Processing Of Lignocellulosic Biomass Research Articles

Separate hydrolysis and fermentation of softwood bark pretreated with 2-naphthol by steam explosion

Background2-Naphthol, a carbocation scavenger, is known to mitigate lignin condensation during the acidic processing of lignocellulosic biomass, which may benefit downstream processing of the resulting materials. Consequently, various raw materials have demonstrated improved enzymatic saccharification yields for substrates pretreated through autohydrolysis and dilute acid hydrolysis in the presence of 2-naphthol. However, 2-naphthol is toxic to ethanol-producing organisms, which may hinder its potential application. Little is known about the implications of 2-naphthol in combination with the pretreatment of softwood bark during continuous steam explosion in an industrially scalable system.ResultsThe 2-naphthol-pretreated softwood bark was examined through spectroscopic techniques and subjected to separate hydrolysis and fermentation along with a reference excluding the scavenger and a detoxified sample washed with ethanol. The extractions of the pretreated materials with water resulted in a lower aromatic content in the extracts and stronger FTIR signals, possibly related to guaiacyl lignin, in the nonextractable residue when 2-naphthol was used during pretreatment. In addition, cyclohexane/acetone (9:1) extraction revealed the presence of pristine 2-naphthol in the extracts and increased aromatic content of the nonextractable residue detectable by NMR for the scavenger-pretreated materials. Whole-slurry enzymatic saccharification at 12% solids loading revealed that elevated saccharification recoveries after 48 h could not be achieved with the help of the scavenger. Glucose concentrations of 16.9 (reference) and 15.8 g/l (2-naphthol) could be obtained after 48 h of hydrolysis. However, increased inhibition during fermentation of the scavenger-pretreated hydrolysate, indicated by yeast cell growth, was slight and could be entirely overcome by the detoxification stage. The ethanol yields from fermentable sugars after 24 h were 0.45 (reference), 0.45 (2-naphthol), and 0.49 g/g (2-naphthol, detoxified).ConclusionThe carbocation scavenger 2-naphthol did not increase the saccharification yield of softwood bark pretreated in an industrially scalable system for continuous steam explosion. On the other hand, it was shown that the scavenger's inhibitory effects on fermenting microorganisms can be overcome by controlling the pretreatment conditions to avoid cross-inhibition or detoxifying the substrates through ethanol washing. This study underlines the need to jointly optimize all the main processing steps.

Mathematical modeling of the enzymatic hydrolysis of lignocellulosic waste in membrane bioreactor considering transport phenomena

Enzymatic hydrolysis is a crucial step in processing lignocellulosic biomass into biofuels and other valuable products in biorefineries. Applying a membrane reactor to realize this process allows for continuous separation of inhibitory end-products, thus improving process efficiency. Developed so far models have generally been dedicated to describing the reaction kinetics without considering transport phenomena and flux decline prediction. In the present paper, a new mathematical model simulating the hydrolysis process course in membrane bioreactor was established. Compared to previous reports, our study presents a novel approach to modeling the process accounting for the reaction course and permeate flux decline depending on reaction hydrodynamics. A surface renewal theory and empirical reaction kinetic model were implemented to simulate the influences of the operating parameters on the permeate flux and the monosaccharide concentration in the permeate. A procedure to determine the model parameters with experimental data was also presented. The proposed model simulated experimental data with good accuracy (R2>0.97). The total mass of glucose and xylose produced during 10 h of the hydrolysis performed under mixing conditions equaled 2.37 g and 2.39 g for the pressure of 0.4 and 0.6 bar, respectively. They correspond to the high hydrolysis yield, equaled in average to 99.1 %.

Upgrading lignocellulosic biomass to high-value products through the pretreatment driven by bio-based ethylene glycol solvent

Sustainable processing of lignocellulosic biomass is meaningful for comprehensive biomass conversion. Here, a ball milling (BM) assisted biomass-derived ethylene glycol (BEG) pretreatment is proposed to removes nearly 90 % of the lignin and increases cellulose accessibility by 3 times than raw biomass, facilitating subsequent enzymatic saccharification or catalytic conversion for 5-hydroxymethylfurfural (HMF), achieving yields of 92.9 % and 32.6 %. The synergistic effect of BM/BEG positively impacted delignification, followed by saccharification and HMF conversion. Introduction of biomass-derived solvent recovers the lignin with a well-preserved chemical structure, uniform molecular weight, short side chains, and high purity, making it highly suitable for downstream utilization. Density functional theory revealed hydrogen bonding and good miscibility between BEG and lignin units, suggesting reaction mechanisms and pathways. Molecular dynamics simulations showed that the solubilizing effect of BEG on lignin promoted cellulase-cellulose binding, thereby enhancing saccharification efficiency. The successful use of BEG solvents to maximize the biomass value is conducive to achieve closed-loop biorefinery approaches.

The response mechanism analysis of HMX1 knockout strain to levulinic acid in Saccharomyces cerevisiae.

Levulinic acid, a hydrolysis product of lignocellulose, can be metabolized into important compounds in the field of medicine and pesticides by engineered strains of Saccharomyces cerevisiae. Levulinic acid, as an intermediate product widely found in the conversion process of lignocellulosic biomass, has multiple applications. However, its toxicity to Saccharomyces cerevisiae reduces its conversion efficiency, so screening Saccharomyces cerevisiae genes that can tolerate levulinic acid becomes the key. By creating a whole-genome knockout library and bioinformatics analysis, this study used the phenotypic characteristics of cells as the basis for screening and found the HMX1 gene that is highly sensitive to levulinic acid in the oxidative stress pathway. After knocking out HMX1 and treating with levulinic acid, the omics data of the strain revealed that multiple affected pathways, especially the expression of 14 genes related to the cell wall and membrane system, were significantly downregulated. The levels of acetyl-CoA and riboflavin decreased by 1.02-fold and 1.44-fold, respectively, while the content of pantothenic acid increased. These findings indicate that the cell wall-membrane system, as well as the metabolism of acetyl-CoA and riboflavin, are important in improving the resistance of Saccharomyces cerevisiae to levulinic acid. They provide theoretical support for enhancing the tolerance of microorganisms to levulinic acid, which is significant for optimizing the conversion process of lignocellulosic biomass to levulinic acid.

Machine learning prediction of bio-polyol yields and hydroxyl values from acid-catalyzed liquefaction of lignocellulosic biomass

Amid the escalating demand for alternatives to petroleum resources and the imperative to decrease carbon emissions, there is an increasing interest in transforming lignocellulosic biomass into valuable chemicals. This study utilized machine learning models to analyze the acid-catalyzed liquefaction process of lignocellulosic biomass and to predict and characterize the yield and hydroxyl value (HV) of bio-polyols. A total of 612 yield data samples and 229 HV data samples were collected and analyzed. From these data, four machine learning models were constructed: Random Forest (RF), Gradient Boosting Regression (GBR), Gaussian Process Regression (GPR), and Support Vector Regression (SVR). The Bayesian Optimization Algorithm (BOA) was applied to refine the hyperparameters of the models, thereby enhancing their predictive accuracy. To clarify the effects of input features on predictive outcomes and to understand their interactive dynamics, one-dimensional and two-dimensional Accumulated Local Effects (ALE) analyses were performed. The results show that the GBR model was particularly precise in forecasting the yield and HV of bio-polyols, with corresponding test set determination coefficients (R2) of 0.82 and 0.91. The most influential factors on yield were reaction time (15.1 %), lignin content (13.1 %), and glycerol mass (12 %), while for HV, they were glycerol mass (28.9 %), particle size (15.1 %), and liquid-to-solid ratio (11.1 %). The ALE analysis also exposed the intricate interaction mechanisms between feedstock composition and liquefaction conditions. The verification results confirmed that the optimal model displayed exceptional generalization capabilities, with a Mean Absolute Percentage Error (MAPE) of 9.18 %. Utilizing this model, a user-friendly software package has been developed to enable rapid and precise prediction of the lignocellulosic biomass conversion process. This research not only delivers strategies to cut down on experimental costs and time but also offers a novel perspective on the industrial utilization of biomass-derived polyols.

Single-molecule tracking reveals dual front door/back door inhibition of Cel7A cellulase by its product cellobiose

Degrading cellulose is a key step in the processing of lignocellulosic biomass into bioethanol. Cellobiose, the disaccharide product of cellulose degradation, has been shown to inhibit cellulase activity, but the mechanisms underlying product inhibition are not clear. We combined single-molecule imaging and biochemical investigations with the goal of revealing the mechanism by which cellobiose inhibits the activity of Trichoderma reesei Cel7A, a well-characterized exo-cellulase. We find that cellobiose slows the processive velocity of Cel7A and shortens the distance moved per encounter; effects that can be explained by cellobiose binding to the product release site of the enzyme. Cellobiose also strongly inhibits the binding of Cel7A to immobilized cellulose, with a Ki of 2.1 mM. The isolated catalytic domain (CD) of Cel7A was also inhibited to a similar degree by cellobiose, and binding of an isolated carbohydrate-binding module to cellulose was not inhibited by cellobiose, suggesting that cellobiose acts on the CD alone. Finally, cellopentaose inhibited Cel7A binding at micromolar concentrations without affecting the enzyme's velocity of movement along cellulose. Together, these results suggest that cellobiose inhibits Cel7A activity both by binding to the "back door" product release site to slow activity and to the "front door" substrate-binding tunnel to inhibit interaction with cellulose. These findings point to strategies for engineering cellulases to reduce product inhibition and enhance cellulose degradation, supporting the growth of a sustainable bioeconomy.

Advanced pretreatment processes for lignocellulosic biomass to biofuels production: Path towards circular bioeconomy

Generation of biofuels obtained from lignocellulose biomass as a source can fundamentally decrease energy requirement from the conventional fossil fuels and their consecutive environmental effects. Circular bioeconomy concept has been established in the recent years for effective waste management which is the current need required to mitigate the deterioration of the environment. For that matter lignocellulosic biomass has been taken as a substrate for the fuel energy generation. In that regard, cellulosic ethanol as a substitute is likely to be able to grow as a feasible energy source in the upcoming future. For the last couple of decades, massive work has been performed to build cellulosic ethanol as an economical source with respect to the conventional nonrenewable source of fuel. The pretreatment step plays a significant role to break down the recalcitrant structures and to improve accessibility of cellulose to enzymes. An extensive amount of pretreatment techniques that involve physical, chemical, biological, and combined approaches have been adopted to test at the pilot scale. These techniques provide significant opportunities to lower the total cost, thus making large-scale production of cellulosic ethanol possible. This review discusses about the waste management with circular bioeconomy, various pretreatment techniques along with the mechanism of those pretreatments and some advanced pretreatment methods, their advantages followed by their parametric studies. Also, there is a discussion on lignocellulosic biomass acting as an aide in circular bioeconomy.

Imidazole as a new strategy in the lignocellulosic pretreatment: An application in corn sub-products with a focus on bioenergy production

To enhance the efficiency of pretreatment processes for lignocellulosic biomass, this study utilized the green solvent imidazole to pretreat residual corn biomass (corn straw (CS) and corncob (CC)) with a focus on cellulose recovery for ethanol production. The pretreatment involved varying temperatures (ranging from 120 to 180 °C) and times (30 and 60 min) with biomass:imidazole ratio of 1:9 (w.w−1). The effects of imidazole pretreatment on the biomasses were examined by analyzing the chemical composition, surface morphology, cellulose crystallinity, and compositional changes. The results demonstrated a significant alteration of the lignocellulosic complex due to imidazole pretreatment, resulting in a reduction of the lignin content, reaching 81.47 % and 74 % for CS (180°C-60min) and CC (180°C-30min), respectively. Moreover, the cellulose content in the pretreated solids increased by approximately 1.5 times compared to the raw biomass. The pretreated biomasses were subjected to enzyme hydrolysis (after pretreated at a higher temperature (150–180 °C)), which led to a high glucose yield. CC achieved a glucose yield of 100 %, while CS yielded 77 %. Alcoholic fermentation was carried out using Saccharomyces cerevisiae CAT-1, resulting in an ethanol yield of 82 % in 12 h for CC (180 °C for 30 min) and 66 % for CS (150 °C for 1 h).

Delignification of Different Lignocellulosic Biomass Using Hydrogen Peroxide and Acetic Acid (HPAC)

Lignocellulosic biomass will soon become the key source of feedstock for bioenergy to combat the impact of global warming and the depletion of fossil fuel resources. Lignin separation costs have been a key obstacle to bioenergy generation from lignocellulosic biomass. Pulp and paper, biofuel, and biomaterials sectors depend on wood delignification. This study examines delignification trends and advances, including standard and new methods. The study begins by explaining how delignification improves wood processability and value. It describes lignin's chemical structure and properties, highlighting its role in wood's mechanical and chemical qualities. Lignin from diverse lignocellulosic biomass sources is delignified using hydrogen peroxide and acetic acid in this study. A 1:1 hydrogen peroxide-acetic acid volume ratio was used after particle reduction. Experimental results show 96%, 89%, and 80% lignin removal efficiency for Ako, Mahogany, and mixed sawdust, respectively. A 30-minute reaction at 80°C yielded these results. The hydrogen peroxide-acetic acid mixture dignifies well and may be used in lignocellulosic biomass processing. This study also provides insights into optimizing delignification procedures and suggests approaches to improve the industrial use of lignocellulosic biomass. This study reveals that HPAC dignifies wood well. Understanding HPAC's role in the delignification of wood products could lead to developing an HPAC-based pretreatment technique that lowers the cost of biofuel generation from lignocellulosic biomass.

Molecular mechanism of cellulose depolymerization by the two-domain BlCel9A enzyme from the glycoside hydrolase family 9

Carbohydrate-active enzymes from the glycoside hydrolase family 9 (GH9) play a key role in processing lignocellulosic biomass. Although the structural features of some GH9 enzymes are known, the molecular mechanisms that drive their interactions with cellulosic substrates remain unclear. To investigate the molecular mechanisms that the two-domain Bacillus licheniformis BlCel9A enzyme utilizes to depolymerize cellulosic substrates, we used a combination of biochemical assays, X-ray crystallography, small-angle X-ray scattering, and molecular dynamics simulations. The results reveal that BlCel9A breaks down cellulosic substrates, releasing cellobiose and glucose as the major products, but is highly inefficient in cleaving oligosaccharides shorter than cellotetraose. In addition, fungal lytic polysaccharide oxygenase (LPMO) TtLPMO9H enhances depolymerization of crystalline cellulose by BlCel9A, while exhibiting minimal impact on amorphous cellulose. The crystal structures of BlCel9A in both apo form and bound to cellotriose and cellohexaose were elucidated, unveiling the interactions of BlCel9A with the ligands and their contribution to substrate binding and products release. MD simulation analysis reveals that BlCel9A exhibits higher interdomain flexibility under acidic conditions, and SAXS experiments indicate that the enzyme flexibility is induced by pH and/or temperature. Our findings provide new insights into BlCel9A substrate specificity and binding, and synergy with the LPMOs.

Delignifikacija kukuruznog oklaska pomoću peroksidnog predtretmana potpomognutog mikrotalasima

Lignocellulosic biomass comprises the crop residues, which remain in large quantities from various stages of crop processing. Its main constituents, cellulose, hemicellulose, and lignin, are interlinked by hydrogen and covalent bonds and form a robust and intricate matrix making it resistant to enzymatic degradation. Pretreatment is crucial in lignocellulosic biomass processing, aiming to remove lignin and enhance enzyme access to polysaccharides. This study examines how microwave-assisted peroxide pretreatment affects the delignification of corncobs, aiming to enhance the efficiency of utilizing this agricultural residue in fermentation processes. Taguchi orthogonal array was used to optimize pretreatment conditions and assess the effects of individual parameters (temperature, H 2 O 2 dose, and pretreatment time) on delignification efficiency. The results showed the significant influence of pretreatment conditions on lignin removal from corncobs, with the highest delignification achieved at an H 2 O 2 dose of 500 mg/g, temperature of 100 °C, and pretreatment time of 2 minutes. H 2 O 2 dose had the most substantial impact on the delignification, followed by temperature and pretreatment time. The observed 81.6% delignification and 61.9% increase in cellulose content are pivotal for enzymatic hydrolysis efficiency. This improvement suggests enhanced enzyme availability during hydrolysis and reversible binding to polysaccharide active sites, potentially leading to higher sugar yields.

Sustainable strategies to achieve industrial ethanol titers from different bioenergy feedstocks: scale-up approach for better ethanol yield

Hydrothermal pretreatment is a promising approach to lignocellulosic biomass processing for enzymatic hydrolysis and high-yield bioethanol fermentation, as it reduces downstream inhibitor content and the amount of toxic byproducts generated.

Optimizing Raw Material Pre-Treatment for Bioethanol Production from Empty Fruit Bunches: A Comparative Study

Bioethanol (C2H5OH) is an organic chemical widely used as a solvent. It is also applied in producing germicides, beverages, antifreeze, fuel, and depressants as an intermediate in producing other chemical substances. Generally, bioethanol is generated from the fermentation of glucose (sugar) accompanied by a distillation process. This study aimed to optimize bioethanol production against variations in pre-treatment and solvent concentrations through enzyme hydrolysis and fermentation of oil palm empty fruit bunches. The pre-treatment is an important stage in the conversion process of lignocellulosic biomass, as it eliminates lignin, reduces the crystallinity of the cellulose, and increases the porosity of the substance, thereby facilitating the hydrolysis process and glucose fermentation. The process was carried out with different concentrations of acid, base, and organolsov solvents, after that, it was hydrolyzed using cellulase enzymes for 24 hours and fermented using Saccharomyces Cerevisiae yeast for 5 days. Furthermore, the bioethanol produced was separated through a rotary vacuum evaporator at 180 rpm and a temperature of 78 °C. The highest ethanol content produced was 7.8% with 4% NaOH and 90 minutes of pre-treatment residence time.

Effect of biodrying of lignocellulosic biomass on humification and microbial diversity

By optimizing the carbon to nitrogen (C/N) ratio, this study accomplished an improved level of humification and microbial diversity in the biodrying process of lignocellulosic biomass. The results demonstrated that C/N ratio of 20 accelerated the decomposition of refractory lignocellulose, resulting in lower greenhouse gas emissions and the production of highly mature fertilizer with a germination index of 119.0% and a humic index of 3.2. Moreover, C/N ratio of 20 was found to diversify microbial communities, including Pseudogracilibacillus, Sinibacillus, and Georgenia, which contributed to the decomposition of lignocellulosic biomass and the production of humic acid. Hence, it is recommended to regulate the C/N ratio to 20:1 during the biodrying of biogas residue and wood chips to promote the economic feasibility and bioresource recycling.

Degradation of lignin in different lignocellulosic biomass by steam explosion combined with microbial consortium treatment

The difficulty of degrading lignin is the main factor limiting the high-value conversion process of lignocellulosic biomass. The biodegradation of lignin has attracted much attention because of its strong environmental friendliness, but it still faces some dilemmas such as slow degradation rate and poor adaptability. The microbial consortia with high lignin degradation efficiency and strong environmental adaptability were obtained in our previous research. To further increase the lignin degradation efficiency, this paper proposes a composite treatment technology of steam explosion combined with microbial consortium degradation to treat three kinds of biomass. We measured the lignin degradation efficiency, selectivity value (SV) and enzymatic saccharification efficiency. The structural changes of the biomass materials and microbial consortium structure were also investigated. The experimental results showed that after 1.6 MPa steam explosion treatment, the lignin degradation efficiency of the eucalyptus root reached 35.35% on the 7th days by microbial consortium. At the same time, the lignin degradation efficiency of the bagasse and corn straw treated by steam explosion followed by microbial biotreatment was 37.61–44.24%, respectively, after only 7 days of biotreatment. The microbial consortium also showed strong selectivity degradation to lignin. The composite treatment technology can significantly improve the enzymatic saccharification efficiency. Saccharomycetales, Ralstonia and Pseudomonadaceae were the dominant microorganisms in the biomass degradation systems. It was proved that the combined treatment technology of steam explosion and microbial consortium degradation could overcome the drawbacks of traditional microbial pretreatment technology, and can facilitate the subsequent high-value conversion of lignocellulose.

Study on the reaction mechanism of C8+ aliphatic hydrocarbons obtained directly from biomass by hydropyrolysis vapor upgrading

Aviation fuel production is an important direction for biomass utilization, however, the direct transformation of biomass into aviation fuel is a bottleneck in this field. Among all the biomass-to-liquid thermochemical routes, the pyrolysis process can directly produce bio-oil in a continuous industrial manner. Herein, Ni-Mo/γ-Al2O3 catalyst was used to investigate the hydropyrolysis (HP) vapor upgrading (VU) process of lignocellulosic biomass to obtain bio-oil with high selectivity of aviation fuel components. The VU temperature of 300–350℃ was conducive to generating liquid fuel with C8+ aliphatics as the main component of jet fuel. It was indicated that the yield of the oil phase was 6.4 wt% with an HHV of 46.2 MJ/kg, while the selectivity of aliphatics reached 72.6% with C8+ aliphatics was 59.9%. Moreover, it was found that all three components of biomass could be transformed into long-chain aliphatics by coupling reaction. The hydroxyalkylation is the main way and the aldehyde group is the directing group of the carbon-increasing, which was supported by the results of the quantum chemical calculation. Further, the reaction network for the HP-VU process of lignocellulosic biomass with C8+ aliphatics as the main product was proposed to provide a theoretical understanding of the carbon-increasing in biomass hydropyrolysis.

Bioenergy generation from thermochemical conversion of lignocellulosic biomass-based integrated renewable energy systems

Anthropogenic activities and advancements in industries boost global energy demand and increase fossil fuel consumption, causing several global environmental problems, such as climate change. As a climate change mitigation strategy, the use of renewable energy technologies has gained unprecedented interest. In particular, the thermochemical processing of lignocellulosic biomass integrated with other renewable energy technologies has emerged rapidly. It is critical to select appropriate integrated renewable energy system configurations for sustainable and feasible power generation towards higher environmental benefits. Understanding the possible configurations of thermochemical lignocellulosic biomass processing technologies (gasification, pyrolysis, hydrothermal gasification, or hydrothermal carbonization) integrated with renewable energy technologies (solar thermal, fuel cell, fusion power, or energy storage) is crucial for the further development and propagation of the integrated renewable energy system. Hence, we provide a systematic review of the thermochemical conversion of lignocellulosic biomass integrated with the other renewable energy technologies. Finally, the challenges associated with the implementation of these systems and suggestions for future research on the systems are discussed.

Spotlighting of the role of catalysis for biomass conversion to green fuels towards a sustainable environment: Latest innovation avenues, insights, challenges, and future perspectives

Recently, extensive resources were dedicated to studying how to use catalysis to convert biomass into environmentally friendly fuels. Problems with this technology include the processing of lignocellulosic sources and the development/optimization of novel porous materials as efficient monofunctional and bifunctional catalysts for biomass fuel production. This paper reviews recent advancements in catalysts procedures. Besides, it offers assessments of the methods used in catalytic biomass pyrolysis. Understanding the catalytic conversion process of lignocellulosic biomass into bio-oil remains a key research challenge in biomass catalytic pyrolysis.

Pharmaceutical applications of lignin-derived chemicals and lignin-based materials: linking lignin source and processing with clinical indication

Abstract Lignocellulosic biomass is one of the most abundant bioresources on Earth. Over recent decades, various valorisation techniques have been developed to produce value-added products from the cellulosic and hemicellulosic fractions of this biomass. Lignin is the third major component accounting for 10–30% (w/w). However, it currently remains a largely unused fraction due to its recalcitrance and complex structure. The increase in the global demand for lignocellulosic biomass, for energy and chemical production, is increasing the amount of waste lignin available. Approaches to date for valorizing this renewable but heterogeneous chemical resource have mainly focused on production of materials and fine chemicals. Greater value could be gained by developing higher value pharmaceutical applications which would help to improve integrated biorefinery economics. In this review, different lignin extraction methods, such as organosolv and ionic liquid, and the properties and potential of the extracted chemical building blocks are first summarized with respect to pharmaceutical use. The review then discusses the many recent advances made regarding the medical or therapeutic potential of lignin-derived materials such as antimicrobial, antiviral, and antitumor compounds and in controlled drug delivery. The aim is to draw out the link between the source and the processing of the biomass and potential clinical applications. We then highlight four key areas for future research if therapeutic applications of lignin-derived products are to become commercially viable. These relate to the availability and processing of lignocellulosic biomass, technologies for the purification of specific compounds, enhancements in process yield, and progression to human clinical trials.

History repeats itself again: Will the mistakes of the past for ILs be repeated for DESs? From being considered ionic liquids to becoming their alternative: the unbalanced turn of deep eutectic solvents

Comparing properties of ionic liquids, (deep) eutectic solvents and traditional organic solvents, as well as their applicability in lignocellulosic biomass processing.