Pretreatment of Eucalyptus in biphasic system for furfural production and accelerated enzymatic hydrolysis

An integrated biorefinery strategy for Eucalyptus fractionation and co-producing glucose, furfural, and lignin based on deep eutectic solvent/cyclopentyl methyl ether system

A novel biphasic system containing water-soluble deep eutectic solvent (DES) and cyclopentyl methyl ether (CPME) was developed to treat Eucalyptus for furfural production, extracting lignin and enhancing cellulose enzymatic hydrolysis. Herein effect of DES type, water content in DES, temperature and time on furfural yield in water-soluble DES/CPME pretreatment process was firstly evaluated. A maximum furfural yield of 80.6 % was attained in 10 min at 150 °C with choline chloride (ChCl)/citric acid monohydrate (CAM)/CPME system containing 30 wt% water and 2.5 wt% SnCl4·5H2O, which was higher than that obtained from ChCl/CAM/CPME system without water (55.5 %) and H2O/CPME system (49.7 %). These results demonstrated that the water-soluble DES/CPME system was a powerful method enhancing the furfural production. Under the optimal pretreatment conditions, the delignification and glucose yield were reached to 72.7 % and 94.3 %, respectively. The extracted lignin showed low molecular weight and β-aryl-ether was obviously cleaved. Additionally, water-soluble DES/CPME pretreatment led to a significant removal of hemicelluloses (100.0 %) and lignin (72.7 %) and introduced morphological changes on cell walls, especially from the cell corner (CC) and secondary wall (SW) layers. Overall, this work proposed a practical one-step fractionation strategy for co-producing furfural, lignin and fermentable sugar, providing a way to biorefinery.

Establishment of efficient system for bagasse bargaining: Combining fractionation of saccharides, recycling of high-viscosity solvent and dismantling

Sugarcane bagasse (SCB) has a recalcitrant structure, which hinders its component dismantling and subsequent high value utilization. Some organic solvents are favorable to dismantle lignocellulose, but their high viscosity prevents separation of components and reuse of solvents. Herein, ethylene glycol phenyl ether (EGPE)-acid system is used as an example to develop green and efficient methods to dismantle SCB, purify polysaccharides and lignin, and reuse solvents. Results show that dismantling SCB at 130 °C, 0.5 % H2SO4, and 100 min can obtain 85.5 % cellulose recovery, 94.1 % hemicellulose removal and 83.7 % lignin removal. Different molecular weight saccharides are separated by membranes filtration and centrifugation, and lignin recovered by antisolvent precipitation. The solvent recovered by distillation, achieving high dismantling efficiency of 89.2 % cellulose recovery, 94.1 % hemicellulose removal and 94.4 % lignin removal after four recycles. Results show a promising approach for the closed-loop process of dismantling lignocellulose, fractionating saccharides, and reusing solvents in high-viscosity systems.

Simultaneous production of furfural, lignin and cellulose-rich residue from Eucalyptus urophylla × E. grandis by ChCl/1,2-propanediol/MIBK biphasic system pretreatment

A facile biphasic system composed of choline chloride (ChCl)-based deep eutectic solvent (DES) and methyl isobutyl ketone (MIBK) was developed to realize the furfural production, lignin separation and preparation of fermentable glucose from Eucalyptus in one-pot. Results showed that the ChCl/1,2-propanediol/MIBK system owned the best property to convert hemicelluloses into furfural. Under the optimal conditions (MRChCl:1,2-propanediol = 1:2, raw materials:DES:MIBK ratio = 1:4:8 g/g/mL, 0.075 mol/L AlCl3·6H2O, 140 °C, and 90 min), the furfural yield and glucose yield reached 65.0 and 92.2 %, respectively. Meanwhile, the lignin with low molecular weight (1250-1930 g/mol), low polydispersity (DM = 1.25-1.53) and high purity (only 0.08-2.59 % carbohydrate content) was regenerated from the biphasic system. With the increase of pretreatment temperature, the β-O-4, β-β and β-5 linkages in the regenerated lignin were gradually broken, and the content of phenolic hydroxyl groups increased, but the content of aliphatic hydroxyl groups decreased. This research provides a new strategy for the comprehensive utilization of lignocellulose in biorefinery process.

Fully upgrade bamboo biomass into three multifunctional products through biphasic γ-valerolactone and aqueous phosphoric acid pretreatment

In this manuscript, three components of lignocellulosic biomass were obtained by deconstructing bamboo with γ-valerolactone-H2O biphasic system, and the delignification rate of 80.92 % was achieved at 120 °C for 90 min. Lignin nanospheres with diameters ranging from 75 nm to 2 um could be customized by varying the self-assembly rate. Furthermore, the lignin nanospheres-poly(vinyl alcohol) film was prepared by cross-linking lignin nanospheres and poly(vinyl alcohol), which can obtain 90 % ultraviolet absorption capacity, while the light transmittance in non-ultraviolet band was almost unchanged. At the same time, due to the strong hydrogen formation between lignin nanospheres and poly(vinyl alcohol) bond network, the tensile properties of the composite film were also improved by 30 %. Besides, the high specific surface area of biomass-derived porous biochar (2056 m2/g) can be obtained after carbonization of solid residues at 850 °C for 2 h, which was almost 8 times the specific surface area of the direct biomass carbonization due to the removal of lignin and hemicellulose. biomass-derived porous biochar can be used as an adsorbent, with a CO2 capture capacity of 4.5 mmol g-1 at normal temperature (25 °C, 1 bar). The filtrate after the reaction contained a large amount of hemicellulose oligomers, which can be reacted with dichloromethane at 170 °C for 1 h to obtain the furfural yield of 74 %. In summary, the proposed biorefinery scheme achieves a full-component upgrade of lignocellulose and can be further applied in various downstream fields.

Fractionation of lignin from rice straw using an acidified biphasic solvent system

To obtain lignin from lignocellulosic biomass, phenoxyethanol (EPH) was employed to construct a biphasic solvent system. The concentration of EPH in this biphasic solvent system was first studied to determine a pretreatment condition for fractionation of lignin. Then, the fractionation of lignin from rice straw was performed under the conditions of temperature 130 °C, cooking time 60 min and sulfuric acid concentration 0.1 M, in 70 % aqueous EPH solvent system. The results showed that 50.97 %, 49.52 % or 82.02 % of the removed lignin with the purity of 89.04 %, 91.30 % or 84.76 % was regenerated from EPH liquor using dimethyl carbonate (DMC), dimethoxymethane (DMM) or diethyl ether (DE) as precipitant, respectively. Additionally, the weight-average molecular weight (Mw) and dispersity index (Đ) of the regenerated lignin decreased to 4247-4809 g/mol and 1.26-1.60 compared with that of the original lignin (5654 g/mol and 4.78). Finally, the compositional and structural characteristics of lignin, e.g., molecular weight and molecular structure, were also investigated by DSC, HSQC and elemental analysis.

Microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system for one-pot fractionation and valorization of Eucalyptus biomass

The developing of pretreatment method to break the biomass barrier of lignocellulosic is a challenging task for achieve high value utilization. A fast microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system was constructed for pretreating Eucalyptus to the production of furfural and cellulose-rich residues and the extraction of lignin. Results showed that the combination of AlCl₃·6H₂O and HCl had the best catalytic ability for furfural production among the examined catalysts. Under the optimal conditions (140 °C, 15 min, 0.075 M AlCl₃·6H₂O, 0.05 M HCl), the furfural yield of 55.4 %, the glucose yield of 90.3 % and the delignification rate of 92.4 % could be achieved. Moreover, the extracted lignin samples with a low polydispersity (1.55-1.73) and molecular weight (1380-2040 g/mol) are promising to act as precursor for the value-add products processing. These findings demonstrated an ultrafast pretreatment process with excellent results in biomass fractionation and comprehensive utilization of biomass components.

Biphasic fractionation of lignocellulosic biomass based on the combined action of pretreatment severity and solvent effects on delignification

A novel method based on pretreatment severity and solvent effects on delignification, was introduced to pretreat and fractionate lignocellulose in a 2-phenoxyethanol (EPH) biphasic solvent system. The combined severity factor (CSF) was used to regulate pretreatment severity, and the relative energy difference (RED) of solvent system to lignin was used to evaluate solvent effects. The combined action of pretreatment severity and solvent effects on delignification was first investigated by the response surface regression analysis on the pretreatment of Amorpha. Accordingly, pretreatment and fractionation of Amorpha, poplar and corn straw were then conducted under the optimized conditions. Results showed that >99 % lignin was removed after pretreatment with CSF 3.7845 in a solvent system with RED 0.9371, and 42.94 %, 39.41 % and 70.90 % lignin from Amorpha, poplar and corn straw were respectively regenerated from organosolv liquor after fractionation. Finally, the regenerated products were characterized by FTIR, TG and GPC analysis.

Recent progress in direct production of furfural from lignocellulosic residues and hemicellulose

Furfural is a vital biomass-derived platform molecule, which can be used to synthesize a wide range of value-added chemicals. Furfural and its derivatives are promising alternatives to conventional petroleum chemicals. However, recent industrial production of furfural existed some thorny problems, including low efficiency, energy waste, and environmental pollution. Therefore, tremendous and continuous efforts have been made by researchers to develop novel furfural production processes with high economic viability, production efficiency, and sustainability. This review summarized the merits and shortcomings of disparate catalytic systems for the synthesis of furfural from biomass and biomass pretreatment hydrolysate on the basis of recently published literature. Furthermore, the suggestions for furfural production research were put forward.

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.

Hydrothermal pretreatment of lignocellulosic biomass for hemicellulose recovery

The hemicellulosic fraction recovery is of interest for integrated processes in biorefineries, considering the possibility of high economic value products produced from their structural compounds of this polysaccharide. However, to perform an efficient recovery, it is necessary to use biomass fractionation techniques, and hydrothermal pretreatment is highlighted as a valuable technique in the hemicellulose recovery by applying high temperatures and pressure, causing dissolution of the structure. Considering the possibility of this pretreatment technique for current approaches to hemicellulose recovery, this article aimed to explore the relevance of hydrothermal pretreatment techniques (sub and supercritical water) as a strategy for recovering the hemicellulosic fraction from lignocellulosic biomass. Discussions about potential products to be generated, current market profile, and perspectives and challenges of applying the technique are also addressed.

Charge-oriented strategies of tunable substrate affinity based on cellulase and biomass for improving in situ saccharification: A review

The intrinsic recalcitrance of lignocellulosic biomass makes it resistant to enzymatic hydrolysis. The electron-rich surface of the lignin and cellulose-alike structure of hemicellulose competitively absorb the cellulase. Thus, modifying the surface charge on biomass components to alter cellulase affinity is an urgent requisite. Developing charge tunable cellulase will alter substrate affinity. Also, charge-based immobilization generates controllable substrate affinity. Within immobilized cellulase involved in situ biomass saccharification, charge effects made a crucial contribution. In addition to affecting the interaction between immobilized cellulase and biomass, charge exerts an impact on cellulase to immobilize the materials, further investigation is essential. This study aims to review the charge effects on the cellulase affinity in biomass saccharification, strategies of charge tunable cellulase, and immobilized cellulase, thereby explaining the role of electrostatic interaction. In terms of electrostatic behavior, the pathways and plans to improve in situ biomass saccharification seem to be promising.

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.

One-pot selective conversion of lignocellulosic biomass into furfural and co-products using aqueous choline chloride/methyl isobutyl ketone biphasic solvent system

This study investigated simultaneous lignocellulose fractionation and conversion in a one-pot reaction using an aqueous choline chloride/methyl isobutyl ketone (ChCl/MIBK) biphasic solvent system. Under the optimized condition (170 °C, 60 min, 0.6 wt% H₂SO₄, 10.7 wt% solid loading), the biphasic solvent solubilized 96% xylan in raw switchgrass, which was simultaneously converted to furfural with a yield of 84.04%. The biphasic solvent was also able to selectively extract lignin, which had a high purity (93.1%), and uncondensed moieties (i.e., Hibbert's ketone), as well as decreased molecular weight and polydispersity index. The resultant pulp was enriched with cellulose (73.3%), which can be completely hydrolyzed into glucose within 48 h via enzymatic hydrolysis. Aqueous ChCl was successfully recycled and reused for atleast three cycles with similar performance in switchgrass fractionation. This study demonstrated that aqueous ChCl/MIBK biphasic system was an effective solvent system for co-production of furfural, high quality technical lignin and digestible cellulose for further upgrading.

Lewis acid-catalyzed biphasic 2-methyltetrahydrofuran/H2O pretreatment of lignocelluloses to enhance cellulose enzymatic hydrolysis and lignin valorization

Lewis acid-catalyzed pretreatment in a biphasic system consisting of bio-based solvent 2-methyltetrahydrofuran (2-MeTHF) and water for a highly integrated one-pot catalytic transformation of lignocelluloses have been achieved. The aim of this work was to study the effects of different Lewis acid catalysts and pretreatment temperatures on the structural characteristics of precipitated lignin and enzymatic hydrolysis of the pretreated substrates, as well as the quantitative analysis of precipitates, solid residues, soluble carbohydrates and inhibitors. After the AlCl₃-catalyzed biphasic 2-MeTHF/H₂O pretreatment at 180 °C, its maximum cellulose conversion rate was enhanced by 7.4-fold as compared to the raw material. The precipitated lignin exhibited the representative structure, relatively low molecular weight and high purity for preparing value-added aromatic chemicals or renewable polymers. Overall, AlCl₃-catalyzed biphasic 2-MeTHF/H₂O pretreatment may offer a promising approach for enhancing enzymatic hydrolysis and obtaining valorized lignin by-product.

One-pot co-catalysis of corncob with dilute hydrochloric acid and tin-based solid acid for the enhancement of furfural production

A newly synthesized solid acid catalyst SO₄^2-/SnO₂-diatomite was prepared for synthesizing furfural from corncob in the presence of homogeneous Brönsted acid. The relationship between pKa of Brönsted acid and turnover frequency (TOF) of co-catalysis with Brönsted acid plus SO₄^2-/SnO₂-diatomite was explored on the conversion of corncob to furfural. HCl (pKa = -7.0) (0.5 wt%) plus SO₄^2-/SnO₂-diatomite (3.6 wt%) gave the highest furfural yield (40.1%) with TOF value at 2.98 h^-1 in the aqueous media. In the γ-valerolactone-water (6:4, v:v) biphasic media containing 15 g/L ZnCl₂, one-pot conversion of corncob with co-catalysts gave a furfural yield of 68.9% at 170 °C for 30 min. Additionally, an efficient SO₄^2-/SnO₂-diatomite recycling was achieved with a productivity of 15.6 g furfural/(g solid acid·day) after 5 cycles of repeated use. Clearly, this one-pot co-catalysis process has high potential application for furfural production in future.

Camellia oleifera shell as an alternative feedstock for furfural production using a high surface acidity solid acid catalyst

This paper focuses on the high-value transformation of camellia oleifera shell, which is an agricultural waste enriched in hemicellulose. An efficient catalytic route employing sulfonated swelling mesoporous polydivinylbenzene (PDVB-SO₃H) as catalyst in monophasic or biphasic solvents was developed for the conversion of raw camellia oleifera shell into furfural. The reaction parameters were evaluated and optimized for improving the furfural yield. It was found that the solvent greatly influenced the hydrolysis of camellia oleifera shells, and the highest furfural yield of 61.3% was obtained in "γ-butyrolactone + water" system when the feedstock-to-catalyst ratio was 2 for 30 min at 443 K. Camellia oleifera shell exhibited a high potential as feedstock to produce furfural in high yields. The outcome of this study provides an attractive utilization option to camellia oleifera shell, which is currently burned or discarded for producing a bio-based chemical.

Chemical-enzymatic conversion of corncob-derived xylose to furfuralcohol by the tandem catalysis with SO42-/SnO2-kaoline and E. coli CCZU-T15 cells in toluene-water media

One-pot synthesis of furfuralcohol from corncob-derived xylose was attempted by the tandem catalysis with solid acid SO₄^2-/SnO₂-kaoline and recombination Escherichia coli CCZU-T15 whole-cells in the toluene-water media. Using SO₄^2-/SnO₂-kaoline (3.5wt%) as catalyst, the furfural yield of 74.3% was obtained from corncob-derived xylose in the toluene-water (1:2, v:v) containing 10mM OP-10 at 170°C for 30min. After furfural liquor was mixed with corncob-hydrolysate from the enzymatic hydrolysis of oxalic acid-pretreated corncob residue, furfural (50.5mM) could be completely biotransformed to furfuralcohol with Escherichia coli CCZU-T15 whole-cells harboring an NADH-dependent reductase (ClCR) in the toluene-water (1:3, v:v) containing 12.5mM OP-10 and 1.6mM glucose/mM furfural at 30°C and pH 6.5. Furfuralcohol was obtained at 13.0% yield based on starting material corncob (100% furfuralcohol yield for bioreduction of furfural step). Clearly, this one-pot synthesis of furfuralcohol strategy shows high potential application for the effective utilization of corncob.