce environmental impact, increase energy security, and rural economic development has encouraged the development of sustainable renewable fuels. Non-food lignocellulosic biomass is a suitable source for sustainable energy because the biomass feedstocks are low cost, abundant, and carbon neutral. Recent thermochemical conversion studies are frequently directed at converting biomass to high quality liquid fuel precursors or chemicals in a single step. Supercritical ethanol has been selected as a promising solvent medium to deconstruct lignocellulosic biomass since the ethanol has extraordinary solubility towards lignocellulosic biomass and can be resourced from cellulosicmore » ethanol facilities. This review provides critical insight into both catalytic and non-catalytic strategies of lignocellulose deconstruction. In this context, the supercritical ethanol deconstruction pathways are thoroughly reviewed; gas chromatography coupled with mass spectrometry (GC-MS), one-dimensional and two-dimensional nuclear magnetic resonance spectrometry (NMR), and elemental analysis strategies towards liquid biomass deconstruction products are critically presented. Lastly, this review aims to provide readers a broad and accurate roadmap of this novel biomass to biofuel conversion techniques.« less
  5. This study demonstrates the effect of lignin source on the structural and electrochemical properties of lignin-derived carbon materials.
  6. Valorization of lignin to high-value chemicals and products along with biofuel production is generally acknowledged as a technology platform that could significantly improve the economic viability of biorefinery operations. With a growing demand for electrical energy storage materials, lignin-derived activated carbon (AC) materials have received increasing attention in recent years. However, there is an apparent gap in our understanding of the impact of the lignin precursors (i.e., lignin structure, composition and inter-unit linkages) on the structural and electrochemical properties of the derived ACs. In the present study, lignin-derived ACs were prepared under identical conditions from two different lignin sources: alkalinemore » pretreated poplar and pine. The lignin precursors were characterized using composition analysis, size exclusion chromatography, and 2D HSQC nuclear magnetic resonance (NMR). Distinctive distributions of numerous micro-, meso- and macro-porous channels were observed in the two lignin-derived ACs. Poplar lignin-derived ACs exhibited a larger BET surface area and total mesopore volume than pine lignin-derived AC, which contributed to a larger electrochemical capacitance over a range of scan rates. X-ray photoelectron spectroscopic analysis (XPS) results revealed the presence of oxygen-containing functional groups in all lignin-derived ACs, which participated in redox reactions and thus contributed to an additional pseudo-capacitance. A possible process mechanism was proposed to explain the effects of lignin structure and composition on lignin-derived AC pore structure during thermochemical conversion. As a result, this study provides insight into how the lignin composition and structure affect the derived ACs for energy storage applications.« less
  7. Use of oleaginous microorganisms as “micro-factories” for accumulation of single cell oils for biofuel production has increased significantly to mitigate growing energy demands, resulting in efforts to upgrade industrial waste, such as second-generation lignocellulosic residues, into potential feedstocks. Dilute-acid pretreatment (DAP) is commonly used to alter the physicochemical properties of lignocellulosic materials and is typically coupled with simultaneous saccharification and fermentation (SSF) for conversion of sugars into ethanol. The resulting DAP residues are usually processed as a waste stream, e.g. burned for power, but this provides minimal value. Alternatively, these wastes can be utilized as feedstock to generate lipids, whichmore » can be converted to biofuel. DAP-SSF residues were generated from pine, poplar, and switchgrass. High performance liquid chromatography revealed less than 0.13% monomeric sugars in the dry residue. Fourier transform infrared spectroscopy was indicative of the presence of lignin and polysaccharides. Gel permeation chromatography suggested the bacterial strains preferred molecules with molecular weight ~ 400–500 g/mol. DAP-SSF residues were used as the sole carbon source for lipid production by Rhodococcus opacus DSM 1069 and PD630 in batch fermentations. Depending on the strain of Rhodococcus employed, 9–11 lipids for PD630 and DSM 1069 were observed, at a final concentration of ~ 15 mg/L fatty acid methyl esters (FAME) detected. Though the DAP-SSF substrate resulted in low FAME titers, novel analysis of solid-state fermentations was investigated, which determined that DAP-SSF residues could be a viable feedstock for lipid generation.« less
  8. The formation of lignin-like structures by the degradation primarily of plant polysaccharides has been observed after the severe thermochemical acidic pretreatment of lignocellulosic biomass.
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  9. Background: Cellulase adsorption to lignin is considered a cost barrier for bioethanol production; however, its detailed association mechanism is still not fully understood. In this study, two natural poplar variants with high and low sugar release performance were selected as the low and high recalcitrant raw materials (named L and H, respectively). Three different lignin fractions were extracted using ethanol, followed by p-dioxane and then cellulase treatment from the dilute acid pretreated poplar solids (fraction 1, 2, and 3, respectively).Results: Each lignin fraction had different physicochemical properties. Ethanol-extracted lignin had the lowest weight average molecular weight, while the molecular weightsmore » for the other two lignin fractions were similar. 31P NMR analysis revealed that lignin fraction with higher molecular weight contained more aliphatic hydroxyl groups and less phenolic hydroxyl groups. Semi-quantitative analysis by 2D HSQC NMR indicated that the lignin fractions isolated from the natural variants had different contents of syringyl (S), guaiacyl (G) and interunit linkages. Lignin extracted by ethanol contained the largest amount of S units, the smallest amounts of G and p-hydroxybenzoate (PB) subunits, while the contents of these lignin subunits in the other two lignin fractions were similar. The lignin fraction obtained after cellulase treatment was primarily comprised of β-O-4 linkages with small amounts of β-5 and β–β linkages. The binding strength of these three lignin fractions obtained by Langmuir equations were in the order of L1 > L3 > L2 for the low recalcitrance poplar and H1 > H2 > H3 for the high recalcitrance poplar.Conclusions: Overall, adsorption ability of lignin was correlated with the sugar release of poplar. Structural features of lignin were associated with its binding to CBH. For natural poplar variants, lignin fractions with lower molecular weight and polydispersity index (PDI) exhibited more CBH adsorption ability. Lignins with more phenolic hydroxyl groups had higher CBH binding strength. It was also found that lignin fractions with more condensed aromatics adsorbed more CBH likely attributed to stronger hydrophobic interactions.« less

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