Efficient Delignification Research Articles

Improved sugar recovery from enzymatic hydrolysis of Miscanthus sinensis by surfactant-mediated alkaline pretreatment

Surfactants play a vital role in the removal of lignin and subsequent enzymatic saccharification of lignocellulosic biomass. In this work, a surfactant-mediated alkaline pretreatment (SMAP) with short residence time and low NaOH loading has been successfully developed for enhancing enzymatic hydrolysis of a potential energy plant, Miscanthus sinensis, and evaluating its potential as a feedstock for biofuel production. As compared to individual alkaline pretreatment (AP), the SMAP process resulted in significantly more hemicellulose removal, more efficient delignification, higher cellulose content (55% vs. 51%), and stronger morphological disruption of the pretreated stalks, making them more accessible to cellulases and/or microorganisms. As a result, SMAP produced a significantly higher sugar yield of 402.5 mg/g than the control and AP group (287.8 mg/g) (p < 0.05). Among the tested surfactants, Tween 40 was identified as a potential candidate for SMAP of biomass wastes. SMAP with mild conditions (i.e., 121 °C, 10 min, 1.0% NaOH, 1.0% Tween 40) gave the highest sugar yield of 566.0 mg/g, which were 6.5-folds greater than the raw stalk. These demonstrations for using SMAP to achieve enhanced lignin removal and sugar recovery from biomass highlight its strong application potentials of improving bioconversion of lignocellulosic biomass like Miscanthus sinensis, hence making this crop a valuable energy plant.

An extensive parameter study of hydrotropic extraction of steam-pretreated birch

Efficient fractionation of lignocellulosic biomass is an important step toward the replacement of fossil-based products. However, the utilisation of all of the components in biomass requires various fractionation techniques. One promising process configuration is to apply steam explosion for the recovery of hemicelluloses and a subsequent hydrotropic extraction step for the delignification of the remaining solids. In this work, the influence of residence time, temperature and biomass loading on lignin recovery from birch using sodium xylene sulphonate as a hydrotrope was investigated. Our results show that residence time, temperature and biomass loading correlate positively with lignin extraction, but the effects of these parameters were limited. Furthermore, when steam explosion was implemented as the initial step, hydrotropic extraction could be performed even at room temperature, yielding a lignin extraction of 50%. Also, hydrothermal degradation of the material was necessary for efficient delignification with sodium xylene sulphonate, regardless of whether it occurs during steam explosion pretreatment or is achieved at high temperatures during the hydrotropic extraction.

Assessment of the papermaking potential of processed Miscanthus × giganteus stalks using alkaline pre-treatment and hydrodynamic cavitation for delignification

One way of satisfying increased market demand and simultaneously achieving a reduced environmental load in the industrial paper production is the use of fibrous agricultural residues. The aims of this study were i) to investigate the effect of alkaline – hydrodynamic cavitation (HC) pre-treatments on the delignification of Miscanthus × giganteus stalks (MGS) and ii) establishing the suitability of MGS as feedstock and their exploitation in pulp and paper manufacturing. It was demonstrated that the proposed treatment is an efficient delignification method for the non-wood fiber sources, such as miscanthus. A significant outcome of this work was the observation that HC treatment preserved the fibres lengths and surface quality of raw MGS, but at the same time increased the amount of kinked and curled fibers present in cavitated miscanthus fibers. The average miscanthus fiber length was found to be relatively short at 0.45 (±0.28) mm, while the slenderness ratio, the flexibility coefficient and Runkel ratio values were calculated to be 28.13, 38.16 and 1.62, respectively. The estimated physical properties of MGS pulp hand-sheets were 24.88 (±3.09) N m g−1 as the tensile index, 0.92 (±0.06) kPa m2 g−1 as the burst index and 4.0 (±0.37) mN m2 g−1 as the tear index. Overall the current work demonstrated effective use of hydrodynamic cavitation for improving the processing in pulp and paper manufacturing.

Investigation of pretreatment parameters in the delignification of paddy husks with deep eutectic solvents

In the present study, the delignification of paddy husks was carried out with ethylene glycol (EG)/citric acid (CA) deep eutectic systems (DES). The effects of the molar ratio of DES components, pretreatment temperature and pretreatment time on the lignin removal efficiency were investigated. The approximate quantitative analysis, ATR/FT-IR spectra and SEM-EDS analysis of untreated and pretreated samples were used to determine the lignin removal from paddy husks. The results obtained with ATR/FT-IR spectra and approximate analysis were determined to be consistent and supported the removal of lignin from the structure. The analysis results showed that the silica, which gives chemical strength to the structure, was also removed from the structure. Using DES systems with EG/CA molar ratios of 1:1, 1:2 and 2:1, lignin removal percentages at 90 °C were found to be 47.10%, 52.35% and 51.17%, respectively. The obtained results showed that two important parameters affecting the removal of lignin from the paddy husk are the pretreatment temperature and time. It was concluded that at high temperatures, intermolecular hydrogen bonds are weakened, the viscosity of the DES solution decreases, DES penetrates the lignocellulosic structure easily and thus the lignin removal efficiency is increased. The highest lignin removal percentage was found as 57.33% after 4 h of pretreatment time at 120 °C. The results showed that efficient delignification of paddy husks is possible using EG/CA DES systems.

Insights into delignification behavior using aqueous p-toluenesulfonic acid treatment: comparison with different biomass species

Exploring an efficient delignification technique is imperative for further advance on biorefinery, together with elucidation on affecting factors and mechanism of delignification. Biomass fractionation using the aqueous p-toluenesulfonic acid (p-TsOH) changed tremendously with biomass species. Herein, effect of biomass species on delignification using the aqueous p-TsOH treatment was investigated. Compared to cellulose and hemicelluloses removal, delignification was greatly affected by biomass species, and delignification of softwood was the toughest. The dissolved lignin and residual lignin in the pretreated biomass, together with the original lignin without pretreatment were determined, analyzed and compared using various techniques. Essentially, the active linkages and groups in the dissolved lignin decreased compared to the original lignin from TGA and GPC analysis. However, the primary structure of lignin was not drastically altered after treatment from FTIR results. The high content of phenolic hydroxyl and the hydrophilic carboxyl in the original lignin of hardwood and grass were detected, which mainly accounted for their super solubility during the aqueous p-TsOH treatment. Moreover, the active aryl ether linkages reduced and C–C linkages increased for softwood after treatment. Compared with the guaiacyl unit, dissolution of the syringyl and p-hydroxyphenyl units were readily achieved. Therefore, the ideal feedstocks for the aqueous p-TsOH treatment are hardwood and grass species.

Effect of p-TsOH pretreatment on separation of bagasse components and preparation of nanocellulose filaments.

The efficient separation of bagasse components was achieved by p-toluenesulfonic acid (p-TsOH) pretreatment. The effects of p-TsOH dosage, reaction temperature and reaction time on cellulose, hemicellulose and lignin contents were studied. Eighty-five per cent of lignin was dissolved, whereas the cellulose loss was minimal (less than 8.1%). Cellulose-rich water-insoluble residual solids were obtained. The degree of polymerization of cellulose decreased slightly, but the crystallinity index (CrI) increased from 52.0% to 68.1%. It indicated that the highly efficient delignification of bagasse was achieved by p-TsOH pretreatment. The nanocellulose filaments (CNFs) were produced by the treated samples. The physico-chemical properties of CNFs were characterized by transmission electron microscopy and thermogravimetric analysis. The results show that the CNFs have smaller average size and higher thermal stability. It provides a new method for CNFs.

Liquid ammonia pretreatment optimization for improved release of fermentable sugars from sugarcane bagasse

Alkali pretreatment of biomass is a widely accepted method for efficient delignification causing significant recovery of pentoses and hexoses to be utilized for second generation ethanol production. Present study is investigated to optimize the conditions of liquid ammonia pretreatment of sugarcane bagasse using statistical design of response surface methodology with respect to liquid ammonia concentration (15–25% v/v), solid loading (5–20% w/v), temperature (70–100 °C) and retention time (16–24 h) for maximum recovery of sugars during enzymatic hydrolysis. Optimized conditions for liquid ammonia pretreatment were found as 15.64% (v/v) ammonia; 10.51% (w/v) solid loading; 84.9 °C temperature; and 23.95 h retention time. The reducing sugar yield of 545.57 ± 7.1 g/kg of raw biomass corresponding to 75.41 ± 1% of maximum theoretical sugars was achieved after 72 h of saccharification using Cellic CTec 2 (20 FPU/g pretreated biomass). Biophysical techniques further validated the efficiency of process via deeper understanding of structural and compositional changes of pretreated as well as saccharified biomass imprinted by optimized pretreatment conditions used in the study.

Wheat straw components fractionation, with efficient delignification, by hydrothermal treatment followed by facilitated ethanol extraction

Lignocellulosic biomass fractionaion into its three major components is critically important for efficient feedstock utilization. The hydrothermal-ethanol method has broad application as its first step, hydrothermal treatment, provides high hemicellulose separation efficiency. However, it severely inhibits the delignification on the subsequent ethanol extraction. In this study, the second step, ethanol extraction, was facilitated by the addition of 3% NaOH and 3% H2O2, resulting in a significant improvement of lignin separation (by 48.2%). SEM, AFM, XPS, and XRD were used to characterize the surface composition of the remaining solids (crude cellulose) while the structure of isolated lignin was characterized by FT-IR, CP/MAS 13C NMR, GPC and TGA. The lignin samples isolated with both facilitated and non-facilitated ethanol extraction were compared to elucidate the lignin removal mechanism. The results showed that lignin degradation and crosslinking/polymerization occur in parallel during both the hydrothermal treatment and ethanol extraction.

Choline chloride-based deep eutectic solvents for efficient delignification of Bambusa bambos in bio-refinery applications

The use of choline chloride–oxalic acid (CO) and choline chloride–urea (CU) green solvents as mediator for delignification of Bambusa bambos stem (BS) has been studied. The optimal delignification of BS obtained at 120 °C and 4 h of DESs (deep eutectic solvents) treatment process. The morphological structure of raw BS and treated BS was analyzed by SEM, XRD, and FTIR. The results showed that the crystallinity index increased from 43.8 in raw BS, to 44.3%, and CUT-BS and 46.4 in COT-BS. The surface elemental composition of BS was estimated by photoelectron spectroscopy (XPS). The carbon and oxygen elemental contents in the biomass surface were determined by XPS survey, C1s, and O1s spectra. The delignification using CO system (25.4%) more easily digested the BS biomass compared to CU system (19.4%). The use of acid DES can be an effective pretreatment process compared to basic treatment processes for biomass fractionation in bio-refinery applications.

Quantitative structures and thermal properties of Miscanthus × giganteus lignin after alcoholamine-based ionic liquid pretreatment

Alcoholamine-based ionic liquid (IL) pretreatment has been potential due to low cost (∼$1.0/kg) and efficient delignification. However, valuable exploration of lignin during this pretreatment has not been systematically studied and this hinders its further commercialized application. In this study, the effects of mild and efficient ethanolamine acetate [EOA][OAc] pretreatment on the structural and thermal feature of Miscanthus × giganteus (M×g) lignin were evaluated in detail. The ionic liquid lignin (ILL), and residual-enzymatic hydrolysis-mild acidolysis lignin (R-EMAL) were compared with the original-enzymatic hydrolysis-mild acidolysis lignin (O-EMAL). Results determined that Guaiacyl (G) was the predominant unit in all the lignins. As compared to O-EMAL, ILL had higher yield, high purity, less β-O-4 ether linkages, and more COOH contents as well as a higher thermal stability owing to formation of slightly condensed structures. Additionally, depolymerization of the lignin occurred as the reduction of the molecular weight, and cleavage of β-O-4 ether linkages. Furthermore, R-EMAL was similar to O-EMAL as approximative β-O-4 ether linkages, molecular weight and thermal stability. The structural elucidation of M×g lignin could provide a good theoretical basis for economic improvement of the alcoholamine-based biorefinery and efficient conversion of lignocellulose to high value-added lignin-based products.

Complementing Vanillin and Cellulose Production by Oxidation of Lignocellulose with Stirring Control

Lignin transformation to high-value chemicals is key for forthcoming biorefineries. Here, we report efficient delignification of pine wood by oxidative biorefining in aqueous alkali, producing both...

Fractional Profiling of Kraft Lignin Structure: Unravelling Insights on Lignin Reaction Mechanisms

The kraft process is the main process used for the production of chemical pulps. In this process, an efficient delignification is achieved, yielding bleachable grade pulps. In recent years, there h...

Pretreatment of sweet sorghum straw and its enzymatic digestion: insight into the structural changes and visualization of hydrolysis process

BackgroundThe efficient utilization of lignocellulosic biomass for biofuel production has received increasing attention. Previous studies have investigated the pretreatment process of biomass, but the detailed enzymatic hydrolysis process of pretreated biomass remains largely unclear. Thus, this study investigated the pretreatment efficiency of dilute alkali, acid, hydrogen peroxide and its ultimate effects on enzymatic hydrolysis. Furthermore, to better understand the enzymatic digestion process of alkali-pretreated sweet sorghum straw (SSS), multimodal microscopy techniques were used to visualize the enzymatic hydrolysis process.ResultAfter pretreatment with alkali, an enzymatic hydrolysis efficiency of 86.44% was obtained, which increased by 99.54% compared to the untreated straw (43.23%). The FTIR, XRD and SEM characterization revealed a sequence of microstructural changes occurring in plant cell walls after pretreatment, including the destruction of lignin–polysaccharide interactions, the increase of porosity and crystallinity, and reduction of recalcitrance. During the course of hydrolysis, the cellulase dissolved the cell walls in the same manner and the digestion firstly occurred from the middle of cell walls and then toward the cell wall corners. The CLSM coupled with fluorescent labeling demonstrated that the sclerenchyma cells and vascular bundles in natural SSS were highly lignified, which caused the nonproductive bindings of cellulase on lignin. However, the efficient delignification significantly increased the accessibility and digestibility of cellulase to biomass, thereby improving the saccharification efficiency.ConclusionThis work will be helpful in investigating the biomass pretreatment and its structural characterization. In addition, the visualization results of the enzymatic hydrolysis process of pretreated lignocellulose could be used for guidance to explore the lignocellulosic biomass processing and large-scale biofuel production.

Intensification of delignification of sawdust and subsequent enzymatic hydrolysis using ultrasound.

The current work investigates intensification of delignification of sawdust and subsequent enzymatic hydrolysis to produce reducing sugars with the use of ultrasound. Alkaline hydrolysis of sawdust was initially performed to remove lignin which hampers the rate of enzymatic hydrolysis. Effect of different parameters in the case of ultrasound (US) assisted and conventional processes such as alkali concentration (0.5-2.5 N), substrate loading (0.2-1.0% w/v) and temperature (40-80 °C) have been investigated. Optimized parameters obtained for US assisted process showed better trends as compared to conventional process with about 1.25 times higher yields and significant reduction in time by about 4 h. The process parameters for US assisted and conventional enzymatic hydrolysis to produce reducing sugars were also optimized by varying substrate loading (0.5-10% w/v), reaction temperature (30-70 °C) along with variation in US power (10-80 W) and US duty cycle (30-90%). US assisted enzymatic hydrolysis performed at 4% w/v substrate loading along with 50 W US power and 50% duty cycle at 50 °C resulted in 7.46 mg/mL of reducing sugars yield within 1 h while conventional stirring with 6% w/v substrate loading and 50 °C resulted in approximately same yield of reducing sugars within 3 h. The requirement of lower time for similar yields or in other words higher yield in same time clearly highlights the process intensification benefits due to the use of ultrasound. Overall it can be concluded from the study that US assisted processes resulted in efficient delignification along with higher yield of reducing sugars in lower treatment time as compared to conventional process.

Pretreatment of cornstalk using biodegradable ionic liquid

Biodegradable ionic liquid (IL) choline acetate shows highly efficient delignification ability in cornstalk pretreatment process. Cellulose-rich products with 98% holocellulose and 2% lignin decreased from original 13% could be directly obtained from the IL-cornstalk solution by the simple, non-toxic, and green process.

The Self-Assembly of Lignin and Its Application in Nanoparticle Synthesis: A Short Review.

Lignin serves as a significant contributor to the natural stock of non-fossilized carbon, second only to cellulose in the biosphere. In this review article, we focus on the self-assembly properties of lignin and their contribution to its effective utilization and valorization. Traditionally, investigations on self-assembly properties of lignin have aimed at understanding the lignification process of the cell wall and using it for efficient delignification for commercial purposes. In recent years (mainly the last three years), an increased number of attempts and reports of technical-lignin nanostructure synthesis with controlled particle size and morphology have been published. This has renewed the interests in the self-assembly properties of technical lignins and their possible applications. Based on the sources and processing methods of lignin, there are significant differences between its structure and properties, which is the primary obstacle in the generalized understanding of the lignin structure and the lignification process occurring within cell walls. The reported studies are also specific to source and processing methods. This work has been divided into two parts. In the first part, the aggregation propensity of lignin based on type, source and extraction method, temperature, and pH of solution is discussed. This is followed by a critical overview of non-covalent interactions and their contribution to the self-associative properties of lignin. The role of self-assembly towards the understanding of xylogenesis and nanoparticle synthesis is also discussed. A particular emphasis is placed on the interaction and forces involved that are used to explain the self-association of lignin.

Efficacy of a novel sequential enzymatic hydrolysis of lignocellulosic biomass and inhibition characteristics of monosugars.

Efficient production of sugar monomers from lignocellulose is often hampered by serious bottle-necks in biomass hydrolysis. The present study reveals that ultra-sonication assisted pretreatment following autoclaving, termed as combined pretreatment, can lead to more efficient delignification of lignocellulosic biomass and an open, deformed polysaccharide matrix, found favorable for subsequent enzymatic hydrolysis, is formed. The pattern of inhibition for the enzymatic hydrolysis reaction on combined-pretreated saw dust is identified. Two main inhibition models (competitive and noncompetitive) are proposed and a better fit of experimental values with the theoretical values for the competitive inhibition model validates the proposition that in the present experiment, glucose inhibits the enzymes competitively. Additionally, accuracy of the inhibitory kinetics based models is estimated over a series of enzyme and substrate concentrations.

Structural Analysis on the Effect of Base-Catalysed Delignification Process Parameters on Palm Oil Empty Fruit Bunches Fibres using Glycome Profiling

Malaysian Oil Palm Empty Fruit Bunches (EFB) fibre was used as a model substrate and was subjected to base-catalysed delignification technique as a function of different temperature, time and base concentration. The resultant substrates were analysed using glycome profiling technique to ascertain the degree of delignification effectiveness and position of the residual lignin in the structure of the pre-treated biomass. The study indicated that the base-catalysed delignification technique removes all the outer lignin structure of the fibre due to the accessibility of the base to the surface of the biomass. Base wash concentration using sodium hydroxide (NaOH) and temperature are the two main factors that determine the effectiveness of lignin removal and increment of surface area accessibility (SAA). The pre-treated biomass that contains the lowest amount of residual lignin content of 6.19 wt.% which corresponds to 74.47% lignin removal shows complete removal of the outer layer of lignin structure but leaves the inner lignin structure intact. This study suggests that the complex interaction between different cell wall constituents plays a much bigger role in order to achieve efficient delignification.

Biorefining brewery spent grain polysaccharides through biotuning of ionic liquids

Brewery spent grain (BSG), a relevant waste from beer industry mainly composed of polysaccharides and lignin, is experiencing a surge in the production with its associated environmental impact. Thus, this manuscript bets in the application of aqueous solutions of a cholinium-based ionic liquid (IL) containing glycinate as anion ([N1112OH][Gly]) for an efficient delignification pretreatment. The operation at 90 °C yielded drastic lignin reduction (75.89%), greater than the levels attained when a traditional imidazolium-based IL (1-ethyl-3-methylimidazolium acetate, [C2C1im][C1COO]), was used (40.18%). The advantages of this pretreatment positively impacted the subsequent saccharification reaction, as the levels were increased up to about 1.5 times regarding the control (no IL) or the imidazolium-based pretreatment. ATR-FTIR spectrometry and scanning electron microscopy turned out to be useful tools to monitor the structural changes exerted. The results presented in this work make up the basis for a rational design of bio-ILs for delignification of lignocellulosic materials.

Enhanced Bioethanol Production from Waste Paper Through Separate Hydrolysis and Fermentation

The effect of various pretreatments for efficient hydrolysis of waste office paper and newspaper into fermentable sugars and subsequent production of bioethanol through fermentation was investigated. Pretreatment with H2O2 (0.5% v/v) at 121 °C for 30 min was considered as the most effective method for this kind of soft biomass like waste paper due to the considerable increase in available cellulose and sugar yield in addition to efficient delignification. Under optimized conditions, enzymatic hydrolysis of pretreated office paper and newspaper resulted the sugar yield of 24.5 and 13.26 g/L with hydrolysis efficiency of 91.8 and 79.6%, respectively. Further, ethanol production using the hydrolysate by Saccharomyces cerevisiae was about 11.15 and 6.65 g/L with the productivity of 0.32 and 0.28 (g ethanol/L/h), respectively. The improved yields achieved through the pretreatment and subsequent ethanol production suggested that the waste paper could be a potential feedstock for the production of bioethanol.