Comparison of the Degradation Performance of Seven Different Choline Chloride-Based DES Systems on Alkaline Lignin

Valorization of wheat straw through enhancement of cellulose accessibility, xylan elimination and lignin removal by choline chloride:p-toluenesulfonic acid pretreatment

Different molar ratio of choline chloride (ChCl) and p-toluenesulfonic acid (p-TsOH) (2:1, 1:1 and 1:2, mol:mol) were used to prepare deep eutectic solvents (ChCl:p-TsOH) for pretreating cellulose fibers to elevate cellulose accessibility, enhance xylan elimination, increase lignin removal and promote enzymatic digestion. ChCl:p-TsOH (1:1, mol:mol) could effectually destroy the dense layout of wheat straw (WS) at 80 °C for 60 min. Cellulose crystallinity declined from 43.4 % to 25.5 %, and the lignin surface area and hydrophobicity were reduced to 182.6 m2/g and 3.2 L/g, respectively. While cellulose accessibility in WS was significantly improved to 523.9 mg/g. The delignification and xylan removal reached 72.4 % and 90.5 %, respectively. The enzymatic digestibility reached 89.3 %. Furthermore, molecular dynamics simulation and quantum chemistry calculation were conducted on the lignocellulose model. The van der Waals interaction between ChCl:p-TsOH and lignin and the dispersion interaction between ChCl and lignin were identified. Accordingly, the interaction between biomass and ChCl:p-TsOH was elucidated at the molecular level. It provided a comprehensive understanding of lignocellulosic biomass valorization through the highly efficient pretreatment by ChCl:p-TsOH.

Effective extraction of larch holocellulose with alkaline deep eutectic solvent and production of furan chemicals with the coordination of temperature-controlled polyoxometalates and metal salt in biphasic system

This study focused on extracting holocellulose from Changbai larch waste, which is rich in hexose and beneficial for furan chemicals production. Various alkaline deep eutectic solvents (DESs) was applied in the extraction of holocellulose. DES composed of lysine (Lys) and 2-aminoethanol (MEA) with strong alkalinity had a superior ability to remove lignin, and the purity of holocellulose could reach 82.7 %. Consequently, a double-acid system formed by a temperature-controlled polyoxometalates catalyst (ChnH3-nPW12, n = 1, 2, 3,) prepared by choline chloride (ChCl) and phosphotungstic acid (H3PW12O40) and different metal salts were used in the hydrolysis of holocellulose to 5-hydroxymethylfurfural (HMF) and 2-furaldehyde (FF) in a two-phase system of water and organic solvent. The yields of HMF and FF reached 43.5 % and 78.2 %, respectively, when ChH2PW12 and AlCl3 were employed under the conditions of 10 mL water/methyl isobutyl ketone (MIBK) (1:9, V:V), 9 h, and 150 °C. ChH2PW12is easy to recycle and can be used up to 5 times. This study offers a novel strategy to retain as much hemicellulose as possible to achieve holocellulose by alkaline DESs, and the one-pot process by the coordination of polyoxometalates and metal salt provides a simultaneous production of high-value furan chemicals from larch waste.

Acetylated lignin sulfonate as a biodegradable coating for controlled-release urea fertilizer: A novel acetylation method and diffusion coefficient analysis

Plants require essential nutrients to grow, which soil alone cannot provide. Chemical fertilizers like urea supply the necessary nutrients, including nitrogen. They quickly dissolve in water and can contaminate it with nitrate and nitrite, which can cause diseases. Slow-release fertilizers are a better option to reduce environmental risks. Researchers are exploring cheap and biodegradable alternatives, such as lignin. A critical discussion in the coated urea fertilizer is modeling the nitrogen diffusion process in the coating, which predicts the system's behavior. This article uses lignin sulfonate to coat urea fertilizer, which should first be acetylated with decanoyl chloride. One of the critical parameters is the diffusion coefficient (D). D is determined using the mass transfer flux and the completion time of the effective substance, and with its help, the graph of the total mass transferred from the membrane in a specific time (Mt) is determined. D equals 6.298813 × 10-8 cm2/s using the time lag method. Also, with the fixed-point convergence method, 5.8849 × 10-8 cm2/s was obtained, which has about 0.80 % error with the D obtained by the time lag method. The Mt obtained from the analytical method and the experimental data coincides with a minimal error, which indicates high accuracy.

One pot green process for facile fractionation of sorghum biomass to lignin, cellulose and hemicellulose nanoparticles using deep eutectic solvent

Complete valorization of lignocellulosic biomass is crucial for bio-based biorefineries to fulfil the circular bioeconomy concept. However, the existence of lignin carbohydrate complexes (LCC) in biomass hinders the simultaneous fractionation of biomass components, such as lignin, hemicellulose and cellulose, for subsequent biorefining processes. This study explores for the first time a novel approach tailored for the deconstruction of sorghum biomass components through efficient breakdown of LCC. Selective targeting of the major LCC linkages binding xylan and lignin was performed using an ultrasound-assisted deep eutectic solvent under mild treatment conditions. This process yielded a maximum cellulose content of 98.3 %, hemicellulose content of 95.2 %, and lignin content of 94.6 %, with the highest purities of 99.43 %, 96.71 %, and 98.12 %, respectively. FTIR, 2D-HSQC NMR and XRD analyses confirmed that most of the structural properties of lignin, hemicellulose, cellulose are retained. The lignocellulosic components were successfully valorised to cellulose, hemicellulose, and lignin nanoparticles with mean sizes of 64.5 ± 6 nm, 72.8 ± 4 nm and 57.2 ± 8 nm respectively, with good thermal stability. The proposed green process enables the complete utilization of agro-residue feedstock for the preparation of biomass-derived nanoparticles, thereby accelerating the economic and industrial prospects of bio-based biorefineries.

Characterization and properties of phenolic resin doped modified lignin

Phenolic resins occupy an important position in industrial applications, but phenol, one of the raw materials for synthesis, is a non-renewable resource. Lignin, as a natural polymer containing phenolic hydroxyl groups, alcohol hydroxyl groups and other reactive groups, can replace some of the phenol in the synthesis of phenolic resins, which can reduce the amount of phenol, thus reducing the cost of phenolic resins, while effectively promoting the high value-added use of renewable biomass resources. Due to its low reactivity, alkaline lignin is usually discharged as production waste, unaware that lignin macromolecules can be modified. In this paper, the phenolic monomers were obtained by acid-catalyzed depolymerization of DES (choline chloride/p-toluenesulfonic acid or choline chloride/lactic acid) from waste alkaline lignin, and the recovery rate of the DES solution during the catalytic treatment was more than 85 %, in which the main monomer was 2-methoxy-4-(1-propyl) phenol. The degradation of alkaline lignin is still favorable after five times of DES solvent recovery. The depolymerized lignin monomer replaced phenol by 50 wt% and then ternary co-polymerized with phenol and formaldehyde to form a biomass phenol-based phenolic resin, providing a green route for phenolic resin production. The cost of resin preparation was economically calculated, and it was found that the cost of resin after accumulating 4 cycles of DES treatment was only 51.1 % of that of pure phenolic resin. The density functional theory (DFT) was used to simulate the possible radical reactions in the intermediate process of phenolic resin reaction, to explore the microscopic mechanism and competition, to provide theoretical reference for further experimental realization of resin structure control and optimization, and to improve the theoretical system of resin synthesis.

Composition of Lignocellulose Hydrolysate in Different Biorefinery Strategies: Nutrients and Inhibitors

The hydrolysis and biotransformation of lignocellulose, i.e., biorefinery, can provide human beings with biofuels, bio-based chemicals, and materials, and is an important technology to solve the fossil energy crisis and promote global sustainable development. Biorefinery involves steps such as pretreatment, saccharification, and fermentation, and researchers have developed a variety of biorefinery strategies to optimize the process and reduce process costs in recent years. Lignocellulosic hydrolysates are platforms that connect the saccharification process and downstream fermentation. The hydrolysate composition is closely related to biomass raw materials, the pretreatment process, and the choice of biorefining strategies, and provides not only nutrients but also possible inhibitors for downstream fermentation. In this review, we summarized the effects of each stage of lignocellulosic biorefinery on nutrients and possible inhibitors, analyzed the huge differences in nutrient retention and inhibitor generation among various biorefinery strategies, and emphasized that all steps in lignocellulose biorefinery need to be considered comprehensively to achieve maximum nutrient retention and optimal control of inhibitors at low cost, to provide a reference for the development of biomass energy and chemicals.

Process design for acidic and alcohol based deep eutectic solvent pretreatment and high pressure homogenization of palm bunches for nanocellulose production

This research aimed to study on nanocellulose production from palm bunch using process design and cost analysis. Choline chloride based deep eutectic solvent pretreatment was selected for high-purity cellulose separation at mild condition, followed by nano-fibrillation using mechanical treatment. Three types of choline chloride-based deep eutectic solvents employing different hydrogen-bond donors (HBDs) namely lactic acid, 1,3-butanediol and oxalic acid were studied. The optimal cellulose extraction condition was choline chloride/lactic acid (ChLa80C) pretreatment of palm empty bunch at 80 °C followed by bleaching yielding 94.96%w/w cellulose content in product. Size reduction using ultrasonication and high-pressure homogenization produced nanocellulose at 67.12%w/w based on cellulose in raw material. Different morphologies of nanocellulose were tunable in the forms of nanocrystals, nano-rods and nanofibers by using dissimilar deep eutectic solvents. This work offered a sustainable and environmentally friendly process as well as provided analysis of DES pretreatment and overview operating cost for nanocellulose production. Application of nanocellulose for the fabrication of highly functional and biodegradable material for nanomedicine, electronic, optical, and micromechanical devices is achievable in the near future.

Preparation of spherical porous carbon from lignin-derived phenolic resin and its application in supercapacitor electrodes

Lignin is the most abundant aromatic biomass resource in nature and is the main by-product of paper industry and biorefinery industry, which has the characteristics of abundant source, renewable and low cost. Deep eutectic solvents (DES) are a nascent environmentally friendly solvent option that is gaining traction. DES composed of p-toluenesulfonic acid and choline chloride is used for batch treatment of alkaline lignin, and the bio-oil obtained is ternary polymerized with formaldehyde and phenol to obtain lignin phenolic resin. The porous carbon material is produced through a two-step carbonization process, utilizing phenolic resin derived from lignin as the primary source of carbon. The morphology and composition of the carbon were analyzed by SEM, TEM, XRD, TGA, XPS and Raman spectroscopy, the specific surface area and pore size distribution were analyzed by BET. The results showed that the specific surface area of the lignin-based phenolic resin was significantly higher than that of the pure phenolic resin carbon, and the porous carbon material that was acquired demonstrated a specific surface area of as much as 1026 m2/g. In the three-electrode system, the specific capacitance of DLPFC can reach 245.8 F/g (0.25 A/g), with a very small decrease in the value of specific capacitance at 10,000 cycles, with a retention of 97.62% (10 A/g). The porous carbon demonstrated a specific capacitance of 112.4 F/g at a current density of 0.5 A/g, and the capacitance retention rate could still reach 98.8% after 5000 charge/discharge cycles, with high cycling stability (in the two-electrode system). The prepared symmetrical supercapacitors exhibited high energy density and power density of 3.9 Wh/kg and 125.0 W/kg. The results suggest a new idea of high value-added application of lignin phenolic resin for high-performance supercapacitor electrodes.

Density-oriented deep eutectic solvent-based system for the selective separation of polysaccharides from Astragalus membranaceus var. Mongholicus under ultrasound-assisted conditions

The water extraction and ethanol precipitation method is an extraction method based on the solubility characteristics of polysaccharides that offers wide applicability in the extraction and separation of plant polysaccharides. However, this method leads to large amounts of proteins, nucleic acids, pigments, and other impurities in the polysaccharides products, which makes downstream purification complicated and time-consuming. In this study, a green, high-density natural deep eutectic solvents was used for the high-purity extraction and separation of polysaccharides from Astragalus membranaceus (Fisch) Bge. var. Mongholicus (Bge.) Hsiao roots under ultrasound-assisted conditions. In this study, 16 different natural deep eutectic solvents were designed to screen the best solvent for extracting Astragalus polysaccharides (APSs). Based on the yield and recovery of APSs, a natural deep eutectic solvents composed of choline chloride and oxalic acid with a molar ratio of 1:2 was selected. The related factors affecting polysaccharides extraction and solvent precipitation were investigated. To improve the operating methodology, single-factor trials, a Plackett-Burman design, and a Box-Behnken design were used. The optimal extraction process conditions were obtained as follows: water content of 55%, liquid-solid ratio of 24 mL/g, ultrasonic irradiation time of 54 min, ultrasonic irradiation temperature of 50 °C, ultrasonic irradiation power of 480 W, ethanol precipitation time of 24 h, and ethanol concentration of 75%. Under optimal extraction conditions, the recovery of APSs was 61.4 ± 0.6 mg/g. Considering the special matrix characteristics of A. membranaceus var. Mongholicus roots, physical-technology-based ultrasonic waves promote penetration, and the mass transfer function also solves the bottleneck of high-viscosity deep eutectic solvents in the extraction stage. In comparison with the conventional method, the proposed method based on deep eutectic solvents isolation can significantly increase APSs recovery, which is beneficial to simplifying the process of polysaccharides purification by using solvent properties to separate extracts and reduce impurities in APSs.

Production of nanocellulose using acidic deep eutectic solvents based on choline chloride and carboxylic acids: A review

Nowadays, nanocellulose production processes with numerous merits of green, eco-friendly, and cost-effective are in urgent need. Acidic deep eutectic solvent (ADES), as an emerging green solvent, has been widely applied in the preparation of nanocellulose over the past few years, owing to its unique advantages, including non-toxicity, low cost, easy synthesis, recyclability, and biodegradability. At present, several studies have explored the effectiveness of ADESs in nanocellulose production, particularly those based on choline chloride (ChCl) and carboxylic acids. Various acidic deep eutectic solvents have been employed, with representative ones such as ChCl-oxalic/lactic/formic/acetic/citric/maleic/levulinic/tartaric acid. Herein, we comprehensively reviewed the latest progress of these ADESs, focusing on the treatment procedures and key superiorities. In addition, the challenges and outlooks of ChCl/carboxylic acids-based DESs implementation in the fabrication of nanocellulose were discussed. Finally, some suggestions were proposed to advance the industrialization of nanocellulose, which would help for the roadmap of sustainable and large-scale production of nanocellulose.

DES: their effect on lignin and recycling performance

Lignocellulosic biomass raw materials are renewable resources with abundant reserves in nature, and have many advantages, such as being green, biodegradable and cheap. Lignin, one of the three significant components of lignocellulose, possesses a chemical structure rich in phenylpropane and is a primary aromatic resource for the bio-based economy. For the extraction and degradation of lignin, the most common method is the pretreatment of lignocellulose with deep eutectic solvents (DES), which have similar physicochemical properties to ionic liquids (ILs) but address the disadvantages associated with ILs (DES have the advantages of low cost, low toxicity, and non-flammability). In lignocellulose pretreatment, a large amount of solvent is generally required to achieve the desired effect. However, after treatment, a substantial volume of solvent will be wasted, and thus, the problem of the recovery and reuse of DES solution needs to be adequately solved. The methods and mechanisms of perfect DES regeneration will be discussed from the perspective of the elemental composition and features of DESs in this review, which will also outline the present DES recovery methods, such as rotary evaporation, membrane separation, freeze-drying, electrodialysis, etc. The detailed process and the advantages and disadvantages of each method since 2018 are introduced in detail. Future DES recovery methods have been prospected, and the optimization of the functional properties of DESs after recovery is discussed. It is expected to find a convenient and efficient application method for DES extraction or degradation of lignin with low energy and low cost.