Deep Eutectic Solvents Composition Research Articles

Biodiesel purification by novel green solvent based on choline chloride: Deep eutectic solvent

AbstractIn the typical biodiesel production process carried out by the wet method, large volumes of effluents are generated. The objective of this work was to evaluate and compare the use of a novel high efficiency deep eutectic solvent (DES), with the conventional solvent (hot water). The intense ionic interactions established with the formation of hydrogen bonds between DES and impurities, especially with OH groups, potentiated the use of DES, reducing the levels of moisture, free and total glycerol, and mono, di‐ and triglycerides, in accordance with the standards EN 14214 and ASTM D6751, and being more efficient than conventional purification in some cases. The use of triethylene glycol in the DES composition reduced the content of triglyceride, a poorly soluble molecule. Therefore, with a simple and efficient technique, this work presents the potential use of a new alternative green solvent, which can help reduce costs for biodiesel purification.

Effect of water on amine-based deep eutectic solvents (choline chloride + monoethanolamine): Structure and physicochemical properties

Water, can not only regulate the thermodynamic properties of deep eutectic solvent (DES), but also affect its supramolecular structure. Therefore, it is necessary and meaningful to study the effect of water on DES. In this work, amine functionalized DES (choline chloride + monoethanolamine) was successfully prepared, and the densities and viscosities of DES + H2O were measured from 293.15 K to 323.15 K. The effects of DES composition, water content and temperature on the excess molar volume, partial molar volume, apparent molar volume, limiting molar volume, coefficient of thermal expansion, viscosity deviation and activation energy for viscous flow were investigated. The hydration and structural changes of DES were analyzed. Additionally, the Redlich-Kister equation was used to correlate the excess properties of DES + H2O. Finally, a three-stage theory of effect of water on DES, namely the pure DES stage, the destruction stage and the thorough destruction stage, was proposed. Conclusively, it can be seen that an appropriate amount of water is very helpful to improve the properties of DES, otherwise the structural advantages of DES will be lost. It is hoped that this study will lay a foundation for the application of DES.

Application of multivariate linear regression models for selection of deep eutectic solvent for extraction of apigenin and luteolin from Chrysanthemum indicum L.

Among a variety of compounds presented in chrysanthemum, apigenin and luteolin are the two main components that play a major role in numerous biological activities of this herb. We aimed to obtain linear models showing the dependence of the yield of extraction of apigenin and luteolin on the composition of deep eutectic solvent and investigate the extraction of these two ingredients from Chrysanthemum indicum L. Two models showing the dependence of luteolin and apigenin concentrations on the composition of the solvent were established using a multilinear regression algorithm and were applied to screen 119 different solvents. After that, the extraction process was optimized using response surface methodology and an artificial neural network. Apigenin and luteolin were recovered from the extract by the combination of distillation and addition of water. The screening results on 119 solvents revealed that choline chloride-acetic acid (1:4) was the most suitable deep eutectic solvent. It was showed that both response surface methodology and the artificial neural network could accurately determine the optimal conditions of extraction of apigenin and luteolin from C. indicum L., including time of extraction (65 minutes), temperature of extraction (90°C) and water content (20%). By the combination of distillation and addition of water, apigenin and luteolin could be effectively recovered from the deep eutectic solvent extract with a recovery rate of over 80%. Deep eutectic solvent could be used as an effective green alternative to the conventional solvents for the extraction of bioactive compounds from plants.

A Review of the electrochemical corrosion of metals in choline chloride based deep eutectic solvents

Deep eutectic solvents (DESs) are a class of mixtures with melting points notably lower than those of their raw constituent components. These liquids have found a tremendously wide spectrum of applications in the last two decades of their research, so their contact and interaction with technical metals and alloys are inevitable. Therefore, the corrosivity of DESs towards metals is an extremely important topic. This review summarizes research efforts collected in the last two decades related to the corrosion rate of various metals in different DESs. Since the DESs are mainly composed of organic raw compounds, and by their physicochemical properties they may be regarded as a separate class of ionic liquids, the literature data about DESs corrosivity has been compared to the data related to the corrosivity of various organic solvents and ionic liquids as well. All the results gained until now show significantly low corrosivity of DESs. This observation is discussed in relation to the chemical composition of DESs. The absence of the oxidizing agents, the inhibitory action of organic ions and molecules, high viscosity and low electrical conductivity have been recognized as the main factors contributing to the low metal corrosion rate in DESs.

Behavior of quaternary ammonium salts and terpenoids-based deep eutectic solvents in aqueous phase

Numerous articles have been presented on efficient liquid–liquid extraction procedures from aqueous samples using deep eutectic solvents based on quaternary ammonium salts or natural terpenoids as hydrogen bond acceptors and fatty acids as hydrogen bond donors. However, precursors of these solvents are soluble in the aqueous phase and the composition of the solvents can be changed in the presence of water. In this research the stability and composition of deep eutectic solvents based on quaternary ammonium salts (tetrabutylammonium bromide and tetraoctylammonium bromide), terpenoids (menthol and thymol) and fatty acids (hexanoic, heptanoic, octanoic, nonanoic and decanoic acids) in aqueous phase were systematically investigated. It was shown that all studied two-component solvents are transformed into three-component solvents in the presence of water. Effects of hydrogen bond acceptors and donors type on formation of three-component solvents were investigated and discussed. It was established that, the ratio of aqueous and organic phases plays a key-role for stability of the solvents based on tetrabutylammonium bromide. The solvents based on terpenoids and tetraoctylammonium bromide remain stable in the wide range of phases ratios. In addition to the study of stability, changes in the physicochemical and extraction properties of ternary eutectic solvents in comparison with two-component solvents have been shown.

Anhydrous proton conductivity of sulfonated polysulfone/deep eutectic solvents (DESs) composite membranes: Effect of sulfonation degree and DES composition

The potential use of deep eutectic solvents (DESs) for anhydrous conductivity of sulfonated polysulfone membrane is presented. To this end, different molar ratios of sodium bromide as hydrogen bond acceptor (HBA) and ethylene glycol as hydrogen bond donor (HBD) are used for the synthesis of DESs. Two sulfonation degrees (DS) of 30 and 40% are also adjusted for the synthesis of sulfonated polysulfones. The synthesized DESs have suitable thermal stability as well as low viscosity to provide interconnected ionic pathways within the membranes. The proton conductivity of membranes is mainly influenced by the HBD/HBA molar ratio of DES as well as the DS of sulfonated polymer. The maximum proton conductivity of 301 mS/cm at 100 °C is obtained for the polymer with 40% DS containing a DES with a higher HBD/HBA molar ratio. The prepared composite membranes have great potential for fuel cell performance, especially in anhydrous conditions.

Efficient absorption of low partial pressure SO2 by deep eutectic solvents based on pyridine derivatives

Efficient and reversible absorption of SO2 by deep eutectic solvents (DESs) has drawn much attention in recent years. In this work, a new type of deep eutectic solvents (DESs) were synthesized via pyridine derivatives, nicotinamide, aminopyridines and hydroxypyridines, as the hydrogen bond donors (HBDs) with common quaternary ammonium salt ionic liquids (ILs) as hydrogen bond acceptors (HBAs). The studied DESs exhibited an attractive absorption behavior for SO2, especially for low concentration SO2. The 1-allyl-3-methylimidazolium chloride (AmimCl)/2-aminopyridine (2-NH2Py) (2:1) and 1-butyl-3-methylimidazolium chloride (BmimCl)/3-aminopyridine (3-NH2Py) (2:1) could capture 0.273 and 0.223 g SO2/g DES at 293 K and 1.0 kPa, respectively, surpassing that of most DESs and ILs in the present literature. The influence of DES composition, temperature and pressure on SO2 absorption performance was systematically investigated. Moreover, the absorption mechanism studied by nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopies indicated that the efficient absorption of SO2 was ascribed to the chemical interaction between the pyridine nitrogen atom and SO2.

Cover Feature: Deep Eutectic Solvents for High‐Temperature Electrochemical Capacitors (ChemElectroChem 21/2021)

The Cover Feature illustrates the wide temperature range for electrochemical capacitor operating with deep eutectic solvents (DES) as electrolytes. Right DES composition allows the electrolyte of satisfactory electrochemical and thermal stability to be obtained. More information can be found in the Article by A. Mackowiak et al.

Tunable and functional deep eutectic solvents for lignocellulose valorization

Stabilization of reactive intermediates is an enabling concept in biomass fractionation and depolymerization. Deep eutectic solvents (DES) are intriguing green reaction media for biomass processing; however undesired lignin condensation is a typical drawback for most acid-based DES fractionation processes. Here we describe ternary DES systems composed of choline chloride and oxalic acid, additionally incorporating ethylene glycol (or other diols) that provide the desired ‘stabilization’ function for efficient lignocellulose fractionation, preserving the quality of all lignocellulose constituents. The obtained ethylene-glycol protected lignin displays high β-O-4 content (up to 53 per 100 aromatic units) and can be readily depolymerized to distinct monophenolic products. The cellulose residues, free from condensed lignin particles, deliver up to 95.9 ± 2.12% glucose yield upon enzymatic digestion. The DES can be recovered with high yield and purity and re-used with good efficiency. Notably, we have shown that the reactivity of the β-O-4 linkage in model compounds can be steered towards either cleavage or stabilization, depending on DES composition, demonstrating the advantage of the modular DES composition.

Phase behavior of water-menthol based deep eutectic solvent-dodecane system

In the current work, two menthol-based hydrophobic deep eutectic solvents (DESs) have been synthesized to extract dodecane from water-dodecane emulsion at 298 K and atmospheric pressure. The equilibrium mixture produces two biphasic liquid-liquid equilibrium systems and one triphasic liquid-liquid-liquid equilibrium system. 1H NMR has been used to calculate the molar composition of each phase. For both the lauric and decanoic acid-based DES, the extract phase of biphasic region-1 is rich in DES; whereas the raffinate phase is predominantly water. However, for the biphasic region-2, the extract phase is the dodecane rich phase and raffinate phase is the mixture of DES and dodecane having a dominant composition of DES. In case of triphasic region, i.e. top phase consists of dodecane and the bottom phase is only water. The middle phase becomes an emulsion where DES is the dominant component. The selectivity analysis in the triphasic region proves that both the DESs have high selectivity to extract dodecane from the water-dodecane microemulsion. The experimental mole fractions are correlated with genetic algorithm (GA) promoted NRTL and UNIQUAC models to predict the phase behavior. An average overall root means square deviation (RMSD, %) of 0.174% is observed for the biphasic region and 0.048% for the triphasic employing GA-NRTL model. GA-UNIQUAC predicts an average overall RMSD of 0.340% for biphasic regions and 0.129% for the triphasic region.

Processing of anode slime with deep eutectic solvents as a green leachant

This paper describes an efficient process of recovering valuable metals from a copper anode slime sample using green chemicals such as choline chloride (ChCl) based deep eutectic solvents (DESs). The leaching agents include ChCl-urea, ChCl-ethylene glycol, ChCl-urea-ethylene glycol and ChCl/urea-deionized water in a 1:2, 1:2, 1:0.5:1.5, and 1:1 ratio, respectively. Prior to leaching experiments, chemical and mineralogical characterization of copper anode slime was performed. Considerable amount of precious metals was detected in the copper anode slime by chemical analysis. The main phases of copper anode slime detected by XRD and SEM/EDX analysis were namely Cu2O, SnO2, and, PbSO4. After leaching experiments, 97% of copper was recovered from the copper anode slime using ChCl-urea under an optimum condition at 95 °C of reaction temperature, 4 h reaction duration and, 1/25 g/mL solid/liquid ratio. The results showed that 91% of silver was extracted from the anode slime under the optimum condition with ChCl-urea DES composition, 95 °C reaction temperature, 48 h reaction duration, and 1/10 solid/liquid ratio. Gold was not leachable in the experiment using ChCl based DES with hydrogen bonding reagents such as urea and ethylene glycol. Moreover, the results revealed that PbSO4 was very soluble in DES prepared by ChCl and urea.

Deep eutectic solvent-immobilized PVDF-HFP eutectogel as solid electrolyte for safe lithium metal battery

A novel cheap eutectogel (ETG) membrane based on the deep eutectic solvent (DES) immobilized poly (vinylidene fluoride-hexafluoro propylene) (PVDF-HFP) is proposed as a solid electrolyte for safe lithium metal batteries in this study. The composition of DES is optimized, which is prepared by mixing the N-methylacetamide (NMAC) and the lithium bis [(trifluoromethyl)sulfonyl]imid (LiTFSI) with a molar ratio of 4:1. The eutectogel is formed by incorporating 70 wt% DES into the PVDF-HFP, which is non-flammable and shows excellent mechanical properties. This ETG membrane electrolyte with a thickness about 25 μm possess a high ionic conductivity (3.05 × 10−4 S cm−1) at room temperature and a wide electrochemical stability window (~5 V). The Li//ETG//LiFePO4 full cells deliver an acceptable discharge capacity of ~133.9 mAh g−1 at 0.1C and room temperature after 100 charge-discharge cycles. The ETG membrane electrolyte can also endow the Li//ETG//LiFePO4 pouch cell with flexibility and withstanding abuse operations, like nail penetration and cutting. We expect that the flexible and non-flammable eutectogel membrane will have implications for the use of DES based ionic liquids in the synthesis of advanced solid-state electrolytes for safer lithium batteries.

Binary and ternary deep eutectic solvent mixtures: Influence on methylene blue electropolymerisation

Binary and ternary deep eutectic solvent (DES) mixtures based on choline chloride, with ethylene glycol, oxalic acid, urea and fructose, were used for the first time as media for the electropolymerisation of poly(methylene blue) (PMB) on glassy carbon electrodes (GCEs) and GCEs modified with multiwalled carbon nanotubes (MWCNTs). The influence of different parameters such as DES composition, the presence of MWCNTs and/or of perchlorate dopant, on the polymer film properties was evaluated. The polymer films electrodeposited in the different media were characterized by cyclic voltammetry and different voltammetric characteristics were observed depending on the electropolymerisation conditions. This knowledge was used to determine the best binary and ternary mixtures for polymer growth, with a view to electrochemical sensor applications. The PMB-based modified electrode with the best characteristics was tested for ascorbate sensing in order to demonstrate the usefulness of this platform.

Application of deep eutectic solvents as a green and biodegradable media for extraction of anthocyanin from black carrots

Deep eutectic solvents (DESs) not only could keep a high extraction efficiency, but also could easily be applied to pharmaceutical and food products. This study aimed to set out an eco-friendly technique for the anthocyanin extraction from natural sources. In this study, DESs coupled with ultrasound-assisted extraction (UAE) were considered as an alternative green method to classical applications. The choline chloride-based DESs was prepared with the hydrogen bond donor. The conventional, UAE and DES extraction methods were studied and compared. Citric acid was selected as the most promising hydrogen bond donor for the preparation of DES. The results showed that the biodegradability of all tested DESs was >80% after 28 days. Based on the analyses, it could therefore be assumed that all of the analysed DESs were biodegradable green solvents. The results of FT-IR revealed that pure choline chloride demonstrated several functional groups and many of these functional groups coexisted after DES formation. Thermogravimetric analysis (TGA) showed that all the DESs and their components were degraded in a single stage and the polymeric colour ratio was lower if acid was present in the DES composition. The results indicated that the developed method could be regarded as a sustainable, effective, and green approach for anthocyanin extraction.

Characterization of Electrode-Electrolyte Interfaces in Deep Eutectic Solvents

Deep eutectic solvents (DESs), compromised of hydrogen bond donors and acceptors, are concentrated electrolytes with extremely low volatility and tunable physical properties, and therefore they are promising for large scale energy storage. The electrode-electrolyte interfaces of concentrated and complex electrolytes such as DESs have not been rigorously studied. Owing to the similarity of DESs to ionic liquids (ILs) where a camel shape potential-dependent capacitances have been reported with significant deviations from dilute electrolytes, it will be critical to understanding the DES behavior near polarized surfaces to inform electrochemical kinetics. In this work, the excess charge accumulation of mixtures of choline chloride and ethylene glycol with 1:2 (Ethaline DES composition), 1:4 and 1:6 molar ratios are probed on silver and glassy carbon electrodes via electrochemical impedance spectroscopy. To study the surface species and changes with applied potential, in-situ surface-enhanced Raman spectroscopy was employed on an electrochemically roughened silver substrate as the electrode. Results from these studies suggest Ethaline DES is different than most ILs and present u-shaped differential capacitance and more in line with regular electrolytes. We will present the results from our ongoing studies of the electrode-DES interfaces outlining the impact of composition and electrode material.

Phytomass Valorization by Deep Eutectic Solvents—Achievements, Perspectives, and Limitations

In recent years, a plethora of extraction processes have been performed by a novel class of green solvents known as deep eutectic solvents (DESs), possessing several environmental, operational, and economic advantages proven by experience when compared to organic solvents and ionic liquids. The present review provides an organized overview of the use of DESs as extraction agents for the recovery of valuable substances and compounds from the original plant biomass, waste from its processing, and waste from the production and consumption of plant-based food. For the sake of simplicity and speed of orientation, the data are, as far as possible, arranged in a table in alphabetical order of the extracted substances. However, in some cases, the isolation of several substances is described in one paper and they are, therefore, listed together. The table further contains a description of the extracted phytomass, DES composition, extraction conditions, and literature sources. With regard to extracted value-added substances, this review addresses their pharmacological, therapeutic, and nutritional aspects. The review also includes an evaluation of the possibilities and limitations of using DESs to obtain value-added substances from phytomass.

Deep Eutectic Solvent Extraction of High-Purity Lignin from a Corn Stover Hydrolysate.

A lactic acid/chlorine chloride-based deep eutectic solvent (DES) was used for the extraction of high-purity lignin (up to 94.7 %) in high yield (up to 75 %) from the hydrolysis/fermentation residue corn stover hydrolysate (CSH), which was generated from a pilot-plant-scale biorefinery. A range of extraction conditions were investigated, which involved varying reaction temperature, time, and DES composition. The relationship between lignin yield, purity, and structural characteristics with DES treatment conditions was determined. The extraction of high-purity lignin from hydrolysis/fermentation residues presents a promising approach for enhancing the economic feasibility of a lignocellulose biorefinery. It was also determined that DES extraction can produce lignin with a controlled range of molecular weight and functional group content.

Heteroatom-doped Porous Carbon Nanosheets Derived from Green Deep Eutectic Solvents for High-performance Micro-supercapacitors

This study reports a facile and green preparation of heteroatom-doped porous carbon nanosheets derived from deep eutectic solvents (DES). N-doped or N, S-co-doped carbon porous nanosheets are produced by varying the composition of glucose-based DES followed by a simple KOH activation, which show highly improved capacitances. Besides, micro-supercapacitors based on N-doped carbon nanosheets exhibit a specific capacitance of 23.2 mF cm−2 at 0.2 mA cm−2, which is among the best compared to the results reported in the literature.

Ultrasound-assisted hydrophobic deep eutectic solvent based solid-liquid microextraction of Sudan dyes in spice samples.

An environmentally friendly, simple method was carried out with the help of an ultrasonic assisted solid-liquid microextraction technique using a new deep eutectic solvent (DES) for the extraction and determination of Sudan dyes (I-IV) in spice samples. In this method, parameters affecting the optimization were researched and optimized such as DES composition, DES volume, ultrasonic time, temperature and, centrifuge time. The analytical performance of the developed method was quite satisfactory, the R2 values were higher than 0.9989, and the limits of quantification were <1.17μgg-1. Two different concentrations (10-50μgg-1) were spiked to Chili peppers, paprika, cumin and sumac spices for the applicability and accuracy of the developed microextraction method. Some of these spices were found to contain Sudan I and IV dyes. The recovery values for spiked samples were found to be between 85.55% and 99.29% and relative standard deviations were found to be <3.17% when using a 10μgg-1 Sudan dyes concentration. The results showed that the developed method can be successfully applied for extraction and determination of Sudan dyes in spice samples.

Deep eutectic solvent-based hollow fiber liquid-phase microextraction for quantification of Q-markers of cinnamic acid derivatives in traditional Chinese medicines and research of their plasma protein binding rates

A deep eutectic solvent-based hollow fiber liquid-phase microextraction was proposed and coupled with high performance liquid chromatography-ultraviolet detection for the quantification of four cinnamic acid derivatives (caffeic acid, p-hydroxycinnamic acid, ferulic acid, cinnamic acid) in traditional Chinese medicines and research of their plasma protein binding rates. Also, the extraction mechanism of target analytes and the determination mechanism of their plasma protein binding rate by the procedure are both explored and illustrated. In this study, the variables affecting the experiment procedure, including the type and composition of deep eutectic solvent, sample phase pH, salt amount, extraction temperature, stirring rate, extraction time, and incubation time of active compound in plasma (i.e., binding equilibrium time between active compound and plasma protein) were investigated and optimized. Under the optimum conditions, enrichment factors of 82.4, 105.9, 88.8, 127.1 for caffeic acid, p-hydroxycinnamic acid, ferulic acid and cinnamic acid, satisfactory linear ranges (r2 ≥ 0.9985), low detection limits (0.1–0.3 ng/mL), acceptable precisions with relative standard deviations (0.7%–6.1%) and recoveries (between 86.7% and 110.5%) were obtained. The feasibility of the proposed method was evaluated by the determination of four analytes in Chinese medicinal samples and research of their plasma protein binding rates. The results indicated that the developed method is eco-friendly, easy-to-handle, and has the major advantages of high-preconcentration factor and remarkable clean-up ability.