Tetrahydro-2-furanmethanol pretreatment of eucalyptus to enhance cellulose enzymatic hydrolysis and to produce high-quality lignin

Efficient extraction of light-colored lignin from bamboo by p-toluenesulfonic acid assisted tetrahydrofurfuryl alcohol aqueous solution

Acidic hydrotropes exhibit effective performance in fractionating the constituents of lignocellulosic biomass owing to their amphiphilic characteristics. However, the requirement for excessively high concentrations may lead to the condensation and aggregation of lignin. In this case, bamboo was extracted with 70 % (w/v) tetrahydrofurfuryl alcohol (THFA) aqueous solution containing 5-20 % (w/v) p-toluenesulfonic acid (pTsOH) at 90-120 °C for 1-4 h. Results indicated that 91 % of lignin was efficiently removed from bamboo, with subsequent recovery of 73.5 % achieved through extraction with 10 % pTsOH at 110 °C for 4 h. Furthermore, the resulting lignin exhibited a relative content of β-O-4 bonds of 64.1 %, displayed a light color (L*: 70.48), boasted a purity of 99.64 %, and possessed a moderate molecular weight. These attributes position it as a valuable candidate in functional material production. The aqueous solution provides an ideal medium for efficient extraction of uncondensed, light-colored lignin, thereby furnishing insights for advancing the utilization.

Efficient Fast Fractionation of Biomass Using a Diol-Based Deep Eutectic Solvent for Facilitating Enzymatic Hydrolysis and Obtaining High-Quality Lignin

Current DES pretreatment is often performed under relatively severe conditions with high temperature, long time, and high DES usage. This work studied a short-time diol DES (deep eutectic solvent) pretreatment under mild conditions to fractionate the bamboo, facilitate enzymatic hydrolysis, and obtain high-quality lignin. At an optimized condition of 130 °C for only 10 min, lignin and xylan removal reached 61.34 % and 84.15 %, with residual glucan showing a ~90 % enzymatic hydrolysis yield. Equally important, the dissolved lignin could be readily recovered with 97.51 % yield, exhibiting 96.65 % β-O-4 preservation. The fractionation and lignin protection mechanisms were unveiled by XRD, FTIR, cellulose-DP, 2D HSQC NMR, 31 P NMR and GPC analysis. This study highlighted that short-time fractionation of bamboo can be achieved by a diol-based DES which is an ideal strategy to upgrade the lignocellulose biomass for high enzymatic hydrolysis yields and high-quality lignin stream.

Purification and enzymatic properties of a new thermostable endoglucanase from Aspergillus oryzae HML366

Aspergillus oryzae HML366 is a newly screened cellulase-producing strain. The endoglucanase HML ED1 from A. oryzae HML366 was quickly purified by a two-step method that combines ammonium sulfate precipitation and strong anion exchange column. SDS-PAGE electrophoresis indicated that the molecular weight of the enzyme was 68 kDa. The optimum temperature of the purified endoglucanase was 60 ℃ and the enzyme activity was stable below 70 ℃. The optimum pH was 6.5, and the enzyme activity was stable at pH between 4.5 and 9.0. The analysis indicated that additional Na⁺, K⁺, Ca²⁺, and Zn²⁺ reduced the catalytic ability of enzyme to the substrate, but Mn²⁺ enhanced its catalytic ability to the substrate.The Km and Vmax of the purified endoglucanase were 8.75 mg/mL and 60.24 μmol/min·mg, respectively. In this study, we report for the first time that A. oryzae HML366 can produce a heat-resistant and wide pH tolerant endoglucanase HML ED1, which has potential industrial application value in bioethanol, paper, food, textile, detergent, and pharmaceutical industries.

Advances in organosolv modified components occurring during the organosolv pretreatment of lignocellulosic biomass

The valorization of organosolv pretreatment (OP) is a required approach to the industrialization of the current enzyme-mediated lignocellulosic biorefinery. Recent literature has demonstrated that the solvolysis happening in the OP can modify the soluble components into value-added active compounds, namely organosolv modified lignin (OML) and organosolv modified sugars (OMSs), in addition to protecting them against excessive degradation. Among them, the OML is coincidental with the "lignin-first" strategy that should render a highly reactive lignin enriched with β-O-4 linkages and less condensed structure by organosolv grafting, which is desirable for the transformation into phenolic compounds. The OMSs are valuable glycosidic compounds mainly synthesized by trans-glycosylation, which can find potential applications in cosmetics, foods, and healthcare. Therefore, a state-of-the-art OP holds a big promise of lowering the process cost by the valorization of these active compounds. Recent advances in organosolv modified components are reviewed, and perspectives are made for addressing future challenges.

An insight into the principles of lignocellulosic biomass-based zero-waste biorefineries: a green leap towards imperishable energy-based future

Lignocellulosic biomass (LCB) is an energy source that has a huge impact in today's world. The depletion of fossil fuels, increased pollution, climatic changes, etc. have led the public and private sectors to move towards sustainability i.e. using LCB for the production of biofuels and value-added compounds. A major bottleneck of the process is the recalcitrant nature of LCB. This can be overcome by using various pretreatment strategies like physical, chemical, biological, physicochemical, etc. Further, the pretreated biomass is made to undergo various steps like hydrolysis, saccharification, etc. for the conversion of value-added products and the remaining waste residues can be further utilized for the synthesis of secondary products thus favouring the zero-waste biorefinery concept. Currently, microorganisms are being explored for their use in biorefinery but the unavailability of commercial strains is a major limitation. Thus, the use of metagenomics can be used to overcome the limitation which is both cost-effective and environmentally friendly. The review deliberates the composition of LCBs, and their recalcitrance nature, followed by the structural changes caused by various pretreatment methods. The further steps in biorefineries, strategies for the development of zero-waste refineries, bottlenecks, and suggestions are also discussed. Special emphasis is given to the use of metagenomics for the discovery of microorganisms efficient for zero-waste biorefineries.

Simulation and optimization of organosolv based lignocellulosic biomass refinery: A review

Organosolv pretreatment can be considered as the core of the lignocellulosic biomass fractionation within the biorefinery concept. Organosolv facilitates the separation of the major fractions (cellulose, hemicelluloses, lignin), and their use as renewable feedstocks to produce bioenergy, biofuels, and added-value biomass derived chemicals. The efficient separation of these fractions affects the economic feasibility of the biorefinery complex. This review focuses on the simulation of the organosolv pretreatment and the optimization of (i) feedstock delignification, (ii) sugars production (mainly from hemicelluloses), (iii) enzymatic digestibility of the cellulose fraction and (iv) quality of lignin. Simulation is used for the technoeconomic optimization of the biorefinery complex. Simulation and optimization implement a holistic approach considering the efficient technological, economic, and environmental performance of the biorefinery operational units. Consequently, an optimized organosolv stage is the first step for a sustainable, economically viable biorefinery complex in the concept of industrial ecology and zero waste circular economy.

Recent advances in understanding the effects of lignin structural characteristics on enzymatic hydrolysis

Enzymatic hydrolysis of lignocellulose for bioethanol production shows a great potential to remit the rapid consumption of fossil fuels, given the fact that lignocellulose feedstocks are abundant, cost-efficient, and renewable. Lignin results in low enzymatic saccharification by forming the steric hindrance, non-productive adsorption of cellulase onto lignin, and deactivating the cellulase. In general, the non-productive binding of cellulase on lignin is widely known as the major cause for inhibiting the enzymatic hydrolysis. Pretreatment is an effective way to remove lignin and improve the enzymatic digestibility of lignocellulose. Along with removing lignin, the pretreatment can modify the lignin structure, which significantly affects the non-productive adsorption of cellulase onto lignin. To relieve the inhibitory effect of lignin on enzymatic hydrolysis, enormous efforts have been made to elucidate the correlation of lignin structure with lignin-enzyme interactions but with different views. In addition, contrary to the traditional belief that lignin inhibits enzymatic hydrolysis, in recent years, the addition of water-soluble lignin such as lignosulfonate or low molecular-weight lignin exerts a positive effect on enzymatic hydrolysis, which gives a new insight into the lignin-enzyme interactions. For throwing light on their structure-interaction relationship during enzymatic hydrolysis, the effect of residual lignin in substrate and introduced lignin in hydrolysate on enzymatic hydrolysis are critically reviewed, aiming at realizing the targeted regulation of lignin structure for improving the saccharification of lignocellulose. The review is also focused on exploring the lignin-enzyme interactions to mitigate the negative impact of lignin and reducing the cost of enzymatic hydrolysis of lignocellulose.

Discrepancy of lignin dissolution from eucalyptus during formic acid fractionation

Understanding the structure and properties of lignin has important practical significance for its further applications. In this case, eucalyptus was fractionated with 88% formic acid at 101 °C for different durations, and the removal efficiency as well as the chemical structure of lignin at various stages were comparatively analyzed. The obtained data indicated that with increasing reaction time, lignin was continuously removed and the process could be divided into three stages. The lignin dissolution rate was fast first and then slow, and the molecular weight of the dissolved lignin increased with time. The lignin structure was condensed and the molecular weight increased with prolonged of reaction time. Structural analysis indicated that the β-O-4' structure was largely destroyed, the G-type lignin dissolved early, and the degradation of the S-type lignin became more intensive with increasing reaction time. This is of great help for reaction control as well as the further processing of lignin byproducts.

Technologies for Eucalyptus wood processing in the scope of biorefineries: A comprehensive review

Eucalyptus is the most widely planted type of hardwoods, and represents an important biomass source for the production of fuels, chemicals, and materials. Its industrial benefit can be achieved by processes following the biorefinery concept, which is based on the selective separation ("fractionation") of the major components (hemicelluloses, cellulose and lignin), and on the generation of added-value from the resulting fractions. This article provides a in-depth assessment on the composition of Eucalyptus wood and a critical evaluation of selected technologies allowing its overall exploitation. These latter include treatments with organosolvents and with emerging fractionation agents (ionic liquids and deep eutectic solvents). The comparative evaluation of the diverse processing technologies is carried out in terms of degree of fractionation, yields and selectivities. The weak and strong points, challenges, and opportunities of the diverse fractionation methods are identified, focusing on the integral utilization of the feedstocks.

Biorefining Oat Husks into High-Quality Lignin and Enzymatically Digestible Cellulose with Acid-Catalyzed Ethanol Organosolv Pretreatment

Oat husks are low-value lignocellulosic residues of oat processing that carry an environmental impact. Their polymers (cellulose, hemicellulose, and lignin) can be converted into a wide variety of value-added products; however, efficient pretreatment methods are needed that allow their fine separation for further tailored valorization. This study pioneered the use of milling-free and low acid-catalyzed ethanol organosolv for the delignification of oat husks, allowing their conversion into three high-quality streams, namely, glucan-rich, lignin-rich, and hemicellulosic compound-rich streams. Temperature, retention time, and solid-to-liquid ratio were found to impact the delignification of oat husks when using a one-factor-at-a-time strategy. The ideal conditions that were found (210 °C, 90 min, and solid-to-liquid ratio of 1:2) culminated into glucan and lignin fractions containing 74.5% ± 11.4% glucan and 74.9% ± 7.6% lignin, respectively. These high-purity lignin fractions open the possibility for higher value applications by lignin, potentially impacting the feasibility of second generation biorefineries. The glucan fraction showed 90% digestibility after 48 h of hydrolysis with 10 filter paper units of enzyme cocktail per gram of glucan. Considering the absence of size reduction and high solid loading, together with the quality of the obtained streams, organosolv pretreatment could be a potential strategy for the valorization of oat lignocellulosic residues.

Improving the economy of lignocellulose-based biorefineries with organosolv pretreatment

Lignocellulose-based processes for production of value-added products still face bottlenecks to attain feasibility. The key might lie on the biorefining of all lignocellulose main polymers, that is, cellulose, hemicellulose and lignin. Lignin, considered an impediment in the access of cellulose and normally considered for energy recovery purposes, can give a higher contribution towards profitability of lignocellulosic biorefineries. Organosolv pretreatment allows selective fractionation of lignocellulose into separate cellulose-, hemicellulose- and lignin-rich streams. Ethanol organosolv and wood substrates dominated the research studies, while a wide range of substrates need definition on the most suitable organosolv pretreatment systems. Techno-economic and environmental analyses of organosolv-based processes as well as proper valorization strategies of the hemicellulose-rich fraction are still scarce. In view of dominance of ethanol organosolv with high delignification yields and high-purity of the recovered cellulose-rich fractions, close R & D collaboration with 1st generation ethanol plants might boost commercialization.

Preparation of porous biomass-derived hydrothermal carbon modified with terminal amino hyperbranched polymer for prominent Cr(VI) removal from water

Herein, a series of functionalized hydrochars with high density of nitrogen-containing functional groups were engineered by co-processing of terminal amino hyperbranched polymer and walnut shell biomass in the hydrothermal carbonization media. Hydrothermal Carbonization with optimized key parameters was implemented to determine the impact of added polymer to the biomass on the properties of the obtained hydrochars. Consequently, the optimum hydrochar which was achieved with the values of 250 °C, 60 min, and 50% (w/w) for temperature, time, and polymer/biomass weight ratio, demonstrated a highly improved surface area of 544 m².g^-1 and the highest adsorption capacity for Cr(VI) removal which was obtained from Freundlich isotherm model and described by the pseudo-second-order kinetic model to be 363.22 mg.g^-1 (at pH = 2.0). This work suggests that the co-hydrothermal carbonization promotes the uniform incorporation of polymers into the hydrochar matrix and provides adsorbents for the effective removal of Cr(VI) from water.