Using a combined hydrolysis factor to balance enzymatic saccharification and the structural characteristics of lignin during pretreatment of Hybrid poplar with a fully recyclable solid acid

Valorization of Lignocellulose with One-Step Acidified Monophasic Phenoxyethanol Fractionation

Effective fractionation of lignocelluosic biomass and subsequent valorization of all three major components under mild conditions were achieved. Pretreatment with acidified monophasic phenoxyethanol (EPH) efficiently removed 92.6 % lignin and 80 % xylan from poplar at 110 °C in 60 min, yielding high-value EPH-xyloside, EPH-modified lignin (EPHL), and a solid residue nearly purely composed of carbohydrates. After removing the grafted acetyl groups using 1 % NaOH at 50 °C, the highest enzymatic digestibility reached 92.3 %. EPHL could be recovered in high yield and purity with an uncondensed structure, while xylose was converted to EPH-xyloside, a potential precursor in biomedical industries. Additionally, the acidified monophasic EPH solvent could effectively fractionate biomass from species other than hardwood, achieving over 70 % delignification from recalcitrant pinewood under the same mild conditions, demonstrating the high potential of monophasic EPH pretreatment.

Preparation of Alkali-Resistant Lignin Nanospheres Loaded with Silver Nanoparticles and Their Applications Toward Antibiosis and Printing

Lignin nanoparticles (LNPs) loaded with silver nanoparticles have exhibited significant application potential in antibacterial and catalytic fields. However, the high solubility of LNPs in silver ammonia solution makes it difficult to achieve the reduction of Ag+ and the adsorption of silver nanoparticles. In this study, a protecting agent, terephthalic aldehyde (TA) is used to block lignin condensation and introduce aldehyde groups onto the lignin molecular backbone during lignin extraction. Furthermore, the TA stabilized lignin (TASL) is cross-linked with bisphenol A diglycidyl ether (BADGE) to enhance its alkali resistance performance and subsequently prepared into alkali-resistance BADGE- TASL hybrid LNPs (BADGE- TASL hy-LNPs) by anti-solvent precipitation and self-assembly. Because the presence of a large number of aldehyde groups in TASL compensates for the loss of phenolic hydroxyl groups caused by crosslinking reactions, a high loading of silver nanoparticles of 54.00% is obtained after redox reaction and adsorption in silver ammonia solution. When the BADGE-TASL hy-LNPs@Ag is used as an antibacterial agent, its inhibition efficiency reached ≈99%. Besides, the BADGE-TASL hy-LNPs@Ag can serve as a printing material for the preparation of conductive printing ink. Therefore, this study provides a strategy for lignin functionalization and application in printed electronics and antimicrobial fields.

Lignocellulosic biomass pretreatment with a lignin stabilization strategy and valorization toward multipurpose fractionation

Lignocellulosic biomass has emerged as a promising alternative with sustainable advantages for the production of a wide range of renewable products and value-added chemicals. In this study, a pretreatment strategy that use a fully recyclable acid hydrotrope (p-TsOH aqueous solution) to extract lignin and employ glyoxylic acid (GA) to stabilize lignin was proposed for biomass valorization toward multipurpose fractionation. 83.0 % of lignin was dissolved out by p-TsOH hydrotrope (80 wt%) with GA addition to form GA-stabilized product at 80 o C for 15 min. The stabilized lignin was subsequently used as an additive in the preparation of lignin-based suncream. Notably, the incorporation of 4 wt% lignin nanospheres into an SPF15 sunscreen yielded a measured SPF of 59.94. Furthermore, the depolymerization of uncondensed lignin into aromatic monomers yielded a high lignin-oil yield of 84.2 %. Additionally, direct heating of the pretreatment liquor facilitated the conversion of monosaccharides into furfural, achieving a desired yield of 53.7 % without the addition of any acid catalyst. The pretreatment also enhanced the enzymatic hydrolysis of glucan, resulting in a saccharification yield of 98.4 %. Moreover, short-term ultrasonication of the pretreated substrate yielded pulp suitable for papermaking. Incorporating 15 wt% fibers into the produced paper sheets led to a 5.3 % increase in tear index and a 25.4 % increase in tensile index. This study presents a viable pretreatment strategy for the multipurpose fractionation of lignocellulosic biomass, offering potential avenues for biomass valorization.

Natural arginine-based deep eutectic solvents for rapid microwave-assisted pretreatment on crystalline bamboo cellulose with boosting enzymatic conversion performance

Development of amino acid-based natural deep eutectic solvents (DESs) pretreatment technology on lignocellulosic biomass is a promising approach to biorefinery. In this study, for arginine-based DESs with different molar ratios, the viscosity and Kamlet-Taft solvation parameters were quantified to evaluate the pretreatment performance on bamboo biomass. Further, microwave assisted DES pretreatment was eminent, evidenced by 84.8% lignin removal and increased saccharification yield (from 6.3% to 81.9%) in moso bamboo at 120 °C and ratio of 1:7 (arginine: lactic acid). Results showed degradation of lignin molecules together with release of phenolic hydroxyl units after DESs pretreatment, which is conducive to subsequent utilization. Meanwhile, DES-pretreated cellulose exhibited unique structural characteristics including destroyed crystalline region of cellulose (Crystallinity Index from 67.2% to 53.0%), decreased crystallite size (from 3.41 nm to 3.14 nm) and roughened fiber surface. Thus, arginine-based DES pretreatment has excellent potential in bamboo lignocellulose pretreatment.

Simultaneous achievement of efficient hemicellulose separation and inhibition of lignin repolymerization using pyruvic acid treatment

The efficiency of organic acid treatment in the conversion of lignocellulosic biomass fractions has been widely recognized. In this study, a novel green pyruvic acid (PA) treatment is proposed. The higher separation efficiency of eucalyptus hemicellulose was obtained at 4.0% PA and 150 °C. The hemicellulose separation yield was increased from 71.71 to 88.09% compared to glycolic acid (GA) treatment. In addition, the treatment time was significantly reduced from 180 to 40 min. The proportion of cellulose in the solid increased after PA treatment. However, the accompanying separation of lignin was not effectively controlled. Fortunately, a six-membered ring structure was formed on the diol structure of the lignin β-O-4 side chain. Fewer lignin-condensed structures were observed. High-value lignin rich in phenol hydroxyl groups were obtained. It provides a green path for the simultaneous achievement of efficient hemicellulose separation and inhibition of lignin repolymerization using organic acid treatment.

Valorization of Boehmeria nivea stalk towards multipurpose fractionation: furfural, pulp, and phenolic monomers

BACKGROUND

As one of the most abundant bioresource in nature, the value-added utilization of lignocellulosic biomass is limited due to its inherent stubbornness. Pretreatment is a necessary step to break down the recalcitrance of cell walls and achieve an efficient separation of three main components (cellulose, hemicelluloses, and lignin).

RESULTS

In this study, hemicelluloses and lignin in Boehmeria nivea stalks were selectively extracted with a recyclable acid hydrotrope, an aqueous solution of P-toluenesulfonic acid (p-TsOH). 79.86% of hemicelluloses and 90.24% of lignin were removed under a mild pretreatment condition, C80T80t20, (acid concentration of 80 wt%, pretreatment temperature and time of 80 °C and 20 min, respectively). After ultrasonic treatment for 10 s, the residual cellulose-rich solid was directly converted into pulp. Subsequently, the latter was utilized to produce paper via mixing with softwood pulp. The prepared handsheets with a pulp addition of 15 wt% displayed higher tear strength (8.31 mN m2/g) and tensile strength (8.03 Nm/g) than that of pure softwood pulp. What's more, the hydrolysates of hemicelluloses and the extracted lignin were transformed to furfural and phenolic monomers with yields of 54.67% and 65.3%, respectively.

CONCLUSIONS

The lignocellulosic biomass, Boehmeria nivea stalks, were valorized to pulp, furfural, and phenolic monomers, successfully. And a potential solution of comprehensive utilization of Boehmeria nivea stalks was provided in this paper.

Effect of Fenton oxidized lignin support on immobilized β-glucosidase activity

In this study, the Fenton oxidized lignin was prepared to investigate the effect of Fenton oxidation modification on the activity of lignin immobilized β-glucosidase (β-GL). The results demonstrated that Fenton oxidation could significantly improve the activity and stability of immobilized β-GL. This is because the Fenton oxidation increased the electrostatic, hydrogen bonding, and hydrophobic forces between lignin and β-GL, resulting in increased lignin adsorption onto β-GL. The Fenton oxidation also changed the chemical structure of lignin, altering the lignin-β-GL binding site and reducing the negative effect of lignin on the β-GL catalytic domain. This research will improve understanding of the effect of Fenton lignin oxidation on immobilized β-GL activity and expand the use of lignin in enzyme immobilization.

A cascade valorization of Kenaf stalk for the preparation of lignin sunscreens and papermaking

Lignin has been regarded as a potential natural sun screening agent. However, the dark color of traditional industrial lignin hinders its application in the field of skincare. In this study, a green and facile approach was developed to extract light-colored lignin. p-Toluenesulfonic acid (p-TsOH) was used to separate lignin and fibers from Kenaf stalks. During the isolation of lignin, formaldehyde was added to preserve the β-O-4 bonds of lignins in the form of stable acetals. The obtained lignin was further employed to prepare nanoparticles (LNPs) as sunscreen additives. After adding 4 wt% LNPs, the SPF values of the cream increased from 7.05 to 27.84. The residual fibers from the Kenaf stalks can be utilized for papermaking as the raw materials. by mixing them with softwood pulp to reduce the consumption of commercial pulp. With the addition of 5 wt% residual fibers in commercial softwood pulp, the produced paper showed better mechanical properties. The ring crush strength index and tear index of the samples increased from 2.49 N·m/g and 4.63 mN·m²/g to 2.62 N·m/g and 4.75 mN·m²/g, respectively. This study paved a way for the comprehensive utilization of Kenaf stalks towards not only papermaking but also daily chemical products.

A hydrotrope pretreatment for stabilized lignin extraction and high titer ethanol production

The biomass pretreatment strategies using organic acids facilitate lignin removal and enhance the enzymatic digestion of cellulose. However, lignin always suffers a severe and irreversible condensation. The newly generated C-C bonds dramatically affect its further upgrading. In this study, we used a recyclable hydrotrope (p-Toluenessulfonic acid, p-TsOH) to dissolve lignin under mild condition and stabilized lignin with a quenching agent (formaldehyde, FA) during extraction, achieving both value-added lignin extraction and efficient enzymatic saccharification of cellulose. Approximately 63.7% of lignin was dissolved by 80% (wt. %) p-TsOH with 1.5% FA addition at 80 °C, 30 min. The obtained lignin was characterized by FTIR spectroscopy, TGA, 2D HSQC NMR spectroscopy, and GPC. The results indicated that the extracted lignin exhibited excellent properties, such as light color, a low molecular weight (Mw, 5371 g/mol), and a narrow polydispersity (Mw/Mn, 1.63). The pretreated substrate was converted to ethanol via a quasi-simultaneous saccharification and fermentation process (Q-SSF). After fermentation of 60 h, the ethanol concentration reached 38.7 ± 3.3 g/L which was equivalent to a theoretical ethanol yield of 82.9 ± 2.2% based on the glucan content, while the residual glucose concentration was only 4.69 ± 1.4 g/L. In short, this pretreatment strategy protected lignin to form new C-C linkages and improved the enzymatic saccharification of glucan for high-titer ethanol production.

Insights into alkaline choline chloride-based deep eutectic solvents pretreatment for Populus deltoides: Lignin structural features and modification mechanism

Deep eutectic solvent (DES) is a kind of green solvent for biorefinery, which favors the progress of being more environmentally friendly and effective. A better understanding of structural changes of lignin is necessary to optimize pretreatment conditions and efficient utilization of the resultant lignin. The current study reported the structural features of lignin recovered from alkaline ChCl/imidazole and ChCl/urea DES pretreatment, and the mechanism of lignin modification was revealed. The profiling demonstrated that lignin samples possessed a high purity (>94.4%), low molecular weight ranging from 1544 to 2562 g/mol and an excellent uniformity (PDI < 1.6). Noteworthy, the content of β-O-4' linkages in lignin was over 75% (i.e. 72.2%-77.4% retention); S/G ratio was increased whereas the content of -OCH₃ groups were decreased. It was revealed that slight cleavage of β-O-4' linkages, preferential breakdown of G units, and demethylation reaction were occurred during alkaline ChCl-based DES pretreatment. Specifically, cleavage of ester linkages between PB and lignin macromolecule was taking place during ChCl/imidazole pretreatment at a high temperature; whereas oxidation only appeared in ChCl/urea system. Despite the modification, well β-O-4' preserved and less condensed lignin samples were recovered after low-temperature pretreatment. Consequently, high contents of phenol derivatives (26.3-30.6%) were achieved in lignin oil. The present study provides critical information on alkaline ChCl-based DES pretreatment, which will contribute to the valorization of lignin by-products and will be beneficial to the development of biorefineries.

Thread Rolling: An Efficient Mechanical Pretreatment for Corn Stover Saccharification

Sugar cane bagasse and corn stalks are rich in lignocellulose, which can be degraded into monosaccharides through enzymatic hydrolysis. Appropriate pretreatment methods can effectively improve the efficiency of lignocellulose enzymatic hydrolysis. To enhance the efficiency of enzymatic hydrolysis, thread rolling pretreatment as a physical pretreatment was applied in this study. The influence of raw material meshes size after pretreatment was also taken as the research target. Specific surface area analysis, Scanning electron microscope (SEM), X-rays diffraction (XRD), and Fourier transform infrared (FT-IR) were used for characterizations. The results showed that, the total monosaccharide recovery rates of the raw materials, 20–40 mesh, 40–60 mesh, and 60–80 mesh enzymolysis substrates were 17.6%, 34.58%, 37.94%, and 50.69%, respectively. The sample after pretreatment showed a better recovery of monosaccharide than that of the raw material. Moreover, the enzymolysis substrates with a larger mesh exhibited a higher recovery of monosaccharide than that of the enzymolysis substrates with smaller meshes. This indicated that thread rolling pretreatment can effectively improve the efficiency of enzymatic hydrolysis.

Impact of centrifugation treatment on enzymatic hydrolysis of cellulose and xylan in poplar fibers with high lignin content

Centrifugation is very common in the production and treatment of lignocellulose for applications like pretreatment for enzymatic hydrolysis, but it is not certain whether it affects applications of lignocellulose and almost no one realizes this problem. This study investigated the effects of centrifugation on the characteristics and enzymatic hydrolysis of poplar fibers with high lignin content. The results showed that centrifugation inhibited the enzymatic hydrolysis of fiber, but fiber characteristics and enzymatic digestibility fluctuated with increasing centrifugation time. Centrifugation for about 15 min had the least effect on fiber properties while centrifugation for 30 min had the least effect on enzymatic hydrolysis. The water retention value was closely related to the enzymatic digestibility, but the pore characteristics and crystallinity index could not reflect the enzymatic accessibility of the fiber. This article will provide useful references for the enzymatic hydrolysis of lignocellulose and other high-value applications to improve production efficiency furtherly.

Comparison of enzymatic saccharification and lignin structure of masson pine and poplar pretreated by p-Toluenesulfonic acid

p-Toluenesulfonic acid (p-TsOH) with the hydrotropic and recyclable properties is widely used for rapid remove of lignin from lignocelluloses at low temperature (<100 °C). In this work, both softwood masson pine and hardwood poplar were pretreated with p-TsOH under different conditions and then subjected to enzymatic hydrolysis to compare the effect of p-TsOH pretreatment on their saccharification and lignin structure. Results showed p-TsOH has sensitive selectivity to lignin structure during pretreatment. Around 95% of lignin in poplar can be dissolved at 80 °C within 30 min, while for masson pine, the delignification is only 50%. Following enzymatic hydrolysis with cellulase loading of 20 FPU/g-cellulose for 72 h, the highest sugar yield of pretreated poplar and masson pine is 92.13% and 29.46%, respectively, which indicates that p-TsOH pretreatment alone works well with hardwoods (poplar). Structural analysis of removed lignin implies that p-TsOH mainly results in the cleavage of β-aryl ether bonds of lignin side chains, and the aromatic structure of lignin keeps intact. p-TsOH pretreatment shows the key advantages of low cost and rapid delignification for highly enzymatic saccharification, and provides a promising and green pathway for the development of low cost and sustainable bio-based products for developing a bio-based economy.

Sustainability metrics of pretreatment processes in a waste derived lignocellulosic biomass biorefinery

Excessive utilization of fossil fuels has resulted in serious concerns about climate change. Integrating biorefinery technology to convert waste-derived-lignocellulosic biomass into biofuels and biopolymers has become an emerging topic toward our sustainable future. Pretreatment to fractionate the building block chemicals from the biomass is a crucial unit operation to ease the downstream processes in biorefinery. However, application of solvents and chemicals in the process can create many operational and environmental challenges in sensitive areas like highly populated cities. To shed light on how to determine a green biorefinery, this study presents the sustainability metrics of various pretreatment techniques and their operational risks during urbanization. The proposed green indexes include fractionation outputs, chemical recyclability, operational profile, and safety factors. In line with the design principles of lignin valorization, the issue of urban biomass and water-and-energy nexus are addressed to support future development and application of urban biorefinery for municipal waste management.

Valorization of Alkaline Peroxide Mechanical Pulp by Metal Chloride-Assisted Hydrotropic Pretreatment for Enzymatic Saccharification and Cellulose Nanofibrillation

Developing economical and sustainable fractionation technology of lignocellulose cell walls is the key to reaping the full benefits of lignocellulosic biomass. This study evaluated the potential of metal chloride-assisted p-toluenesulfonic acid (p-TsOH) hydrolysis at low temperatures and under acid concentration for the co-production of sugars and lignocellulosic nanofibrils (LCNF). The results indicated that three metal chlorides obviously facilitated lignin solubilization, thereby enhancing the enzymatic hydrolysis efficiency and subsequent cellulose nanofibrillation. The CuCl₂-assisted hydrotropic pretreatment was most suitable for delignification, resulting in a relatively higher enzymatic hydrolysis efficiency of 53.2%. It was observed that the higher residual lignin absorbed on the fiber surface, which exerted inhibitory effects on the enzymatic hydrolysis, while the lower lignin content substrates resulted in less entangled LCNF with thinner diameters. The metal chloride-assisted rapid and low-temperature fractionation process has a significant potential in achieving the energy-efficient and cost-effective valorization of lignocellulosic biomass.

Improving cellulose nanofibrillation of waste wheat straw using the combined methods of prewashing, p-toluenesulfonic acid hydrolysis, disk grinding, and endoglucanase post-treatment

Here we established a new approach for improving the cellulose nanofibrillation of high ash content waste wheat straw (WWS). The results were comprehensively elucidated from the ash removal, delignification, mechanical fibrillation and endoglucanase post-treatment. When water dosage was increased from 50 to 500 times of the WWS weight, the ash content gradually decreased during prewashing process, which facilitated lignin solubilization in subsequent p-toluenesulfonic acid (p-TsOH) hydrolysis. Approximately 80% of lignin in prewashed WWS could be dissolved during acid hydrolysis to result in a relatively higher crystallinity of 59.1%. Compared with the lignocellulosic nanofibrils (LCNF) directly obtained using acid hydrolysis and disk grinding, prewashing-assisted acid hydrolyzed WWS was fibrillated into LCNF with smaller height of 57.0 nm. Mild endoglucanase post-treatment could further produce less entangled LCNF with thinner diameters. In short, this study presented a promising and green pathway to achieve an efficient utilization of agricultural residue wastes to cellulose nanomaterials.