Enhanced enzymatic hydrolysis of triploid poplar following stepwise acidic pretreatment and alkaline fractionation

Exploration of deep eutectic solvent-based biphasic system for furfural production and enhancing enzymatic hydrolysis: Chemical, topochemical, and morphological changes

Developing a biorefinery process for a highly integrated valorization and fractionation of lignocellulose is crucial for its utilization. Herein, a biphasic system comprising choline chloride/lactic acid and 2-methyltetrahydrofuran with Al₂(SO₄)₃ and H₂SO₄ as catalysts was applied to pretreat Eucalyptus. Results showed that under the optimized conditions (150 °C, 30 min, 0.2 M Al₂(SO₄)₃, 0.075 M H₂SO₄), the furfural yield and enzymatic hydrolysis efficiency could reach 54.7% and 97.0%, respectively. The efficient cellulose conversion was attributed to remarkable removal of lignin (91.0%) and hemicelluloses (100.0%), thereby causing the disruption of cell wall structure and enhancement of cellulose accessibility. Meanwhile, confocal Raman microscope and atomic force microscope displayed that the pretreatment resulted in the decreasing intensities of carbohydrates and lignin different regions of cell walls, and exposing of the embedded microfibers from noncellulosic polymers. Overall, the deep eutectic solvent-based biphasic system displayed high performance for effective utilization of carbohydrate components in lignocellulose.

Structural Changes in Milled Wood Lignin (MWL) of Chinese Quince (Chaenomeles sinensis) Fruit Subjected to Subcritical Water Treatment

Subcritical water treatment has received considerable attention due to its cost effectiveness and environmentally friendly properties. In this investigation, Chinese quince fruits were submitted to subcritical water treatment (130, 150, and 170 °C), and the influence of treatments on the structure of milled wood lignin (MWL) was evaluated. Structural properties of these lignin samples (UL, L130, L150, and L170) were investigated by high-performance anion exchange chromatography (HPAEC), FT-IR, gel permeation chromatography (GPC), TGA, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), 2D-Heteronculear Single Quantum Coherence (HSQC) -NMR, and 31P-NMR. The carbohydrate analysis showed that xylose in the samples increased significantly with higher temperature, and according to molecular weight and thermal analysis, the MWLs of the pretreated residues have higher thermal stability with increased molecular weight. The spectra of 2D-NMR and 31P-NMR demonstrated that the chemical linkages in the MWLs were mainly β-O-4' ether bonds, β-5' and β-β', and the units were principally G- S- H- type with small amounts of ferulic acids; these results are consistent with the results of Py-GC/MS analysis. It is believed that understanding the structural changes in MWL caused by subcritical water treatment will contribute to understanding the mechanism of subcritical water extraction, which in turn will provide a theoretical basis for developing the technology of subcritical water extraction.

Effects of sodium and calcium chloride ionic stresses on model yeast membranes revealed by molecular dynamics simulation

As efforts to move a renewable economy grow, it will be necessary to make use of microbial conversion strategies for the production of novel materials or the upgrading of waste to high-value products. One critical technical challenge currently limiting waste upgrading remains the difficulty in obtaining single-pot conversion techniques where physical, chemical, and biological conversion are performed in a single step. To overcome this challenge, a detailed understanding of how different stresses impact microbial membrane stability will be necessary. Using all-atom molecular dynamics simulations, we examine the impacts of moderate concentrations of NaCl and CaCl₂on a model yeast plasma membrane. Weak, though statistically significant, changes in membrane morphology and dynamics functions are observed that are consistent with swelling and stiffening. Additionally, an examination of the ion-lipid contacts and the behavior of water at the water-membrane interface suggests that the impacts of these common salts may, in part, be mediated through changes to water-membrane hydrogen-bonding and hydration water dynamics.

Assessment on temperature-pressure severally controlled explosion pretreatment of poplar

In this work, temperature-pressure severally controlled explosion pretreatment (TPE) was proposed to pretreat poplar chips to improve the cellulase hydrolysis yield. In TPE process, native poplar chips (NP) were mixed with steam and N₂ under pressure of 2.6, 2.8 and 3.0 MPa at 209 °C for 7 min. Meanwhile, steam explosion (SE) was also used to pretreat poplar chips for comparison at 209 °C (1.9 MPa) for 7 min. Results showed that the contents of hemicellulose and lignin were decreased from 19.4 % to 4.6 % and from 27.8 %-19.5 % with increasing pressure, respectively. For cellulase hydrolysis process, TPE was more advantageous than SE due to lower contents of hemicellulose and lignin, resulting in a higher cellulose conversion (40.7 %) in relation to SE sample (34.9 %). The Langmuir isothermal- type equation expressed the factors related to the hydrolysis capacity, and the results showed that this model can well describe the kinetics of the enzymatic hydrolysis.

Improved ethanol production from the slurry of pretreated brewers' spent grain through different co-fermentation strategies

The aim of this work was to bioconvert all sugars in BSG into ethanol using a process scheme that includes the enzymatic hydrolysis of the whole slurry resulting from the pretreatment of BSG with phosphoric and sulfuric acid using previously optimised conditions, followed by the co-fermentation of the mixed sugars. More than 90% of the sugars in raw BSG were recovered in the pretreatment and the subsequent enzymatic hydrolysis of the whole slurry. The co-fermentation of the enzymatic hydrolysates with Escherichia coli was then compared with that the co-culture of Scheffersomyces stipitis and Saccharomyces cerevisiae, which resulted in lower ethanol production. The co-fermentation strategy with a single microorganism (E. coli) when BSG was pretreated with phosphoric acid resulted into the highest ethanol concentration, 39 g/L, which means that 222 L of ethanol can be obtained from a ton of BSG without detoxification requirements.

Hydrogen Production from Energy Poplar Preceded by MEA Pre-Treatment and Enzymatic Hydrolysis

The need to pre-treat lignocellulosic biomass prior to dark fermentation results primarily from the composition of lignocellulose because lignin hinders the processing of hard wood towards useful products. Hence, in this work a two-step approach for the pre-treatment of energy poplar, including alkaline pre-treatment and enzymatic saccharification followed by fermentation has been studied. Monoethanolamine (MEA) was used as the alkaline catalyst and diatomite immobilized bed enzymes were used during saccharification. The response surface methodology (RSM) method was used to determine the optimal alkaline pre-treatment conditions resulting in the highest values of both total released sugars (TRS) yield and degree of lignin removal. Three variable parameters (temperature, MEA concentration, time) were selected to optimize the alkaline pre-treatment conditions. The research was carried out using the Box-Behnken design. Additionally, the possibility of the re-use of both alkaline as well as enzymatic reagents was investigated. Obtained hydrolysates were subjected to dark fermentation in batch reactors performed by Enterobacter aerogenes ATCC 13048 with a final result of 22.99 mL H₂/g energy poplar (0.6 mol H₂/mol TRS).

Pretreatment of Lignocellulosic Materials as Substrates for Fermentation Processes

Lignocellulosic biomass is an abundant and renewable resource that potentially contains large amounts of energy. It is an interesting alternative for fossil fuels, allowing the production of biofuels and other organic compounds. In this paper, a review devoted to the processing of lignocellulosic materials as substrates for fermentation processes is presented. The review focuses on physical, chemical, physicochemical, enzymatic, and microbiologic methods of biomass pretreatment. In addition to the evaluation of the mentioned methods, the aim of the paper is to understand the possibilities of the biomass pretreatment and their influence on the efficiency of biofuels and organic compounds production. The effects of different pretreatment methods on the lignocellulosic biomass structure are described along with a discussion of the benefits and drawbacks of each method, including the potential generation of inhibitory compounds for enzymatic hydrolysis, the effect on cellulose digestibility, the generation of compounds that are toxic for the environment, and energy and economic demand. The results of the investigations imply that only the stepwise pretreatment procedure may ensure effective fermentation of the lignocellulosic biomass. Pretreatment step is still a challenge for obtaining cost-effective and competitive technology for large-scale conversion of lignocellulosic biomass into fermentable sugars with low inhibitory concentration.

Epoxidation and etherification of alkaline lignin to prepare water-soluble derivatives and its performance in improvement of enzymatic hydrolysis efficiency

BACKGROUND

Due to the depletion of fossil resources and their environmental impact, woody biomass has received much attention as an alternative resource. Lignin, as the third most abundant biopolymer from biomass, is now considered as an excellent alternative feedstock for chemicals and materials. The conversion of lignin to the value-added products is a key process to achieve an integrated biorefinery of woody biomass. Among these value-added products, lignin-based derivatives with good surface activity can be applied to enhance the conversion of cellulose into fermentable sugars, which not only decrease the cost of bioethanol production, but also reduce the environmental pollution and green house effect resulting from the burning of fossil resources.

RESULTS

Water-soluble alkaline lignin was synthesized by the reaction between polyethylene glycols (PEG600 and PEG1000) and epoxy lignin. FT-IR and NMR analyses indicated that PEGs were successively introduced into epoxy alkaline lignin using potassium persulfate as a catalyst. Emulsification and surface activity tests indicated that the surface tension of the prepared lignin derivative solution was 43.30 mN/m at the critical micelle concentration (1.03 %). A stable emulsions layer was formed with hexanes and the emulsion particle diameter in the emulsion phase for all products was observed at 10-50 μm. The results of enzymatic hydrolysis indicated that the products derived from PEG1000-grafted lignin resulted in the highest increasing rate of 18.6 % of glucose yield during the enzymatic hydrolysis of hardwood bleached pulp. The results of fermentation experiments suggested that the product had no toxicity for fermentation micro-organisms.

CONCLUSION

Water-soluble alkaline lignin derivatives were prepared through epoxidation and etherification, which are promising feedstocks for detergents, emulsifier, and additive to enhance enzymatic hydrolysis efficiency and ethanol fermentation.

Effects of aluminum chloride-catalyzed hydrothermal pretreatment on the structural characteristics of lignin and enzymatic hydrolysis

In this study, Eucalyptus camaldulensis was pretreated with 0.02 M aluminum chloride (AlCl3) at 140-180 °C to obtain digestible substrates for glucose and lignin. The effects of AlCl3-catalyzed hydrothermal pretreatment on the degradation of carbohydrates, structural changes of lignin, crystallinity, morphologic changes, and cellulose conversion of the pretreated biomass have been investigated by HAPEC, HPLC, FT-IR, XRD, CP/MAS NMR, SEM, and 2D-HSQC NMR. Results showed that the pretreatment significantly removed hemicelluloses and cleaved β-O-4 linkages of lignin at high temperatures. Under an optimum condition (at 170 °C for 1 h), almost all of hemicelluloses were removed and most of β-O-4 linkages in lignin were cleaved, and 77.8% cellulose conversion of the pretreated biomass was achieved, which was 7.3-fold higher than that of the original biomass. In short, this process was regarded as a promising approach to achieve an efficient conversion of lignocellulosic biomass to fermentable glucose and residual lignin.

Characteristics and enzymatic hydrolysis of cellulose-rich fractions from steam exploded and sequentially alkali delignified bamboo (Phyllostachys pubescens)

In this study, cellulose-rich fractions from bamboo were prepared with steam explosion pretreatment (SEP) followed by a successive alkaline delignification to improve the enzymatic digestibility for an efficient bioethanol production. The cellulose-rich fractions obtained were characterized by FT-IR, XRD, CP/MAS (13)C NMR, SEM, and BET surface area. It was found that the SEP alone significantly removed partial hemicelluloses, while the synergistic treatment by SEP and alkaline delignification removed most hemicelluloses and lignin. Results from enzymatic hydrolysis showed that SEP alone improved the enzymatic hydrolysis rate by 7.9-33.1%, while the synergistic treatment by SEP and alkaline delignification enhanced the rate by 45.7-63.9%. The synergistic treatment by SEP at 2.0 MPa for 5 min with water impregnation followed by a successive alkaline delignification with 0.5% NaOH and 70% ethanol containing 1.5% NaOH resulted in a maximum enzymatic hydrolysis rate of 70.6%.

Enhanced enzymatic hydrolysis of bamboo (Dendrocalamus giganteus Munro) culm by hydrothermal pretreatment

Bamboo was non-isothermally pretreated with hot water at 140-200°C for different times (10-120 min). The effects of pretreatment conditions on the degradation of carbohydrates, cellulose crystallinity, partial removal/relocation of lignin, morphologic change of the feedstock, and glucose yield during the enzymatic hydrolysis were investigated. The effective removal of amorphous cellulose and hemicelluloses led to the increase of crystalline index of the residues. In comparison with the raw material, the surface of the pretreated samples was irregular and numerous lignin droplets appeared on the cellulose bundle surface under the intense pretreatment conditions. The glucose conversion increased with the raise of pretreatment temperature and the prolongation of time, and the maximum conversion of 75.7% was achieved for the sample pretreated at 200°C for 120 min, whereas the untreated sample was only 15.7%. The result illustrated that hydrothermal pretreatment affected the composition of bamboo, and remarkably enhanced the enzymatic hydrolysis efficiency.

Improving the enzymatic hydrolysis of thermo-mechanical fiber from Eucalyptus urophylla by a combination of hydrothermal pretreatment and alkali fractionation

BACKGROUND

The recalcitrance of lignocellulosic biomass is a major limitation for its conversion into biofuels by enzymatic hydrolysis. The use of a pretreatment technology is an essential step to diminish biomass recalcitrance for bioethanol production. In this study, a two-step pretreatment using hydrothermal pretreatment at various temperatures and alkali fractionation was performed on eucalyptus fiber. The detailed chemical composition, physicochemical characteristics, and morphology of the pretreated fibers in each of the fractions were evaluated to advance the performance of eucalyptus fiber in enzymatic digestibility.

RESULTS

The hydrothermal pretreatment (100 to 220°C) significantly degraded hemicelluloses, resulting in an increased crystallinity of the pretreated fibers. However, as the pretreatment temperature reached 240°C, partial cellulose was degraded, resulting in a reduced crystallinity of cellulose. As compared to the hydrothermal pretreatment alone, a combination of hydrothermal and alkali treatments significantly removed hemicelluloses and lignin, resulting in an improved enzymatic hydrolysis of the cellulose-rich fractions. As compared with the raw fiber, the enzymatic hydrolysis rate increased 1.1 to 8.5 times as the hydrothermal pretreatment temperature increased from 100 to 240°C. Interestingly, after a combination of hydrothermal pretreatment and alkali fractionation, the enzymatic hydrolysis rate increased 3.7 to 9.2 times. Taking into consideration the consumption of energy and the production of xylo-oligosaccharides and lignin, an optimum pretreatment condition was found to be hydrothermal pretreatment at 180°C for 30 min and alkali fractionation with 2% NaOH at 90°C for 2.5 h, in which 66.3% cellulose was converted into glucose by enzymatic hydrolysis.

CONCLUSIONS

The combination of hydrothermal pretreatment and alkali fractionation was a promising method to remove hemicelluloses and lignin as well as overcome the biomass recalcitrance for enzymatic hydrolysis from eucalyptus fiber. In addition, the various techniques applied in this work constituted an efficient approach to understand the underlying chemical and morphological changes of the cellulose-rich fractions.

Sodium sulfite-formaldehyde pretreatment of mixed hardwoods and its effect on enzymatic hydrolysis

In this work, mixed hardwoods were pretreated by sodium sulfite-formaldehyde (SF). The effects of SF pretreatment on the chemical compositions and enzymatic hydrolysis of mixed hardwoods were investigated. SF pretreatment temperature had a significant effect on pulp yield and delignification, resulting in an increased efficiency of enzymatic hydrolysis. After 96 h of enzymatic hydrolysis at the cellulase loading of 40 FPU/g substrate, the yields of glucan and xylan on the basis of original wood were 37% and 11% for the pulp produced with 12% sulfite charge at 170 °C for 2 h. The total sugar recovery based on the sugar in original wood was 74%. These results indicate that sulfite-formaldehyde cooking is of great potential to be a pretreatment method for a greenfield mill to produce fuel ethanol from hardwood.

Structural transformation of hemicelluloses and lignin from triploid poplar during acid-pretreatment based biorefinery process

In order to understand the behaviors of hemicelluloses and lignin under the given acidic conditions with increasing severity, the structural characteristics were elucidated in detail by both wet chemistry methods and spectroscopic analyses in this study. Although acidic pretreatment significantly hydrolyzed the glycosidic linkages in xylan backbone and then reduced the molecular weight of xylan from 89,600 to 19,630 g/mol, a slightly increased amount of glucuronic acid was observed, probably attributing to the maintenance of ester bonds. The serious structural variation occurred in lignin macromolecule was evidenced by the extensive degradation of β-O-4 ether linkages and resinol substructure, together with the changes in the ratios of the three monolignols in ester-bond, ether-bond and non-condensed phenolic compounds. At the most severity, obvious condensation reactions introduced the clear shift of C(2) and C(5) correlations and the absence of C(6) correlation in guaiacyl units by 2D HSQC analysis.