Viscosity Of Deep Eutectic Solvents Research Articles

Influence of water on the properties of hydrophobic deep eutectic solvent

Deep eutectic solvent (DES) shows excellent absorption performance in the field of CO2 capture. It is considered as a new green absorption solvent to replace monoethanolamine. In the industry, the presence of water not only affects the structural stability of the solvent, but also affects its thermophysical properties. In this work, three kinds of hydrophobic DES were prepared. Based on the study of their structural characteristics and thermal stability, the density and viscosity of DES with water mixture were measured in the temperature range of 298.15 ∼ 338.15 K at atmospheric pressure. It was demonstrated that the trace water did not destroy the structure of DES, but it formed hydrogen bonds with DES. The increase water destroyed the structure of DES and formed hydrogen bonds with hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA), respectively. Moreover, the hard sphere model was applied to study the viscosity, and after introducing the binary interaction parameter, the average absolute relative deviation of the mixture reduced to 4.4 ∼ 7.7 %.

Predicting the density and viscosity of deep eutectic solvents at atmospheric and elevated pressures

Deep eutectic solvents (DESs) are promising and sustainable substitutes for organic solvents in various applications. The knowledge of their density and viscosity at different temperatures and pressures is crucial for the corresponding process design. However, most literature primarily focuses on predicting these properties at atmospheric pressure. In this study, we employed the perturbed chain polar statistical associating fluid theory (PCP-SAFT) model and entropy scaling method to predict DESs’ density and viscosity at atmospheric and elevated pressures. 2831 density data points of 38 DESs and 1018 viscosity data points of 31 DESs at different temperatures and pressures were used to evaluate the accuracy of the applied methods. The pure component PCP-SAFT parameters of choline chloride (ChCl) were regressed using density data of ChCl-based DES at various temperatures and pressures. It was found that the PCP-SAFT model can provide satisfactory density predictions for DESs at atmospheric pressure, even without using the system-specific binary interaction parameter (kij=0). However, accurate viscosity prediction at atmospheric pressure for DESs necessitated the inclusion of the binary interaction parameter (kij=aijT+bij) in the PCP-SAFT model. The system-specific coefficients aij andbij, derived from experimental data at atmospheric pressure, were used to predict the density or viscosity of DES at elevated pressures. Accurate predictions for density were observed across the entire pressure range, whereas effective viscosity predictions were confined to a specific pressure range.

Accurate Machine Learning for Predicting the Viscosities of Deep Eutectic Solvents.

Deep eutectic solvents (DESs) are emerging as environmentally friendly designer solvents for mass transport and heat transfer processes in industrial applications; however, the lack of accurate tools to predict and thus control their viscosities under both a range of environmental factors and formulations hinders their general application. While DESs may serve as designer solvents, with nearly unlimited combinations, this unfortunately makes it experimentally infeasible to comprehensively measure the viscosities of all DESs of potential industrial interest. To assist in the design of DESs, we have developed several new machine learning (ML) models that accurately and rapidly predict the viscosities of a diverse group of DESs at different temperatures and molar ratios using, to date, one of the most comprehensive data sets containing the properties of over 670 DESs over a wide range of temperatures (278.15-385.25 K). Three ML models, including support vector regression (SVR), feed forward neural networks (FFNNs), and categorical boosting (CatBoost), were developed to predict DES viscosity as a function of temperature and molar ratio and contrasted with multilinear and two-factor polynomial regression baselines. Quantum chemistry-based, COSMO-RS-derived sigma profile (σ-profile) features were used as inputs for the ML models. The CatBoost model is excellent at externally predicting DES viscosity, as indicated by high R2 (0.99) and low root-mean-square-error (RMSE) and average absolute relative deviations (AARD) (5.22%) values for the testing data sets, and 98% of the data points lie within the 15% of AARD deviations. Furthermore, SHapley additive explanation (SHAP) analysis was employed to interpret the ML results and rationalize the viscosity predictions. The result is an ML approach that accurately predicts viscosity and will aid in accelerating the design of appropriate DESs for industrial applications.

Density and viscosity of deep eutectic solvents at different temperatures and compositions: Measurement and prediction model

AbstractDeep eutectic solvents (DESs) are becoming increasingly promising as environmentally friendly solvents, and accurate prediction of their density and viscosity is crucial for their successful industrial application. However, existing density and viscosity prediction models primarily rely on temperature variations and often overlook changes in the molar ratio of hydrogen bond acceptors (HBA) to hydrogen bond donors (HBD) in DESs, limiting their practicality. Therefore, in this study, several binary and ternary DESs were synthesized using choline chloride (ChCl) as the hydrogen bond donor. The densities and viscosities of these DESs were measured, and prediction models for the density and viscosity of DESs based on temperature and molar ratio were developed. These models were used to forecast the density and viscosity of DESs at different temperatures and molar ratios. The model parameters are calibrated using experimental data from this research. Finally, the model is utilized to predict the density and viscosity of DESs mentioned in this paper, as well as DESs with varying HBAs and HBDs. The results demonstrate that the discrepancy between the literature value, experimental value, and calculated value is less than 6%, confirming the universal applicability and reliability of the prediction model proposed in this study.

A comparative study of thermophysical properties between choline chloride-based deep eutectic solvents and imidazolium-based ionic liquids

In respond to the queries of deep eutectic solvent (DES) as a better analogue over ionic liquid (IL), this research aims in contributing a comparative study on the thermophysical properties of choline chloride-based DESs and imidazolium-based ILs to provide a general understanding on the similarities and differences of their properties. The thermal conductivity, viscosity and ionic conductivity of choline chloride-based DESs with glycerol (Gly) and ethylene glycol (EG) as hydrogen bond donors (HBDs) are characterized and compared with those of 1-ethyl-3-methylimidazolium chloride (EmimCl) and 1-hexyl-3-methylimidazolium chloride (HmimCl). It is observed that the thermal conductivity of DESs increases with salt: HBD molar ratio while that of ILs increases with alkyl chain length. Meanwhile, the viscosity of DESs is depending on the nature of HBD. DESs with glycerol as HBD show an incremental trend in viscosity with increasing molar ratio, while DESs with ethylene glycol as HBD depict an opposite trend. For ILs, longer alkyl chain length results in greater viscosity. The ionic conductivity of both DESs and ILs increase as their viscosity decrease. The effect of temperature is insignificant on the thermal conductivity of DESs and ILs. The viscosity of both DESs and ILs is reduced while their ionic conductivity is enhanced with increase of temperatures. When aqueous form of DESs and ILs is considered, water has greatly enhanced the thermal conductivity and ionic conductivity of DESs and ILs. However, the viscosity of DESs and ILs is drastically reduced with the presence of water content. In general, the thermophysical properties of both DESs and ILs are comparable, including in their aqueous forms. A prefeasibility study is conducted to further evaluate the potential and practicality of DESs and ILs in comparison with the conventional lubricant and battery electrolyte.

Comprehensive thermodynamic modeling framework for the estimation of physico-chemical properties of deep eutectic solvent-heavy crude oil system

Physico-chemical properties such as density, solubility parameter, viscosity, volume change on mixing and surface tension for pure deep eutectic solvent (DES), heavy crude oil (saturate, aromatic, resin and asphaltene i.e. SARA) and DES-SARA mixtures are estimated. The models are established considering the variation of SARA from three geographic locations and five DESs from hydrophilic and hydrophobic nature. Further, variation in temperature and concentration of DESs or SARA are explicitly considered. The structural variations are incorporated by estimating the critical properties in Lydersen–Joback–Reid framework using group contribution methodology. Cohesion based equation of state is used to estimate the density of SARA and DES. Geometric similitude concept in conjunction with cubic equation of state is used to estimate the surface tension and viscosity of DES and SARA. Later six different formulations namely, Arrhenius, Power law model, Lobe, Cragoe, Double-log, and Lederer model are employed to calculate the mixture viscosity of DES-SARA system.

In-depth theoretical study on the structures of betaine-1,2-propanediol based deep eutectic solvents

Deep eutectic solvents (DESs) have been arousing more and more attention because they meet the important standard of new green solvents, and have been widely used in chemistry. However, the further commercialization is limited by the inherent structural instability and high viscosity. An in-depth understanding of the atomic-level structure and the interactions between hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD) is conducive to better exploring the stability and properties of DESs. In this work, density functional theory (DFT) and molecular dynamics (MD) simulation were used to study the structure and properties of DESs synthesized by betaine and 1,2-propanediol with different molar ratios (1:3 to 1:6). It is confirmed that the relationship between betaine and 1,2-propanediol is essential for the formation of DESs with a reasonable number of hydrogen bonds. In-depth analysis of these hydrogen bonds based on the quantum theory of atoms in molecules shows that they belong to “weak to medium” category. It is mainly the electrostatic interaction between the oxygen atoms of betaine and hydrogen atoms from hydroxyl groups of 1,2-propanediol. In addition, the simulation results showed that the increase of 1,2-propanediol content weakens the hydrogen bond between betaine and 1,2-propanediol, and strengthens the hydrogen bond between 1,2-propanediol molecules. The viscosity of DESs is mainly dependent on the interaction between betaine and 1,2-propanediol. The changes in intramolecular interactions of DESs illustrate that HBD molecules such as 1,2-propanediol play a critical role in the development of application-specific DESs.

Efficient whole-cell biosynthesis of (S)-2-chloro-1-(3,4-difluorophenyl)-ethanol from 2-chloro-1-(3,4-difluorophenyl) ethanone in a sustainable reaction system

(S)-2-Chloro-1-(3,4-difluorophenyl)-ethanol [(S)-CFPL] is a key chiral intermediate in the manufacture of Ticagrelor. In this study, deep eutectic solvent (DES) was used as the co-solvent, and several reaction parameters were investigated and characterized. It was observed that supplementary of DES could promote the asymmetric reduction of 2‑chloro-1-(3,4-difluorophenyl) ethanone (CFPO) to (S)-CFPL through the biological reduction by recombinant E. coli containing a NADH-dependent reductase CmCR. The high pKa value of carboxylic acid in DES and low viscosity of DES were beneficial to increase cell membrane permeability and enhancement of biocatalytic efficiency. By supplementary of DES ChCl:LA (7.5 vol%) into the bioreaction system, the efficient bioreduction reaction of 100 mM CFPO was achieved via the biocatalysis with whole-cell at 30 °C and pH 7.0, affording (S)-CFPL in 95.9 % yield and optical purity > 99 %. The process was environmentally friendly with high biocatalytic productivity and had potential practicability in the mass production of (S)-CFPL.

Deep Eutectic Solvents Based on L-Arginine and 2-Hydroxypropyl-β-Cyclodextrin for Drug Carrier and Penetration Enhancement.

By selecting L-arginine as the hydrogen bond acceptor (HBA) and 2-hydroxypropyl-β-cyclodextrin (2HPβCD) as the hydrogen bond donor (HBD), deep eutectic solvents (DESs) with various water content were prepared at the 4:1 mass ratio of L-arginine to 2HPβCD with 40 to 60% of water, and were studied for its application in transdermal drug delivery system (TDDS). The hydrogen bond networks and internal chemistry structures of the DESs were measured by attenuated total reflection Fourier transform infrared (ATR-FTIR) and 1H-nuclear magnetic resonance spectroscopy (1H-NMR), which demonstrated the successful synthesis of DESs. The viscosity of DES was decreased from 10,324.9 to 3219.6mPas, while glass transition temperature (Tg) of the DESs was increased from - 60.8 to - 51.4°C, as the added water was increased from 45 to 60%. The solubility of ibuprofen, norfloxacin, and nateglinide in DES with 45% of water were increased by 79.3, 44.1, and 3.2 times higher than that in water, respectively. The vitro study of transdermal absorption of lidocaine in DESs showed that the cumulative amounts of lidocaine reached 252.4µg/cm2, 226.1µg/cm2, and 286.1µg/cm2 at 8h for DESs with 45%, 50%, and 60% of water, respectively. The permeation mechanism of DES with lower content of water (45%) was mainly by changing the fluidization of lipids, while changing the secondary structure of keratin in stratum corneum (SC) at higher water content (50% and 60%). These nonirritant and viscous fluid like DESs with good drug solubility and permeation enhancing effects have broad application prospect in the field of drug solubilization and transdermal drug delivery system.

Capillary electrophoresis instrumentation for determination of viscosity of deep eutectic solvents

Capillary electrophoresis instrumentation for determination of viscosity of deep eutectic solvents

Enhanced extraction of phenolic compounds from mango by-products using deep eutectic solvents

Deep eutectic solvents (DESs) potential for the extraction of polyphenolic compounds (PC) from mango by-products (peel and seed) was evaluated. Ultrasound (US) and agitation were applied to evaluate the effects of solvent and extraction methodology. The extracts were characterized with antioxidant capacity and HPLC-DAD profile. A theoretical study was performed using density functional theory and the QTAIM approach. β-alanine and choline chloride based DESs were effective to extract PC from peel and seed. Some DES increased PC extraction up to three times for peel (23.05 ± 1.22 mg/g DW) and up to five time for seeds (60.01 ± 1.40 mg/g DW). The PC profile varied with the solvent (DES vs EtOH/MeOH), procedure (US vs agitation) and material (peel or seed). Mangiferin extraction from peels was significantly increased with β-alanine based DES (676.08 ± 20.34 μg/gDW). The strength of H-bonds had a determining effect on the viscosity of DESs. The solute-solvent solvation energy was suitable to estimate the strength of H-bond interactions between DES and target compounds. This study demonstrates the remarkable capacity of DESs to extract PC from mango by-products and provides insights into the factors controlling extraction properties.

Entropy scaled viscosities of choline-chloride-based deep eutectic solvents using a cubic EoS with volume translation

The present modeling work formally introduces, for the very first time, the application of the residual-entropy scaling approach to adequately represent the dynamic viscosity of deep eutectic solvents (DESs) as a function of temperature and density. In doing so, diverse unreduced and reduced viscosity forms (total viscosity, Rosenfeld and dilute gas) were verified and compared. The use of a cubic equation of state (CEoS: Soave-Redlich-Kwong or Peng-Robinson) served here to provide sufficiently accurate residual entropy data required by the present scaling procedure. Experimental DES density data were also modeled by applying a modified Mathias volume translation to the density data originally obtained from the two CEoS during the present scalings. The resulting modeling approach was sucessfully validated during the representation of experimental dynamic viscosities and mass densities of three of the most representative choline chloride-based DESs: ChCl:Urea(1:2), ChCl:Ethylene Glycol(1:2) and ChCl:Glycerol(1:2) within a temperature range varying from 10 to 100 °C and at pressures from 1 to 1,000 bar.

Absorption of dichloromethane in deep eutectic solvents: Experimental and computational thermodynamics

A series of benzyl-based deep eutectic solvents (DESs) were successfully prepared and used for the capture of condensable dichloromethane gas. The COSMO-RS model was implemented to screen out the appropriate absorbent (i.e., DES TEBAC-TEG) for capturing dichloromethane. The physical properties of density and viscosity of DESs were measured to prove the feasibility of industrial application. The result of absorption experiment shows that TEBAC-TEG (the molar ratio 1:3) has big capacity of 581.72 mg/g with DCM partial pressure of 50 kPa at 303.15 K, and the removal ratio of dichloromethane reached 91.65 %. Further, the absorption mechanism was revealed by Gibbs free energy analysis and quantum chemical calculations. It was found that both chloride ion and TEG displayed high hydrogen bond (HB) acceptance ability, which could form HB with dichloromethane to enhance the absorption process. Particularly, the CH⋅⋅⋅π interaction is dominant between TEBA cation and dichloromethane molecule.

Comparison of polyol-based deep eutectic solvents (DESs) on pretreatment of moso bamboo (Phyllostachys pubescens) for enzymatic hydrolysis

Four polyol-based deep eutectic solvents (DESs) were designed for bamboo pretreatment and enzymatic hydrolysis , and the pretreatment conditions including temperature, time and acid dosage in the optimized DES were comprehensively evaluated. The results showed that the components separation and saccharification of bamboo could be promoted by polyol-based DESs pretreatment, which are positively correlated with the hydroxyl contents of hydrogen bond donor in DESs, except for sorbitol-based DES. Excessive hydroxyl contents could lead to the increase of DES viscosity and lignin deposition, which had a negative effect on saccharification. Meanwhile, the optimum pretreatment conditions in xylitol-based DES (ChCl/XL) were determined to be 120 °C for 3 h with 1wt% acid, and 96.08% of glucose yield was recorded. The recycling experiment indicated that ChCl/XL retained acceptable pretreatment performance. This work gives novel insights into the design and selection of polyol-based DES for bamboo pretreatment and enzymatic hydrolysis. • A novel insights into polyol DES pretreatment was designed for enzymatic hydrolysis. • The optimum pretreatment solvent is xylitol-based DES (ChCl/XL). • ChCl/XL can be adjusted by adding acid to keep its capability after multiple cycles. • Glucose yield was 96.08% at the optimal condition (120 °C, 3 h, 1wt% acid).

Understanding the side chain effect on regulation of CO2 capture by amino acid-based deep eutectic solvents

CO2 capture from post-combustion is essential for reducing CO2 emission and further turning waste CO2 into marketable industrial and commercial products. Herein, in this study, the effect of side chain on the CO2 absorption by deep eutectic solvents (DES) based on amino acid (AA) and monoethanolamine (MEA) was examined. The presence of functional group in AAs leads to an increase in the DES viscosity and a reduction in the reaction rate of DESs with CO2, further resulting in a decrease in the CO2 absorption in the order of –OH < –SH < –COOH < –CONH2. Moreover, the effect of the number of alkyl group on the activation energy barrier is associated with the functional group types. Experimental and DFT results reveal that in the initial absorption stage the CO2 absorption is mainly mediated by the reaction rate of DES with CO2, while with the absorption time increasing, the mass transfer rate becomes a predominant role due to a significant elevation in the viscosity caused by the carbamate formation. This study paves a way for DES development for CO2 capture.

CO2 absorption performance of ChCl-MEA deep eutectic solvent in microchannel

Deep eutectic solvent (DES) has been a new type of absorbent for CO2 capture due to the advantages of environmental friendliness, simple synthesis and excellent selectivity. A series of choline chloride (ChCl)-monoethanolamine (MEA) deep eutectic solvents with various water contents were prepared. The effects of gas-liquid flow rate, molar ratio of ChCl-MEA, water content and temperature on CO2 absorption performance and mass transfer were investigated. The addition of an appropriate amount of water can effectively reduce the viscosity of DES and improve its CO2 capture ability. The results show that the CO2 absorption efficiency, absorption rate, loading and mass transfer coefficient of ChCl-MEA deep eutectic solvent are optimal when the water content is 70 wt% for the DES with the molar ratio of ChCl and MEA 1:6. When the water content exceeds 70 wt%, the hydrogen bond network of DES would be destroyed, and its CO2 capture ability would be weakened. According to the Arrhenius equation, the reaction activation energy of CO2 absorption is as low as 7.54 kJ·mol−1 when the water content is 70 wt% in DES with the molar ratio of ChCl and MEA 1:6. This study can provide technical support for the application of deep eutectic solvents in CO2 capture.

Density, Viscosity, and Refractive Index of a Choline Chloride + d-(−)-Fructose Deep Eutectic Solvent + Water Mixture at Different Temperatures: An Experimental Study and Thermodynamic Modeling

In the present study, first, the deep eutectic solvent (DES) of choline chloride + d-(−)-fructose was prepared using the heating method. Then, its physical properties including density, viscosity, and refractive index were experimentally measured at temperatures in the range of 283.15–343.15 K and a full composition range of DES at atmospheric pressure (83.09 kPa). The values of these three properties decrease with an increase in temperature, while the mole fraction has a nonlinear effect on these properties. For the density and refractive index, an increase in the mole fraction of DES to 0.3 causes a sharp increase in these physical properties, while from 0.3 to 1, this increase occurs slowly. For viscosity, increasing the mole fraction of DES has little effect at first, but at high mole fractions of DES, a sharp increase in viscosity occurs. In addition, the sharp change in the viscosity of DES depends on the temperature so that at low temperatures, this phenomenon occurs faster. So, adding water to DES will tailor the viscosity of the mixture to facilitate its applications. A polynomial equation was used to describe the density and refractive index as a function of temperature and mole fraction. Experimental viscosity was fitted to the Vogel–Tammann–Fulcher (VTF) equation. Using the measured data, in sequence, the values of excess molar volume (VmEx), viscosity deviation (Δη), and refractive index deviation (ΔnD) were calculated. The Redlich–Kister polynomial equation, finally, was used to correlate the values of VmEx, Δη, and ΔnD.

Oxidation-extraction desulfurization of fuel with a novel green acidic deep eutectic solvent system

Deep eutectic solvents (DESs) have important application prospects in fuel desulfurization. A novel dual Brønsted acidic DES was proposed and successfully synthesized for one-pot oxidation-extraction desulfurization process, in which a green and harmless choline chloride (ChCl) was used as hydrogen bond acceptor, p-toluenesulfonic acid (TsOH) and oxalic acid (OA) were used as hydrogen bond donors to provide acidic groups. The results showed that the new DESs (ChCl/2TsOH/0.2OA) had the excellent desulfurization efficiency due to the strong acidity based on the synergistic effect between the two acidic groups. The content of benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) could be reduced to 8.82 ppm (120 min), 1.23 ppm (90 min), and 7.75 ppm (90 min), respectively. Electron spin resonance and radical capture experiments showed that superoxide radicals (·O2–) were the main oxidizing agents. The possible oxidation-extraction pathway was that DBT was extracted from oil phase into DES phase, and the DES was converted to peroxy acid in the presence of ·O2–, then the extracted DBT in DES phase was oxidized to high polar sulfone. It can be regenerated and recycled by simple water washing. To improve dispersion and treatment efficiency, reduce the amount of DESs, the viscosity of DESs was adjusted by using sulfolane as the dilute, which could significantly reduce the operation time and enhance the desulfurization effect. The content of BT, DBT, and 4,6-DMDBT could be reduced to 12.20, 2.21, 7.38 ppm only need 45, 5, and 15 min, correspondingly. The novel green DES can provide theoretical support and technical guidance for deep fuel desulfurization.

Effect of hydration on intermolecular interactions in tetrabutylammonium chloride based deep eutectic solvents

The high viscosity of deep eutectic solvents (DESs) restricts their applications in various fields, which can be overcome by the addition of water. The knowledge of the new interactions arising between the components of DES and water in their mixtures is important for the understanding of the changes in their liquid structures. Molecular dynamics simulations have been carried out on two hydrated DESs based on tetrabutylammonium chloride at three different concentrations, to gain atomic-level insights into the structural changes. Intermolecular interactions in the DESs are influenced by the addition of water due to the preferential solvation of anions. Water forms hydrogen bonds with DES components and has the most significant interaction with the anion, which is evident from the radial and spatial distribution functions. Mean squared displacements and self-diffusion coefficients of the components of the DES increase with the hydration level due to the decrease in the interactions between the constituents of DES. The reduction in the intensity of the peak in structure factor also signifies the effect of water on long-range interactions.

Study on the technology of efficient extraction of eleutheroside E from Acanthopanax senticosus by green solvent DES.

Acanthopanax senticosus (Rupr. & Maxim.) Harms is a medicinal and edible plant which is clinically used for the recovery and treatment of cardiovascular and central diseases. As a characteristic active pharmaceutical ingredient of Acanthopanax senticosus, eleutheroside E is the core of the therapeutic effect. Organic solvent extraction has low selectivity, low extraction rate, difficulty in separation and purification and safety risks. The purpose of this study was to extract the effective component of Acanthopanax senticosus with a new green solvent. In this article, two kinds of deep eutectic solvents (DESs) (DES-1 and DES-2) were synthesised by heating and stirring methods. Eleutheroside E was extracted by ultrasonic extraction with two kinds of DES as extractants and quantitatively analysed by Orbitrap-tandem mass spectrometry (MS/MS). The main results showed that the initial polarity of the DES was similar to that of 60 to 80% ethanol and hydrogen bond donors were the main factors affecting the polarity of DES. In the test, the viscosity of DES was higher than that of ethanol, and even the addition of a small amount of water (10%) caused intermolecular hydrogen bond disruption and redistribution of the solvent, resulting in a significant decrease in solvent viscosity. The solvents in the test group were stable after standing at 5°C in the dark for 100 days. The extraction rate of eleutheroside E by DES solvent was 5-6 times higher than that by ethanol. DES-1 and DES-2 can efficiently extract eleutheroside E. This study developed a new method for the application of the green extraction of eleutheroside E with certain practical significance.