Pretreatment Of Lignocellulosic Biomass Research Articles

A Review on Chemical Pretreatment of Lignocellulosic Biomass for the Production of Bioproducts: Mechanisms, Challenges and Applications

Excessive dependence on fossil resources to supply the increased energy demands has led to unsustainable growth. Hence, there is a necessity to shift our reliance from non-renewable to renewable resources. In this scenario, lignocellulosic biorefinery gains its importance because lignocellulosic biomass can be converted into various value-added products. However, biomass pretreatment is necessary due to the recalcitrant nature of the biomass. Various pretreatment techniques are employed to convert biomass into a more amenable structure to be utilized in the further steps of biorefinery. Hence, this review concentrates on different chemical pretreatment techniques used currently on biomass along with their modes of action on the biomass. This review will provide a detailed concept of various chemical pretreatments and the recent developments in pretreatment techniques. Despite this, the limitations of the current pretreatment strategies and the difficulties in their industrial applications are also discussed, which could provide innovative ideas to overcome these issues.

A Critical Review on Water Overconsumption in Lignocellulosic Biomass Pretreatment for Ethanol Production through Enzymic Hydrolysis and Fermentation

Global demand for renewable and sustainable energy fostered the considerable development of biomass-to-ethanol valorization strategies. Thermochemical pretreatment methods have been proposed to render biomass more amenable to enzymatic and microbial digestion. However, the efforts have not led to its industrial-scale worldwide realization. One of the obstacles to commercialization could be related to water overconsumption, as excessive water washing of the pretreated slurry is often performed to remove inhibitory compounds and residual chemicals after biomass pretreatment. Only increasing solid loading for biomass pretreatment results in ineffective pretreatment performance, more inhibitors formation, and high viscosity, which in turn necessitates the water washing step. A number of physicochemical and biological methods are applied to detoxify the acid-pretreated liquid fraction for enzymatic hydrolysis and fermentation. Among them, alkaline neutralization and liquid–liquid extraction are preferred because of their simple operation and low cost. Seemingly, recycling black liquor for alkali pretreatment offers a pathway to reduce water and chemical consumption, but alkali replenishment and inhibitor accumulation significantly weaken this technology. Interestingly, quite a few studies have removed the water washing and even solid–liquid separation steps after (liquid hot water, Tween 40, and CaO) pretreatment. There is still much room for future studies to render biomass pretreatment more feasible in terms of economic and environmental points of view. This review provides a deep understanding of wastewater generation during biomass upgrading and discusses the solutions to reduce water consumption critically.

Evaluation of the dissolving selectivity of ionic liquids for the three main components of bamboo powder under microwave irradiation

Understanding the dissolving selectivity of ionic liquids (ILs) for cellulose, hemicellulose, and lignin in plant cell wall is critical to explore new ILs for efficient pretreatment of lignocellulosic biomass. Here, the bamboo powder was treated at 150 ℃ under microwave irradiation by 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-butyl-3-methylimidazolium acetate (BmimAc) which had the different anions. The recovered bamboo powder and lignin samples were characterized. It indicated that the solubilities of bamboo powder in BmimCl and BmimAc were 27.04 and 7.00 g/100 g IL, respectively. A large amount of polysaccharides, especially hemicellulose, were possibly degraded by BmimCl, resulting in a low recovery rate (24.17 %) of bamboo powder with high content of lignin (41.81 %). The dissolving selectivity of BmimCl for the three main components was in the order: hemicellulose>cellulose>lignin, while that of BmimAc was in a different order: lignin>cellulose>hemicellulose. The dissolving selectivity of BmimAc was less obvious than that of BmimCl. The pretreatment of bamboo powder with BmimCl and BmimAc could greatly improve the yield of reducing sugar. BmimAc performed stronger ability than BmimCl to destroy the crystal structure of cellulose. Both the bamboo lignins extracted by BmimCl and BmimAc were syringyl (S)/guaiacyl (G)/p-hydroxyphenyl (H) type with different S/G/H ratios of 10.11/5.32/1.00 and 7.61/2.47/1.00, respectively. The lignin extracted by BmimAc was rich in hemicellulose and side alkyl chains. While the β-O-4 bonds in the lignin extracted by BmimCl were seriously broken, leading to the high contents of aliphatic OH, syringyl phenolic OH, and guaiacyl phenolic OH. BmimAc performed weaker ability than BmimCl to damage the lignin structure.

Revealing adsorption of mixed enzymes onto lignin resulted from integration of hydrothermal and chemi-mechanical pretreatment

Lignin is the main factor inhibiting enzymatic hydrolysis of lignocellulosic biomass. Different pretreatments can alter chemical and structural characteristics of lignin, thus affecting its adsorption capacity of enzymes. Herein, enzymatic mild acid lignin (EMAL) was separated from poplar branch wood chips as substrates resulted from different combined pretreatments, and then characterized and adsorbed by enzymes, so as to study the effects of different pretreatments on enzyme adsorption capacity. The results showed that the phenolic hydroxyl content and CC bond number of lignin increased after hydrothermal pretreatment, which increased the unproductive adsorption of mixed enzymes through hydrophobic interaction and hydrogen bonds. Chemical pretreatment after hydrothermal pretreatment can further reduce the unproductive adsorption of lignin on mixed enzymes, improving the enzymatic hydrolysis of substrates. This study would help to unmask the adsorption of mixed enzymes on lignin resulted from combined pretreatments, and facilitate the rapid development of efficient pretreatment for lignocellulosic biomass.

The potential of imidazole as a new solvent in the pretreatment of agro-industrial lignocellulosic biomass

Lignocellulosic biomass is a renewable material of great abundance. However, its recalcitrant characteristic requires the application of pretreatments. Sugarcane bagasse (SB), soybean hulls (SH), cocoa pod husks (CPH) and oil palm empty fruit bunches (OPEFB) were subjected to imidazole pretreatment in order to evaluate chemical composition variations and influence over enzymatic hydrolysis efficiency. Non-treated SH, SB and OPEFB have higher content of holocellulose, while CPH is rich in lignin polymers (31.2%). After imidazole-pretreatment, all biomasses presented structural disorganization of lignocellulosic fibres and enrichment in the percentage of cellulose. Levels of up to 72% delignification were obtained, which allowed an enzymatic conversion greater than 95% for SB, SH and OPEFB, while only 83% was reached for CPH. Imidazole is then emerging as a potential catalyst for the pretreatment of agro-industrial by-products, allowing the valorisation of these residues and their reinsertion into the production chain under a biorefinery concept.

Effect of alkali salt-coupled ball milling pretreatment of wheat straw on improving enzymatic hydrolysis and energy efficiency

Pretreatment of lignocellulosic biomass is crucial in producing fermentable sugars in a sustainable biorefinery. In this study, wheat straw was pretreated with a combination of ball milling (BM) and NaAlO2 particles (NaAlO2-BM) for enzymatic hydrolysis within a short hydrolysis period. The effects of energy consumption on modifications of physicochemical proprieties and energy efficiency were elucidated. NaAlO2-BM pretreatment decreased particle size rapidly to tissue scale in 10 min with energy consumption reduced by 0.5 times compared to BM pretreatment. NaAlO2-BM pretreated for 20 min achieved a glucose yield of 95.4% at a cellulase loading of 10 FPU/g dry substrate for 24 h enzymatic hydrolysis and provided the highest energy efficiency of 0.121 kg glucose/kWh, increasing by 1.1 times than BM pretreatment. Energy consumption showed a positive relationship with cellulose content while it negatively correlated with median particle size, cellulose crystallinity and energy efficiency. The combination of BM and NaAlO2 particles was demonstrated to be a promising pretreatment approach for glucose production and improving energy efficiency during hydrolysis of lignocellulose.

Green production of prebiotic xylooligosaccharides via enzymatic hydrolysis from xylan black liquor of oil palm frond

The black liquor generated from the alkaline pretreatment of lignocellulosic biomass is usually disposed of into wastewater, which could lead to environmental pollution. Alkaline black liquor (ALBL) contains a large amount of xylan with a small fraction of lignin, making it a promising raw material for the production of xylooligosaccharides (XOS). In this study, xylan was extracted from the ALBL generated upon treating the oil palm frond (OPF) with sodium hydroxide via two-stage precipitation for the separation of lignin and recovery of xylan. As a result, approximately 84.0% of xylan retrieved from the ALBL was recovered. Subsequently, enzymatic hydrolysis was optimized to recover the maximum amount of XOS from xylan. The results showed that enzymatic hydrolysis produced the highest XOS (62.5%) under optimal conditions of 50 °C, 4 U/mL xylanase, and 3% xylan loading for 48 h. The study provides insight for maximizing utilization of ALBL of OPF for future biorefinery economy.

A temperature control system for batch pretreatments of lignocellulosic biomass: proposal, implementation and evaluation

A temperature control system for batch pretreatments of lignocellulosic biomass: proposal, implementation and evaluation

Intensification of enzymatic saccharification at high solid loading of pretreated agave bagasse at bioreactor scale

Enzymatic saccharification of pretreated lignocellulosic biomass is a key step in the biochemical biorefineries. To be economically practical for large-scale use, the process must be run at high solids loadings, notably biomass concentrations of more than 15 % (w/v). However, as the solids loading increases, biomass develops a high-viscosity slurry that is severely mass transfer constrained and more difficult to mix, which restricts the addition of even more solids. Using a commercial enzyme mixture of cellulases and hemicellulases, high solid loading hydrolysis of hydrothermally and CO2-H2O pretreated agave bagasse was carried out in a continuous stirred tank bioreactor (CSTBR) and horizontal bioreactor (HB) to generate high glucose concentrations. With complete saccharification of 100 %, operation at the CSTBR at 20 % (w/v) solid loading yielded 119.9 g/L of glucose concentration, while operating at the HB at the same level of substrate loading was able to produce 134.4 g/L of glucose concentration. CO2-H2O pretreated biomass produced 123.6 g/L of glucose at the same loading on operation with a HB. The hydrolysis was greatly enhanced by the enzyme mixture. The current glucose conversion outcomes of hydrothermally processed biomass were unquestionably greater, with an energy efficiency 2.291 gsugar/MJ. The results of the present study conclusively show the concentration of glucose working at high solid loading by analyzing the energy consumption to improve the mechanical phenomenon at the stage of pretreatment hydrolysis. For the development of biorefineries, the design and development of this process will enable the establishment of ideal operating conditions and energy efficiency.

Correction: Non-catalytic proteins as promising detoxifiers in lignocellulosic biomass pretreatment: unveiling the mechanism for enhanced enzymatic hydrolysis

Correction for ‘Non-catalytic proteins as promising detoxifiers in lignocellulosic biomass pretreatment: unveiling the mechanism for enhanced enzymatic hydrolysis’ by Meysam Madadi et al., Green Chem., 2023, https://doi.org/10.1039/d3gc01718d.

Non-catalytic proteins as promising detoxifiers in lignocellulosic biomass pretreatment: Unveiling the mechanism for enhanced enzymatic hydrolysis

Dilute acid (DA) pretreatment of biomass generates multiple inhibitory compounds within the pretreatment hydrolysates. These compounds subsequently contribute to the formation of pseudo-lignin on the surfaces of the substrate, consequently...

Extraction and characterization of lignocellulosic agricultural biomass pretreatment method for biofuel

Extraction and characterization of lignocellulosic agricultural biomass pretreatment method for biofuel

Deep Eutectic Solvents for Biotechnology Applications

Deep eutectic solvents (DESs) are an alternative to traditional organic solvents and ionic liquids and meet the requirements of "green" chemistry. They are easy to prepare using low-cost constituents, are non-toxic and biodegradable. The review analyzes literature on the use of DES in various fields of biotechnology, provides data on the types of DESs, methods for their preparation, and properties. The main areas of using DESs in biotechnology include extraction of physiologically active substances from natural resources, pretreatment of lignocellulosic biomass to improve enzymatic hydrolysis of cellulose, production of bioplastics, as well as a reaction medium for biocatalytic reactions. The aim of this review is to summarize available information on the use of new solvents for biotechnological purposes.

Construction of anhydrous two-step organosolv pretreatment of lignocellulosic biomass for efficient lignin membrane-extraction and solvent recovery

Glycerol organosolv (GO) pretreatment has been revealed to be potent in selectively deconstructing the lignocellulosic biomass and effectively enhancing its enzymatic hydrolysis, but the conventional solid washing and GO lignin extraction processes frequently consume large amounts of water, resulting additionally in difficulty recycling the glycerol. In this study, an anhydrous two-step organosolv pretreatment process was explored, followed by the membrane ultrafiltration of glycerol lignin. The results showed that the solid washing of the residual glycerol after the atmospheric glycerol organosolv (AGO) pretreatment was necessary for the subsequent operation of high-solid enzymatic hydrolysis. Washing with ethanol was desirable as an alternative to water as only a low glycerol content of 5.2% resided in the substrate. Membrane ultrafiltration was helpful in extracting the AGO lignin from the pretreatment liquor, in which a high lignin extraction of 81.5% was made with a regenerated cellulose membrane (cut-off for 1 kDa) under selected ultrafiltration conditions. With the characterization of membrane-extracted lignin, it was observed for the first time that the AGO lignin has a well-preserved structure of G/S type. Moreover, the lignin was enriched with reactive groups, i.e. β-O-4′ linkages and aliphatic hydroxyl groups, which was very likely due to the glycerol grafting onto the lignin via α-etherification reaction. The two-step organosolv pretreatment process allowed 86% of glycerol and 92% of the ethanol recovery with ∼78% of distillation energy savings, which was applicable for extraction of organosolv lignin and recycling use of organic solvents.

Conditioning of pretreated birch by liquid-liquid organic extractions to improve yeast fermentability and enzymatic digestibility.

By-products from hydrothermal pretreatment of lignocellulosic biomass inhibit enzymatic saccharification and microbial fermentation. Three long-chain organic extractants (Alamine 336, Aliquat 336 and Cyanex 921) were compared to two conventional organic solvents (ethyl acetate and xylene) with regard to conditioning of birch wood pretreatment liquid (BWPL) for improved fermentation and saccharification. In the fermentation experiments, extraction with Cyanex 921 resulted in the best ethanol yield, 0.34 ± 0.02 g g-1 on initial fermentable sugars. Extraction with xylene also resulted in a relatively high yield, 0.29 ± 0.02 g g-1, while cultures consisting of untreated BWPL and BWPL treated with the other extractants exhibited no ethanol formation. Aliquat 336 was most efficient with regard to removing by-products, but the residual Aliquat after the extraction was toxic to yeast cells. Enzymatic digestibility increased by 19-33% after extraction with the long-chain organic extractants. The investigation demonstrates that conditioning with long-chain organic extractants has the potential to relieve inhibition of both enzymes and microbes.

Microbial Lignocellulolytic Enzymes for the Effective Valorization of Lignocellulosic Biomass: A Review

The urgent demand for alternative energy sources has been sparked by the tremendous burden on fossil fuels and the resulting acute energy crisis and climate change issues. Lignocellulosic biomass is a copious renewable and alternative bioresource for the generation of energy fuels and biochemicals in biorefineries. Different pretreatment strategies have been established to overcome biomass recalcitrance and face technological challenges, such as high energy consumption and operational costs and environmental hazards, among many. Biological pretreatment using microbial enzymes is an environmentally benign and low-cost method that holds promising features in the effective pretreatment of lignocellulosic biomass. Due to their versatility and eco-friendliness, cellulases, hemicellulases, and ligninolytic enzymes have been recognized as “green biocatalysts” with a myriad of industrial applications. The current review provides a detailed description of different types of lignocellulolytic enzymes, their mode of action, and their prospective applications in the valorization of lignocellulosic biomass. Solid state fermentation holds great promise in the microbial production of lignocellulolytic enzymes owing to its energy efficient, environment friendly, and higher product yielding features utilizing the lignocellulosic feedstocks. The recent trends in the application of enzyme immobilization strategies for improved enzymatic catalysis have been discussed. The major bottlenecks in the bioprocessing of lignocellulosic biomass using microbial enzymes and future prospects have also been summarized.

Solubility Study of Lignin Monomeric Compounds in Deep Eutectic Solvents for Biomass Waste Pre-treatment

Lignin is a complex polymer class formed from the cell wall, it is an organic polymer with a variety of biological aspects and industrial applications. Deep eutectic solvent (DES) has been introduced as a green solvent to dissolve lignin from lignocellulosic biomass. DESs typically have low vapor pressure, high heat stability, low toxicity and biodegradation which are the ideal features for lignocellulosic biomass pre-treatment. In this work, Conductor-like Screening Model for Real Solvents (COSMO-RS) was used to determine the suitable DESs for lignin degradation. The performance of the selected DESs was tested on lignin monomeric compounds, commercial lignin and the actual biomass of oil palm empty fruit bunch (OPEFB). Three DESs were used to test its lignin dissolution capability, i.e. choline chloride:urea (ChCl:Ur) (1:2), choline chloride:glycerol (ChCl:Gly) (1:2) and choline chloride:glucose ( ChCl:Glu) (1:1). The saturation points of dissolving each lignin type were determined for each DES. It was experimentally found that ChCl:Ur (1:2) could dissolve more lignin than ChCl:Gly (1:2) and ChCl:Glu (1:1). This work shows the possibility of using DES to dissolve lignin structures for biomass pretreatment and utilization.

A Chemical-Free Pretreatment for Biosynthesis of Bioethanol and Lipids from Lignocellulosic Biomass: An Industrially Relevant 2G Biorefinery Approach

A wide range of inorganic and organic chemicals are used during the pretreatment and enzymatic hydrolysis of lignocellulosic biomass to produce biofuels. Developing an industrially relevant 2G biorefinery process using such chemicals is challenging and requires more unit operations for downstream processing. A sustainable process has been developed to achieve industrially relevant titers of bioethanol with significant ethanol yield. The pretreatment of sorghum biomass was performed by a continuous pilot-scale hydrothermal reactor followed by disk milling. Enzymatic hydrolysis was performed without washing the pretreated biomass. Moreover, citrate buffer strength was reduced to 100-fold (50 mM to 0.5 mM) during the enzymatic hydrolysis. Enzymatic hydrolysis at 0.5 mM citrate buffer strength showed that significant sugar concentrations of 222 ± 2.3 to 241 ± 2.3 g/L (glucose + xylose) were attained at higher solids loadings of 50 to 60% (w/v). Furthermore, hydrolysates were fermented to produce bioethanol using two different xylose-fermenting Saccharomyces cerevisiae strains and a co-culture of xylose-fermenting and non-GMO yeast cultures. Bioethanol titer of 81.7 g/L was achieved with an ethanol yield of 0.48 gp/gs. Additionally, lipids were produced using the oleaginous yeast Rhodosporidium toruloides, yielding 13.2 g/L lipids with cellular lipid accumulation of 38.5% w/w from 100 g/L of sugar concentration. In summary, reducing the strength of the citrate buffer during enzymatic hydrolysis and omitting inorganic chemicals from the pretreatment process enhances the fermentability of hydrolysates and can also reduce operating costs.

Multivariate regression and artificial neural network modelling of sugar yields from acid pretreatment and enzymatic hydrolysis of lignocellulosic biomass

Reducing sugar generation from lignocellulosic biomass (LCB) is closely linked with biomass characteristics, pretreatment and enzymatic hydrolysis conditions. In this study curated experimental data from literature was used to develop multivariate regression and artificial neural network (ANN) model considering nine predictors (i.e., cellulose, hemicellulose, lignin content, cellulose-lignin ratio, acid concentration, temperature, time, pretreatment severity, and enzyme concentration). Selected reduced polynomial model (R2: 0.891, Adj. R2: 0.849) suggests positive influence of acid and enzyme, while negative influence of treatment severity, temperature and time on reducing sugar generation. Genetic algorithm-optimized ANN model offered excellent fitness for LCB hydrolysis on training (R2: 0.997), validation (R2: 0.984), and test sets (R2: 0.967). Sensitivity analysis of the ANN predictors suggests lignin and to some extent hemicellulose contents can be inhibitory. Though polynomial models can have simple interpretation, use of optimized ANN offers better predictability in dataset with diverse biomass compositions.

Pretreatment of Paddy Husk Used for Bioethanol Production with Deep Eutectic Solvent

Agricultural wastes as lignocellulosic biomass have shown good potential for producing bioethanol. There are three main steps in the production of bioethanol from lignocellulosic biomass; pretreatment, hydrolysis, and fermentation. Expanding the surface area of biomass, dissolving hemicellulose and/or lignin, and reducing the particle sizes of biomass are the most important goals of the pretreatment stage. Deep eutectic solvents (DES) are used widely in the pretreatment of lignocellulosic biomass. In this study, the deep eutectic solvent (DES) was used in the pretreatment of paddy husk. The effect of molar ratios of ChCl/Boric acid (1:1, 1:2, 2:1) on lignin removal percentage was investigated. As a result, the highest lignin removal percentage was obtained as 8.5% by using the molar ratio of 1:1. Obtained results were confirmed by ATR/FT-IR analyses.