Enzymatic Hydrolysis Of Corn Stover Research Articles

Extraction, recovery, and characterization of lignin from industrial corn stover lignin cake

Lignin utilization in value-added co-products is an important component of enabling cellulosic biorefinery economics. However, aqueous dilute acid pretreatments yield lignins with limited applications due to significant modification during pretreatment, low solubility in many solvents, and high content of impurities (ash, insoluble polysaccharides). This work addresses these challenges and investigates the extraction and recovery of lignins from lignin-rich insoluble residue following dilute acid pretreatment and enzymatic hydrolysis of corn stover using three extraction approaches: ethanol organosolv, NaOH, and an ionic liquid. The recovered lignins exhibited recovery yields ranging from 30% for the ionic liquid, 44% for the most severe acid ethanol organosolv condition tested, and up to 86% for the most severe NaOH extraction condition. Finally, the fractional solubilities of different recovered lignins were assessed in a range of solvents and these solubilities were used to estimate distributions of Hildebrand and Hansen solubility parameters using a novel approach.

Improving enzymatic efficiency of β-glucosidases in cellulase system by altering its binding behavior to the insoluble substrate during bioconversion of lignocellulose

The enzymatic efficiency of β-glucosidases is influenced by their binding behavior onto insoluble substrates (cellulose and lignin) during bioconversion of lignocellulose. This study suggested that the Bgl3 protein (Aspergillus fumigatus) showed strong adsorption affinity to lignin and the Bgl1 protein (Penicillium oxalicum) tended to adsorb to cellulose. It indicated that the various surface properties of the fibronectin type Ш-like domain (FnIII) led to different binding properties of β-glucosidases by investigating their binding mechanism. By engineering β-glucosidases’ FnIII domain, Bgl3-1 and Bgl1-3 were constructed, which both showed lower binding capacities to insoluble substrates. As well as for Bgl1-3, its sensitivity to the phenolic component was also eased. Based on that, the reconstructed protein showed high catalytic efficiency during the enzymatic hydrolysis of corn stover by effectively transforming cellobiose to glucose. Thus, this study provided a new strategy to engineer β-glucosidases to enhance their performance in the cellulase system.

Effect of pelleting on the enzymatic digestibility of corn stover

Pelleting of lignocellulosic biomass to improve its transportation, storage and handling impacts subsequent processing and conversion. This work reports the role of high moisture pelleting in the enzymatic digestibility of corn stover prior to pretreatment, together with associated substrate characteristics. Pelleting increases the digestibility of unpretreated corn stover, from 8.2 to 15.5% glucan conversion, at 5% solid loading using 1 FPU Cellic® CTec2 per g solids. Compositional analysis indicates that loose and pelleted corn stover have similar non-dissolvable compositions, although their extractives are different. Enzymatic hydrolysis of corn stover after size reduction to normalize particle sizes and removal of extractives confirms that pelleting improves corn stover digestibility. Such differences may be explained by the decreased particle size, improved substrate accessibility, and hydrolysis of cross-linking structures induced by pelleting. These findings are useful for the development of processing schemes for sustainable and efficient use of lignocellulose.

Simultaneous pretreatment with ultraviolet light and alkaline H2O2 to promote enzymatic hydrolysis of corn stover

Pretreatment processes are essential for the preparation of biofuels from lignocellulosic feedstocks. Based on alkaline H2O2 pretreatment, photocatalytic alkaline H2O2 pretreatment (U-AHP) was investigated to examine the effects of reaction time, alkali concentration, and H2O2 concentration on the enzymatic digestion of corn stover. The optimum process conditions were determined by orthogonal tests: 1% NaOH, 2% H2O2, and reaction time of 8 h. Under these conditions, the lignin removal efficiency of UH-AHP was 90.2% and the saccharification yield was 94.7%. Furthermore, FT-IR, XRD, and SEM analyses showed that U-AHP pretreatment caused structural damage to the maize straw and increased the crystallinity of the cellulose, and it was speculated that the U-AHP pretreatment reaction was a complex mechanism, which might be a multiple synergistic reaction. This study shows that U-AHP pretreatment is a simple, green and effective method to promote lignin removal.

Low-temperature EDA/urea pretreatment improves enzymatic hydrolysis of corn stover through changing physical and chemical structure

Low-temperature EDA/urea pretreatment improves enzymatic hydrolysis of corn stover through changing physical and chemical structure

Construction of novel cellulase with high activity, great stability and excellent lignin-resistant for efficient enzymatic hydrolysis by hydrophilic and negatively charged modification

The lignin-derived inhibition on cellulase is the most critical bottleneck that must be addressed when converting lignocellulosic biomass through the sugar-platform process. Herein, a novel modified cellulase with high activity, great stability and excellent lignin-resistant ability was synthesized by chemical modification using hydrophilic and negatively charged polyethylene glycol (PEG) derivatives including HO-PEG-COOH and HOOC-PEG-COOH. Both modifications obviously increased the cellulase activity, with 37% (HO-PEG-COOH modification) and 53% (HOOC-PEG-COOH modification) increase, respectively. In addition, the stabilities of both modified cellulases were significantly enhanced, seeing from their much higher activities at all selected temperatures and pH values. The modification resulted in a movement of tryptophan residues to the exterior of enzyme, allowing the substrate chains to be more easily recruited and thus initiating the hydrolysis. The compactness of secondary structure for enzyme was improved, especially, the α-helix content was increased which requires strong hydrogen bonding to generate it, thus enhancing the stability. High hydrophilicity, negative charge and compactness of enzyme conferred modified cellulase good ability to resist lignin adsorption and destruction, thus improving the enzymatic hydrolysis of corn stover. • Cellulase activity is significantly improved by up to 52% after chemical modification. • The migration of Trp residues allows the hydrolysis to be more easily initiated. • High compactness gives modified cellulase great stability and low level of damage by lignin. • High hydrophilicity and negative charge of modified cellulase prevent lignin adsorption. • The novel modified cellulase exhibits promising potential in converting corn stover.

A new l-cysteine-assisted glycerol organosolv pretreatment for improved enzymatic hydrolysis of corn stover

Deconstruction of lignocellulose via efficient pretreatment is crucial for producing fermentable sugars. In this study, effects of glycerol organosolv pretreatment (GOP) on main chemical composition of corn stover were investigated. Results indicate that the residual corn stover after 80 wt% glycerol pretreatment (at 220 °C for 0.5 h) yielded 75.97 % glucose and 78.21 % xylose after enzymatic hydrolysis, which were enhanced by 3.39- and 6.08-fold compared to the untreated corn stover. Subsequently, an l-cysteine-assisted GOP was proposed with higher yields of glucose (86.20 %) and xylose (91.13 %). When pretreating corn stover with 80 wt% glycerol containing 0.07 wt% l-cysteine at 220 °C for 0.5 h, higher fermentable sugars of 26.08 g were produced from 100 g feedstock after enzymolysis. Intrinsic mechanisms of the proposed pretreatment for enhancing enzymatic digestibility were elucidated by physiochemical characterization technologies and techno-economic analysis was also studied. This study provides guidance for fermentable sugars production from renewable lignocellulose.

Enhanced enzymatic hydrolysis of corn stover using twin‐screw extrusion under mild conditions

AbstractThis paper aims to investigate the effect of extrusion at high solid loading on corn stover (CS) properties and its enzymatic hydrolysis. This biomass was extruded under different screw speeds and different solid loadings and the impact of these parameters on the physicochemical properties was evaluated. It was found that lignocellulosic components were not significantly affected by the pretreatment, while the surface area increased with solid loading and rotation speed. Different enzyme cocktails were used for the enzymatic hydrolysis of extruded and untreated CS. Overall, mild twin‐extrusion enhanced the enzymatic hydrolysis of CS through an increase in glucose and xylose yields by 134–212% and 214–294%, respectively, when using Trichoderma longibrachiatum cellulase. The highest sugar content was obtained from CS extruded under 400 g total solids per liter and 200 rpm. The energy efficiency of the pretreatment was also assessed and was found to be maximal at 400 g total solids per liter and 200 rpm. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Pretreatment of Corn Stover by Levulinic Acid-Based Protic Ionic Liquids for Enhanced Enzymatic Hydrolysis

Economically competitive and sustainable dissolution pretreatment technology is in high demand due to the remarkable achievement in the pretreatment of lignocellulose using ionic liquids (ILs) for enhanced enzymatic hydrolysis. Herein, levulinic acid (Lev), a well-known bio-based platform chemical derived from carbohydrates, in conjunction with a series of organic superbases, was used as a raw chemical to prepare a new class of protic ILs (PILs). The findings indicated that the obtained PILs exhibited a good solubility of up to 10 wt % toward corn stover-based lignocellulose at 140 °C in 40 mins, based on which a facile and efficient dissolution pretreatment technology was developed for enhanced enzymatic hydrolysis of corn stover. The facile dissolution and regeneration of corn stover resulted in significant changes in the composition and physical–chemical structures. These changes led to significantly enhanced enzymatic hydrolysis behavior of the pretreated sample with total reducing sugar and glucose yields of 0.8 and 0.49 g/g within 48 h under optimal conditions, respectively. The Kamlet–Taft solvent parameters of the PILs were systematically evaluated, and the interaction between the lignocellulose and PILs was studied by 13C NMR, indicating that the satisfactory performance of PILs was benefited from the higher ß parameter value and the stronger interactions, particularly the existence of the extra hydrogen-bond interaction from the potential keto–enol tautomerism of the ketone groups in levulinate anions. The compositional and physicochemical changes in the lignocellulose were systematically evaluated to achieve an in-depth understanding of the dissolution activation mechanism using various characterization techniques. The findings also showed that 44.3% of lignin could be fractionated during the facile dissolution and regeneration process, together with a transformation of the crystalline structure of cellulose I to cellulose II and of the packed morphology to a porous one. The structure of the fractionated lignin was also characterized for a better understanding of the fractionation process. The study demonstrated a new sustainable dissolution pretreatment technology for enhanced enzymatic hydrolysis, which can provide significant insights into the design of new solvents for biomass dissolution and processing.

Effect of combined wet alkaline mechanical pretreatment on enzymatic hydrolysis of corn stover and its mechanism

BackgroundTo further optimize the mechanochemical pretreatment process, a combined wet alkaline mechanical pretreatment of corn stover was proposed with a short time and less chemical consumption at room temperature.ResultsThe combined alkaline mechanical pretreatment significantly enhanced enzymatic hydrolysis resulting a highest glucose yield (YG) of 91.9% with 3% NaOH and ball milling (BM) for 10 min. At this optimal condition, 44.4% lignin was removed and major portion of cellulose was retained (86.6%). The prehydrolysate contained by-products such as monosaccharides, oligosaccharides, acetic acid, and lignin but no furfural and 5-HMF. The alkaline concentration showed a significant impact on glucose yield, while the BM time was less important. Quantitative correlation analysis showed that YG (%) = 0.68 × BM time (min) + 19.27 × NaOH concentration (%) + 13.71 (R2 = 0.85), YG = 6.35 × glucan content − 231.84 (R2 = 0.84), and YG = − 14.22 × lignin content + 282.70 (R2 = 0.87).ConclusionThe combined wet alkaline mechanical pretreatment at room temperature had a boosting effect on the yield of enzymatic hydrolysis with short treatment time and less chemical consumption. The impact of the physical and chemical properties of corn stover pretreated with different BM times and/or different NaOH concentrations on the subsequent enzymatic hydrolysis was investigated, which would be beneficial to illustrate the effective mechanism of the mechanochemical pretreatment method.

Pretreatment Affects Profits From Xylanase During Enzymatic Saccharification of Corn Stover Through Changing the Interaction Between Lignin and Xylanase Protein.

Effective pretreatment is vital to improve the biomass conversion efficiency, which often requires the addition of xylanase as an accessory enzyme to enhance enzymatic saccharification of corn stover. In this study, we investigated the effect of two sophisticated pretreatment methods including ammonium sulfite (AS) and steam explosion (SE) on the xylanase profits involved in enzymatic hydrolysis of corn stover. We further explored the interactions between lignin and xylanase Xyn10A protein. Our results showed that the conversion rates of glucan and xylan in corn stover by AS pretreatment were higher by Xyn10A supplementation than that by SE pretreatment. Compared with the lignin from SE pretreated corn stover, the lignin from AS pretreated corn stover had a lower Xyn10A initial adsorption velocity (13.56 vs. 10.89 mg g−1 min−1) and adsorption capacity (49.46 vs. 27.42 mg g−1 of lignin) and weakened binding strength (310.6 vs. 215.9 L g−1). Our study demonstrated the low absolute zeta potential and strong hydrophilicity of the lignin may partly account for relative weak interaction between xylanase protein and lignin from AS pretreated corn stover. In conclusion, our results suggested that AS pretreatment weakened the inhibition of lignin to enzyme, promoted the enzymatic hydrolysis of corn stover, and decreased the cost of enzyme in bioconversion.

Effects of soaking aqueous ammonia pretreatment on chemical composition and enzymatic hydrolysis of corn stover

Effects of soaking aqueous ammonia pretreatment on chemical composition and enzymatic hydrolysis of corn stover. The aim of this research was to investigate the effect of applying two different temperatures of the soaking aqueous ammonia treatment on the chemical composition and enzymatic hydrolysis yield of the corn stover. Native corn stover as well as solid fractions after 20 h of alkali pretreatment performed at 15% ammonia solution and at 50 °C or 90 °C were analysed in terms of cellulose, holocellulose, lignin and extractives content. Both untreated and treated samples were subjected to the enzymatic hydrolysis and hydrolysates were examined with a high performance liquid chromatography (HPLC). Results indicated a significant development of enzymatic digestibility of the SAA treated biomass. Furthermore, a 38.7% and a 68.9% delignification levels in the biomass treated with ammonia at respectively 50 °C and 90 °C process comparing to the raw material were achieved.

Study on ionic liquid treatment and enzymatic hydrolysis of corn stover after activation of zinc chloride solution

With the intensification of the energy crisis, this thesis uses corn stalk cellulose as the raw material to carry out research on biomass energy. By designing the response surface experiment, a multiple quadratic regression equation prediction model of the response surface factors and the yield of enzymatic reducing sugars after the activation of the zinc chloride solution treated by the ionic liquid was established, which provided the technology for the ionic liquid treatment of the metal ion solution to activate the corn stalk raw materia reference. The experimental results show that the yield of enzymatically hydrolyzed reducing sugars of corn stalks after being activated by metal ions and then treated with ionic liquids is greatly improved compared to the raw materials.

Alkaline pretreatment and enzymatic hydrolysis of corn stover for bioethanol production

The demand for ethanol in Brazil is growing. However, although the country is one of the largest producers of this fuel, it is still necessary to diversify the production matrix. In that regard, studies with different raw materials are needed, mainly the use of low cost and high available wastes such as lignocellulosic residues from agriculture. Therefore, this study aimed to analyze the bioethanol production from corn stover. An alkaline pretreatment (CaO) was carried out, followed by enzymatic hydrolysis (Cellic Ctec2 and Cellic Htec2) to obtain fermentable sugars. The best experimental condition for the pretreatment and hydrolysis steps resulted in a solution with 0.31 gsugar∙gbiomass-1. Then, the fermentation was performed by the industrial strain of Saccharomyces cerevisiae (PE-2) and by the wild yeast strain Wickerhamomyces sp. (UFFS-CE-3.1.2). The yield obtained was 0.38 gethanol∙gdry biomass-1 was, demonstrating the potential of this process for bioethanol production.

Potassium permanganate assisted organosolv pretreatment enhances enzymatic hydrolysis of corn stover

AbstractHigh efficiency enzymatic hydrolysis of lignocellulose to produce fermentable sugar is important for bioconversion of lignocellulosic biomass to liquid fuels and chemicals. In this study, a simple pretreatment with potassium permanganate is used to enhance the efficiency of organosolv pretreatment of corn stover. It is testified that, compared to the single organosolv pretreatment, the KMnO4 assisted organosolv pretreatment significantly increase yields of carbohydrates through decreasing degradation of hemicellulose, decrease formation of inhibitors and enhance enzymatic hydrolysis of corn stover pretreated at a low pretreatment temperature. Process conditions of the KMnO4 assisted organosolv pretreatment are optimized and the conversion of glucan and xylan in pretreated corn stover at 72 h of enzymatic hydrolysis reach to 89.45% and 85.30% respectively when corn stover is firstly treated with 1% (w/w) KMnO4 at 40°C for 60 min prior to ethanol‐water pretreatment with 50% ethanol concentration at 185°C for 90 min. The differences in morphological feature, fiber surface chemical compositions, crystallinity degree and thermostability of pretreated corn stover by ethanol‐water with and without KMnO4 are characterized by scanning electron microscope, X‐ray photoelectron spectroscopy, X‐ray diffraction and thermogravimetry to explore the underlying reasons of KMnO4 strengthening ethanol‐water pretreatment process.

Effects of milling combined with extremely low-liquid ammonia (ELLA) pretreatment to enhance enzymatic hydrolysis of corn stover

Lignocellulosic biomass is one of the largest carbohydrate sources and has huge potential for biofuels production. However, the problem with lignocellulosic feedstock is that it has useful sugars locked in by lignin, hemicellulose, and cellulose. Some kind of pretreatment; therefore is needed to make carbohydrate accessible which later can be fermented to produce ethanol. The results from this research indicated that the yields of glucan (93%) and xylan (82.8%) were improved by using milling combined with ELLA pretreatment. The optimal enzymatic hydrolysis efficiencies were obtained under 10 min for ball milling time, pretreatment at 1 h, temperature at 150°C, S/L = 0.5 and ammonia loading at 0.25 g-NH3/g-biomass. This method reduced the pretreatment time and short milling time and thus has potential of reducing the energy consumption and promising the application in the large scale.

Two Nonnegligible Factors Influencing Lignocellulosic Biomass Valorization: Filtration Method after Pretreatment and Solid Loading during Enzymatic Hydrolysis

Valorization of lignocellulosic biomass into biofuels has received considerable attention for decades with tremendous thermochemical pretreatments proposed. However, inconsistencies among studies in lignin removal can often be misleading and even violate the chemical mechanism, which might be attributed to the variation in the filtration method used after pretreatment. A phenomenon, promoting pretreatment strategies based on sugar conversion efficiency or yield only from single and random low-solid enzymatic hydrolysis, was also observed. Herein, the effects of filtration methods using a slow drip metal filter (SDMF) with an aperture of 0.2 mm and Whatman grade 4 filter paper (WGFP) with an aperture of 20–25 μm under vacuum filtration after liquid hot water (LHW), acid, and alkali pretreatments on the chemical composition of the solid and liquid, sugar recoveries, and lignin removal and solid loading (2–15%) on enzymatic hydrolysis of corn stover and poplar wood were investigated. Results showed that SDMF increased the glucan content (1.1–3.0%) in pretreated biomass and induced solid loss (3.8–12.6%) into the filtrates, resulting in lower sugar recoveries and overestimated lignin removal compared to WGFP. 5-Hydroxymethylfurfural (HMF) and furfural derived from sugar degradation triggered pseudolignin formation, inducing a negative lignin removal for both LHW and acid pretreated biomass. In comparison, alkali pretreatment neutralized the weak acids released from sugar decomposition and achieved a robust delignification (67.8–90.8%). Solid loading used for enzymatic hydrolysis of pretreated biomass determined sugar concentration, conversion efficiency, and yield. This result indicates that promoting pretreatment technologies based on sugar conversion efficiency or yield of enzymatic hydrolysis at low solid loading may be misleading. This work demonstrates that the filtration method used for solid and liquid separations after pretreatment and solid loading for enzymatic hydrolysis should be cautiously selected and implemented when valorizing biomass into biofuels.

Mild Urea/KOH pretreatment to enhance enzymatic hydrolysis of corn stover with liquid waste recovery for plant growth

Alkaline pretreatment can effectively remove lignin and significantly increase enzymatic hydrolysis efficiency of lignocellulosic biomass. Sodium hydroxide (NaOH) is the common alkali for treating lignocellulose. However, a large quantity of liquid waste (LW) generated in the NaOH pretreatment process is hard to be removed. In this context, this work employed KOH together with urea for treating corn stover (CS) and explored the feasibility of recovering LW for plant fertilization due to the existence of potassium (K) and nitrogen (N) elements in LW. With response surface methodology, an optimum pretreatment condition, which was 1:1 (2% w/v) Urea/KOH (UK) at 30 °C for 2 h was achieved. Enzymatic digestibility of UK-treated CS could attain 75.49%, which was 12.55% higher than that of KOH-treated CS under the same conditions. The glucose yield could be further increased to 83.1% with the addition of 1% Tween-80. Meanwhile, the LW showed significant enhancement in the length and biomass yield of two cereal and three vegetable crops. UK pretreatment is a promising greenway for cellulosic ethanol production by recycling LW as value-added fertilizer.

Glycerol-assisted one-step instant catapult steam explosion enhances enzymatic digestibility of corn stover

Glycerol-assisted one-step instant catapult steam explosion (ICSE) was studied for corn stover pretreatment. Glycerol addition reduced lignin content from ∼32 % to ∼24 % in pretreated solid residues with a stover/glycerol ratio from 1:0.0 to 1:2.0. Glycerol addition might help to reduce the formation of pseudo-lignin with the reduction of the total lignin recovered in pretreated solid residue from 114 % (possibly because of pseudo-lignin contribution) to 81 %. Furthermore, atomic forced microscopy analysis showed that glycerol addition improved surface roughness of pretreated corn stover. Moreover, it was proposed that glycerol-assisted ICSE likely led to the reactions of glycerol with lignin and lignin-derivatives through α-etherification and γ-esterification, preserving lignin internal β-O-4 linkages and preventing lignin condensation. Finally, enzymatic hydrolysis of corn stover pretreated by glycerol-assisted ICSE at a stover/glycerol ratio of 1:1 led to a glucan digestibility in solid residues of 98.4 % and a glucose yield of 79.3 %, which were 27.9 % and 44.7 % higher than those without glycerol addition, respectively.

Ammonia Fiber Expansion (AFEX) Pretreatment of Lignocellulosic Biomass.

Lignocellulosic materials are plant-derived feedstocks, such as crop residues (e.g., corn stover, rice straw, and sugar cane bagasse) and purpose-grown energy crops (e.g., miscanthus, and switchgrass) that are available in large quantities to produce biofuels, biochemicals, and animal feed. Plant polysaccharides (i.e., cellulose, hemicellulose, and pectin) embedded within cell walls are highly recalcitrant towards conversion into useful products. Ammonia fiber expansion (AFEX) is a thermochemical pretreatment that increases accessibility of polysaccharides to enzymes for hydrolysis into fermentable sugars. These released sugars can be converted into fuels and chemicals in a biorefinery. Here, we describe a laboratory-scale batch AFEX process to produce pretreated biomass on the gram-scale without any ammonia recycling. The laboratory-scale process can be used to identify optimal pretreatment conditions (e.g., ammonia loading, water loading, biomass loading, temperature, pressure, residence time, etc.) and generates sufficient quantities of pretreated samples for detailed physicochemical characterization and enzymatic/microbial analysis. The yield of fermentable sugars from enzymatic hydrolysis of corn stover pretreated using the laboratory-scale AFEX process is comparable to pilot-scale AFEX process under similar pretreatment conditions. This paper is intended to provide a detailed standard operating procedure for the safe and consistent operation of laboratory-scale reactors for performing AFEX pretreatment of lignocellulosic biomass.