Deep Eutectic Solvent Treatment Research Articles

Total Utilization of Components Contained in Coconut Husk by Microwave-Assisted Thermal Hydrolysis and Deep Eutectic Solvent Treatment

Total Utilization of Components Contained in Coconut Husk by Microwave-Assisted Thermal Hydrolysis and Deep Eutectic Solvent Treatment

Comparison of the Effects of NaOH and Deep Eutectic Solvent Catalyzed Tobacco Stock Lignin Isolation: Chemical Structure and Thermal Characteristics

Uncovering the structure of lignin from biorefinery has an important effect on lignin catalytic depolymerization and the production of bioenergy. In this study, two biorefinery lignins were isolated from tobacco stalks via alkaline and deep eutectic solvent (DES) catalyzed delignification processes, and the lignin heterogeneity structural characteristics were elucidated by gel permeation chromatography, 2D-HSQC, FT-IR, etc., to understand the relationship between the structure and the thermal characteristics of lignin. It was found that the lignins presented various structural characteristics and components, in which the predominant interunit linkages of black liquor lignin are β-O-4 and β-β linkages, and the β-O-4 linkages disappeared by DES treatment. DES lignins exhibited lower molecular weights and yields than black liquor lignin. Thermogravimetric analysis and fixed-bed pyrolysis were also performed to investigate the lignin thermal behavior. The results show that the DES approach can improve the bio-oil production from lignin and highlight the potential of DES lignin as a promising feedstock in the lignin pyrolysis process. This work provides a valuable example of the conversion of biorefinery lignin into pyrolysis products.

Insights into the Chemical Structure and Antioxidant Activity of Lignin Extracted from Bamboo by Acidic Deep Eutectic Solvents.

Deep eutectic solvents (DESs) composed of choline chloride as hydrogen bond acceptors (HBAs) and six organic acids as hydrogen bond donors (HBDs) were used to extract lignin from bamboo (Phyllostachys edulis (Carrière) J. Houz.). The structures of the DES-extracted lignin samples were analyzed by Fourier-transform infrared spectroscopy (FT-IR), UV-visible spectroscopy (UV-vis), thermogravimetric analysis (TG), and gel permeation chromatography (GPC) to investigate the relationship between the chemical structure of lignin and its antioxidant activity. The results showed that DES treatment removed a large portion of the lignin (73.37-86.38%) from bamboo, and the chemical structure of lignin was changed due to the use of different types of HBDs. The extracted lignin exhibited good UV-vis light shielding properties, thermal stability, and antioxidant activity. Moreover, the total phenolic hydroxyl content of lignins was positively correlated with their antioxidant activity, while the molecular weight of lignins was negatively correlated with their antioxidant activity. Notably, lignin extracted with choline chloride-p-toluenesulfonic acid had the highest phenolic hydroxyl content and lower molecular weight, showing the strongest antioxidant activity (IC50DPPH = 417.69 μg/mL, IC50ABTS = 58.62 μg/mL). This study confirms the high thermal stability, excellent antioxidant activity, and UV shielding properties of lignin extracted with choline chloride-organic acid DESs, suggesting its potential application in the fields of antioxidants and material modifiers.

Modified lignin by deep eutectic solvent as a novel coupling agent for wood-plastic composites

In this work, the influence of modified lignin by Deep Eutectic Solvent (DES) as a novel bio coupling agent on the various properties of wood flour- polypropylene composites (WPCs) was investigated. For this purpose, extracted lignin from Bagasse Soda black liquor was modified with Choline chloride–ZnCl2 deep-eutectic solvent (ChCl–ZnCl2 DES) and then different ratios of unmodified and modified lignin (0, 1, 3 and 5 wt%) were added to the wood flour/polypropylene mixture. Different properties of lignin after modification by DES along with physical and mechanical properties of the manufactured composites were measured according to the relevant standard methods. The FTIR analysis indicated that DES- modified lignin has a higher proportion of phenolic hydroxyl groups (1213 cm−1) and a lower one of methoxy groups (2854 cm−1) when compared to virgin lignin. DSC analysis also showed that the glass transition temperature (Tg) of lignin decreased from 90 °C to 80 °C by DES treatment. Based on the results obtained, the physical and mechanical properties of WPCs were continuously improved by increasing the modified lignin content from 1 to 5 wt%. The composites with DES-treated lignin presented lower water absorption and thickness swelling as well as higher flexural, tensile and impact properties compared to those prepared with unmodified lignin at the same fixed level of lignin. Moreover, based on the finding of this research, the composites with 5 wt% DES-treated lignin have relatively better physical and mechanical properties than those made from 2 wt% maleic anhydride polypropylene (MAPP) as a control sample. Modification of lignin with DES improves its uniform dispersion in the polymer matrix according to Scanning Electron Microscopy (SEM) images.

Nanocellulose separation from barley straw via ultrasound-assisted choline chloride – Formic acid deep eutectic solvent pretreatment and high-intensity ultrasonication

The present study aims at investigating the application of ultrasound assisted choline chloride (ChCl) – formic acid (FA) deep eutectic solvent (DES) pretreatment of Barley straw. In addition, the efficiency of a wet grinding followed by high intensity ultrasound (HIUS) treatment for production of cellulose nanofibers (CNF) has been evaluated. The DES (using ChCl: FA at 1:9 M ratio) treatment at 45 kHz ultrasound frequency and 3 h of treatment duration resulted in 84.68 ± 1.02 % and 82.96 ± 0.79 % of lignin and hemicellulose solubilisation, respectively. The purification of DES treated solid residue resulted in cellulose with more than 90 % purity. Further, 10 min of wet grinding followed by 40 min of HIUS treatment resulted in more than 80 % nano-fibrillation efficiency. The produced CNF had diameters less than 100 nm in number size distribution and type I cellulose structure. This study confirmed that the developed process offers a sustainable method for producing nanocellulose from agricultural waste.

Enzymatic hydrolysis of chitinous wastes pretreated by deep eutectic solvents into N-acetyl glucosamine

In this study, we present an efficient and green extraction-pretreatment integrated approach for enhancing enzymatic conversion of chitinous wastes into N-acetyl-d-glucosamine (GlcNAc). Firstly, the enzyme cocktail containing a chitinase CmChi1 and a N-acetyl glucosaminase CmNAGase were constructed for hydrolyzing chitin into sole GlcNAc. Secondly, deep eutectic solvent (DES), consisting of choline chloride and glycollic acid was used to treat chitinous wastes. Under optimal conditions, chitin yield reach to 72 % with a purity of 98 %. Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction analysis revealed that the crystallinity and thermal stability of the obtained chitin decreased upon DES treatment without alteration of the chemical structure or deacetylation. Finally, the concentration of GlcNAc was increased 2–6 folds by enzymatic hydrolysis of DES-treated chitinous wastes (including shrimp shell, crab shell, ganoderma spores wall, and mycelium). The process provides a promising strategy for degrading chitinous wastes to produce high valued GlcNAc.

Model-based process intensification of deep eutectic solvent treatment of eucalyptus slabs for lignin extraction and pulp production

This work revealed the reaction characteristics in the delignification process of eucalyptus slabs catalyzed by acidic deep eutectic solvent (benzyltriethylammonium chloride/formic acid) from the perspective of heterogeneous reactions. The limitation of internal diffusion on delignification process cannot be ignored. Afterwards, a kinetic model based on cell wall structure was proposed to describe the relationship between the delignification degree and reaction conditions, and it also hold excellent predictive ability for lignin removal, carbohydrate retention and solid residue yield. Compared with other reported kinetic models, this novel model not only took into account all operational parameters of reaction process, but also can be applied to the entire reaction process without the need for segmentation. Besides, an essential requirement based on the developed model was a 44.40 wt% formic acid concentration and a temperature of 130 °C, when the purpose of DES treatment was pulping. Generally, this work could provide guidance on process adjustments and product quality control during the DES processing.

Effect of Treatment Time on Deep Eutectic Solvent Treatment of Scots Pine Wood

Aim of study: The influence of the treatment time (1 hour, 2 hours, and 3 hours) on the deep eutectic solvent (DES) treatment of Scots pine (Pinus sylvestris L.) wood is investigated in this study. 
 Area of the study: Determination of DES performance on the Scots pine wood chemical structure.
 Material and methods: Choline chloride (ChCl) and lactic acid (LA) mixture with molar ratio of 1:10 (w:w) was used as a DES solvent. Treatments were carried out in an autoclave at 121 °C. The effects of DES treatment on the properties of wood and lignin samples of Scots pine were determined according to the relevant standards.
 Main results: The delignification ratio, lignin purity, and lignin yield in the 3h-treated sample were determined to be 79.78%, 86.43%, and 82.48%, respectively. The crystallinity index (CrI) was increased from 55.87% to 71.58% with 3 h DES treatment. Brunauer-Emmett-Teller (BET) analysis results showed that the surface area of the sample increased with 3-h DES treatment (from 3.095 m2/g to 3.621 m2/g). The 1-hour DES-treated sample yielded the lightest colored lignin (L*: 71.62). 
 Research highlights: Treatment time of Scots pine wood during DES treatment has a significant effect on the wood and lignin properties

EFFECT OF DEEP EUTECTIC SOLVENT PRETREATMENT ON DEVULCANIZATION OF WASTE RUBBER POWDER

ABSTRACT The recycling of waste rubber is very important for environmental protection, but the compatibility problem restricts the recycling and application of waste rubber powder (WRP). Devulcanization of WRP has been proven to be an effective method to improve the solubilization effect. The use of environmentally friendly nontoxic solvents can not only improve the devulcanization effect but also avoid secondary pollution. Thus, in this article, an environmentally friendly deep eutectic solvent (DES) is first prepared and then applied to the devulcanization treatment of WRP. The results show that the prepared DES has a positive devulcanization effect, and the devulcanization rate can reach 50%. The devulcanization mechanism can be divided into two aspects: (1) adsorption and removal of sulfur-containing low-molecular compounds and (2) destruction of the crosslinking structure and improvement of fluidity. Observation of the microstructure showed that the rougher the surface of the desulfurized rubber powder, the more conducive to the crosslinking reaction with the matrix material to form a uniform whole. The devulcanization mechanism of DES is divided into destroying the sulfur-containing cross-linked structure and adsorbing the sulfur-containing low-molecular compounds. The surface of WRP after DES treatment is rougher and more porous, which is beneficial to the crosslinking reaction with the matrix material. Finally, the optimum process conditions for the de-crosslinking effect are determined by orthogonal test as follows: liquid-solid ratio 15∶1, temperature 120°C, time 0.5 h.

Hydrophilic Modification of Polylactic Acid Fiber and the Usage of Natural Dye for Multi-Levered Improvement of the Fabric Staining Depth and the Stability Effect.

Polylactic acid (PLA) fiber is a degradable material with good environmental friendliness for textile applications. However, the main problems of difficult dyeing of PLA fibers were: high crystallinity to the adsorption of dyes, more ester and methyl groups producing non-hydrophilic problems, long chains making dyes difficult to penetrate, and producing a low dyeing rate. Here, we attempted to change the crystallinity of the PLA fiber to a lower degree from hydrophobic to hydrophilicity property variation, destroy the long chain structure to grant more staining sites, and improve the PLA fiber staining depth and the resilience dyeing effect with deep eutectic solvent (DES) treatment and natural dyes. We discovered that a controlled DES treatment process could make PLA fibers less crystallized, help amorphous areas form, and break up long chains, which lead to more dye sites. After DES treatment, the crystallinity decreased from 56.12 to 29.86%, and the instantaneous water contact angle decreased from 108.79 to 64.39°. The DES-treated PLA fabric exhibited a higher K/S value of 15.14 for natural dyes under specific conditions. The fabric, which had remarkable fastness characteristics and wash resistance, could endure frequent laundering and fulfill the demands of everyday use. Moreover, the fabric had good antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans and possessed a certain level of biocompatibility with fibroblasts. This DES treatment and natural dye combination method offered a new strategy for improving PLA fabric staining depth and color fastness, making it a promising option for low-carbon environmental protection in the textile industry.

Eco-friendly regeneration of lignin with acidic deep eutectic solvent for adsorption of pollutant dyes for water cleanup

In this study, a simple and eco-friendly method was used to treat alkaline lignin with an acidic deep eutectic solvent (DES) to obtain regenerated lignin for the efficient adsorption of pollutant dyes from aqueous environment. Based on the yield and adsorption capacity of the sorbent for these dyes, conditions such as the type and concentration of DES component, solid-to-liquid ratio, reaction time, and temperature were optimized. By characterizing and comparing alkali lignin with regenerated lignin, a series of reactions were demonstrated to occur during the DES treatment process. The performance and mechanism of methylene blue and rhodamine B adsorption on regenerated lignin were studied systematically, and the maximum adsorbed amounts were 348.29 and 551.05 mg/g at 323 K, respectively. This study provides a new strategy for the green preparation of functionalized lignin and its use in the water pollutant treatment.

Structural changes of poplar lignin during the ternary deep eutectic solvent (DES) treatment and synergetic alkali-DES treatment

Expenditure isolation of lignin and the understanding of its structural variations during different isolation process is essential for lignin high-value utilization. A green DES consisted with choline chloride (ChCl), ethylene glycol (EG) and 4-chlorobenzene sulfonic acid (4-Cl-BSA) was proposed for rapid lignin separation from poplar in this study. About 97.01% of lignin and 87.41% of hemicellulose were removed while the cellulose preservation achieved 95.02% under 90 °C for 30 min using this DES with the molar ratio of 1:2:0.7 (ChCl: EG: 4-Cl-BSA). The percentage of β-O-4 linkages, molecular weight and associated sugar content of DES lignin declined steadily with the enhancement of treatment severity. Additionally, the pre-extraction of hemicellulose through alkali treatment on subsequent lignin separation and lignin structural variations was also elucidated. The results suggested that alkali pretreatment opened the channels of the cell wall and increased DES permeability to the material, enhancing the DES separation of lignin. It also promoted the cleavage of the β-O-4 and PB linkages during followed DES separation lignin, and reduced the molecular weight and thermal stability of isolated DES lignin. In addition, the integrated DES lignin displayed higher purity and S/G ratio compared to lignin obtained from direct DES treatment. The Py-GC/MS results indicated the obtained DES lignin was suitable for phenolic compounds production and the total phenolic compounds yield ranged from 41.56% to 62.42%. This study provides insight into lignin structural transformation during different pretreatment and guides for dismantling cell walls.

Parametric studies on pretreatment of lignocellulosic biomass via deep eutectic solvents: Enhancing densified pellet quality

Densified pellets derived from lignocellulosic biomass are attractive candidates for alleviating energy constraints and replacing fossil fuels. However, the undesirable properties of lignocellulosic biomass and the resulting high costs of handling have hampered its widespread application. In the present study, we introduce a pretreatment strategy for lignocellulosic biomass to produce high quality densified pellets. In this process, the structure of lignocellulosic biomass was deconstructed and lignin was regenerated in situ, resulting in a homogeneous cellulose-lignin slurry. The resulting densified pellet exhibits higher density (up to ∼1200 kg/m3), strong mechanical strength (maximum increase to ∼12 N/mm2), better water resistance (decreased from 15% to 10%), and improved combustion characteristics (enhanced nearly twice). The improved performance indicates that the combination of deep eutectic solvent treatment with densification is an efficient way to develop processing schemes for sustainable and efficient utilization of lignocellulosic biomass.

Integrated understanding of acidic deep eutectic solvent choline chloride: Oxalic acid pretreatment to enhance the enzymatic hydrolysis of rape straw

Using choline chloride (ChCl) as hydrogen-bonded-acceptor (HBA) and oxalic acid (OA) as hydrogen-bonded-donor (HBD), deep eutectic solvents (DESs) with different HBD-to-HBA molar ratios were synthesized to pretreat rape straw (RS). The influence of DES treatment on the RS chemical composition, structure change, and enzymatic saccharification were explored. DESs with low molar ratio of HBD-to-HBA exhibited low viscosity, which enhanced the pretreatment efficiency. When HBA-to-HBD molar ratio was 1:3, the delignification and enzymatic digestion efficiency were only 60.6% and 41.8%. As the molar ratio of OA decreased, delignification and enzymatic digestion efficiency increased to 83.6% and 96% (ChCl:OA = 3:1, mol/mol). After pretreatment (severity factor LogR0 =2.66), the cellulose accessibility and crystallinity increased from 353.0 to 691.1 mg/g and 35.4–64.2%, respectively. The lignin surface area decreased from 596.3 to 201.9 m2/g. The significant increase in cellulose accessibility and the decrease in lignin surface area explained the efficient enzymatic hydrolysis efficiency.

Two birds, one stone: Deep eutectic solvent (DES) modified graphite felt electrode significantly improves performance of DES-electrolyte non-aqueous flow battery

In the past, non-aqueous redox flow batteries usually used organic solvents or ionic liquids as electrolytes. However, these two liquids are not suitable as electrolytes in terms of safety and production costs. Herein, we chose a deep eutectic solvent (DES) for non-aqueous redox flow battery. DES has been applied to play two functions in Fe/V non-aqueous redox flow battery: commercial graphite felt electrode is treated with DES and heat treatment for surface modification; DES also acts as a main electrolyte for the non-aqueous redox flow battery. While ensuring no external substances are introduced to produce side reactions, the electrode reaction kinetics are enhanced, and better cyclability is achieved. The modified treatment increases the number of oxygen-containing groups and defect sites on electrode surface. Electrode exhibits higher electrochemical activity and lower charge transfer resistance. In the full battery test, the maximum power density with modified electrode reaches 13.26 mW·cm−2, which is 114% higher than commercial graphite felt electrode. The energy efficiency reaches 90.50% and battery life is extended by 70.58% compared with commercial graphite felt electrode. This study has successfully improved the electrochemical performance of Fe/V DES redox flow battery and provides a novel idea for electrode modification.

Optimum Yield of Empty Fruit Bunches Cellulose Nanofibers by Deep Eutectic Solvent and Ultrasonication

AbstractCellulose nanofibers (CNFs) are extensively utilized as affordable, renewable materials. The conventional technique for making CNFs is time‐consuming, requires hazardous toxic chemicals, and consumes enormous amounts of energy. CNFs from empty fruit bunches (EFB) were produced via deep eutectic solvent (DES) and ultrasonication. The DES treatment conditions were optimized using the central composite design (CCD) approach of response surface methodology (RSM). Analysis of variance (ANOVA) revealed that the reaction time, DES molar ratio, and temperature were all significant variables. The experimental results closely correspond to the theoretical model of CNFs yield. X‐ray diffraction (XRD) studies demonstrated that the crystallinity index of the CNFs increased significantly after sonication. It could be stated that DES treatment and ultrasonication were effective ways to successfully generate CNFs from EFB. This study may serve as foundation for high‐yield, industrial‐scale synthesis of nanocellulose using DES treatment.

Preparation of Dissolving Pulp by Combined Mechanical and Deep Eutectic Solvent Treatment.

Grasses are potential candidate to replace wood as a raw material for pulping and paper making, and several processes have been developed to produce grass pulp. In this study, wheat straw was used as raw material, and the possibility of sequential treatment with a mechanical method and deep eutectic solvent (DES) to prepare high-quality dissolving pulp was explored. Firstly, the wheat straw was mechanically treated, and then the wheat straw was delignified using a choline chloride-lactic acid deep eutectic solvent. The results showed that the optimal treatment conditions of deep eutectic solvent were 110 °C, 6 h, and a solid-liquid ratio (ratio of pulp to DES) of 1:40. The removal rate of lignin was 82.92%, the glucose content of pulp was increased by 11.42%. The DES recovery rate was further calculated, and the results showed that the DES recovery rate was more than 50% with rotary evaporation. The pulp viscosity after bleaching was 472 mL/g, and the α-cellulose accounted for 81.79%. This treatment has advantages in biomass refining, and the total utilization rate of wheat straw reaches 72%. This study confirmed that combined mechanical and deep eutectic solvent treatment can effectively remove lignin from wheat straw to produce high-quality wheat straw dissolving pulp.

Extracting dialdehyde cellulose nanocrystals using choline chloride/urea-based deep eutectic solvents: A comparative study in NaIO4 pre-oxidation and synchronous oxidation

Dialdehyde cellulose nanocrystals (DCNC) are defined as C2 and C3 aldehyde nanocellulose, which can be used as raw materials for nanocellulose derivatization, owing to the high activity of aldehyde groups. Herein, a comparative study in NaIO4 pre-oxidation and synchronous oxidation is investigated for DCNC extraction via choline chloride (ChCl)/urea-based deep eutectic solvent (DES). Ring-liked DCNC with an average particle size of 118 ± 11 nm, a yield of 49.25 %, an aldehyde group content of 6.29 mmol/g, a crystallinity of 69 %, and rod-liked DCNC with an average particle size of 109 ± 9 nm, a yield of 39.40 %, an aldehyde group content of 3.14 mmol/g, a crystallinity of 75 % can be extracted via optimized DES treatment combined with pre-oxidation and synchronous oxidation, respectively. In addition, the average particle size, size distribution, and aldehyde group content of DCNC were involved. TEM, FTIR, XRD, and TGA results reveal the variation of microstructure, chemical structure, crystalline structure, and thermostability of two kinds of DCNC during extraction even though the obtained DCNC exhibiting different micromorphology, pre-oxidation, or synchronous oxidation during ChCl/urea-based DES treatment can be considered as an efficient approach for DCNC extraction.

The structure and properties of lignin isolated from various lignocellulosic biomass by different treatment processes

The structure and properties of lignin can vary depending on the type of lignocellulosic biomass it comes from and the separation techniques used, and also affects its suitability for different applications. In this work, the structure and properties of lignin isolated from moso bamboo, wheat straw, and poplar wood by different treatment processes were compared. Results show that deep eutectic solvent (DES) extracted lignin exhibits well-preserved structures (including β-O-4, β–β, and β-5 linkages), a low molecular weight (Mn = 2300–3200 g/mol), and relatively homogeneous lignin fragments (1.93 < PDI < 2.33) compared to dealkaline lignin (DL) and milled wood lignin (MWL). Besides, lignin samples extracted by DES have a regular nanostructure, higher carbon residue content (>40 %), and excellent antioxidant properties (the free radical scavenging index >20). Among the three types of biomass, the structural destruction of lignin in straw is the most obvious, which is due to the degradation of β-O-4 and β-β linkages during DES treatment. These findings can contribute to a better understanding of the structural changes that occur in various treatment processes from different lignocellulosic biomass, and help maximize the targeted development of their applications based on the characteristics of lignin.

Multistage treatment of bamboo powder waste biomass: Highly efficient and selective isolation of lignin components

Bamboo pulp and papermaking produce a lot of bamboo powder waste, and its resource utilization is of great significance for biomass refining and environmental protection. Here, we propose an integrated approach involving mechanical activation, hydrothermal extraction, and deep eutectic solvents (DESs) multiple delignification for the efficient separation of bamboo powder. Among seven carboxylic acids based DESs, choline chloride (ChCl)-lactic acid (La) DES (1:1) is the most effective, with over 78.0% lignin removal and 88.9% cellulose retained after mechanical-hydrothermal (180 °C, 5 h)-DES (110 °C, 12 h) treatment. Notably, 84.7% of delignification is achieved after three times of ChCl-La DES treatment at 70, 90, and 110 °C respectively. The delignification rate is negatively correlated with the amount of carboxyl group in the DESs. The lower the pKa value, the higher the delignification rate. Additionally, the selectivity for lignin is improved with decreasing solvent polarity. DES treatment effectively degrades the guaiacyl unit lignin fractions and disrupts several β-aryl-ether bonds (e.g., β-O-4, β-β, and β-5). Furthermore, DESs exhibit good recyclability, with less than 10% reduction in delignification after three cycles. Theory calculations confirm that ChCl-carboxylic acid DESs could compete with lignin to break hydrogen bonds in lignocellulosic biomass by providing their chloride, hydroxyl, and carboxyl groups. Overall, this study demonstrates the practical significance of multistage treatment for the effective fractionation of biomass into its three components.