Hydrophobic Deep Eutectic Solvents Research Articles

An eco-friendly and high-yield extraction of rare earth from the leaching solution of ion adsorbed minerals

Ion-adsorbed rare earth minerals are rich in medium and heavy rare earth (RE), which are important strategic resources. In this article, a novel approach for the extraction of RE from ion adsorbed minerals was developed. Through a comprehensive assessment of their extraction and separation performance, the hydrophobic deep eutectic solvents (HDES) with a composition of trioctylphosphine oxide (TOPO): dodecanol (LA): 2-thiophenoyltrifluoroacetone (HTTA) = 1:1:1 was determined as the optimal configuration. Under optimized conditions, only RE were extracted by the HDES, while Al, Ca, Mg were not extracted at all. The HDES based extraction obviated the need for diluent such as kerosene, eliminating the generation of impurity removal residues. The RE in the stripping solution could be successfully enriched by saponified lauric acid, achieving an impressive precipitation rate of 99.7%. The RE precipitate underwent further enrichment, resulting in a RE concentration of 176 g/L (REO = 210 g/L). Unlike industrial precipitants such as oxalic acid and ammonium bicarbonate, lauric acid can be effectively recycled, thereby avoiding a large amount of wastewater and carbon dioxide emissions. The obtained RE solution product exhibits high yield and purity, this study provides an eco-friendly and high-yield approach for extracting RE.

Hydrophobic deep eutectic solvent-based vortex-assisted dispersive liquid–liquid microextraction with UV–visible spectrophotometry for copper determination in waste printed circuit boards

ABSTRACT Nearly all electronic devices utilise Printed Circuit Boards (PCBs), which contribute significantly to the generation of electronic waste (e-waste). They are rich in metal content, with copper being present in higher percentages. In this work, a simple, efficient and environment-friendly pre-concentration technique was developed, using hydrophobic deep eutectic solvent as an extractant in vortex-assisted dispersive liquid–liquid microextraction. This pre-concentration technique is coupled with spectrophotometry for the determination of copper in PCBs. The complexing agent, sodium diethyl di-thiocarbamate (DDTC), and copper formed a complex in the 2–3 pH range. The Cu-DDTC complex was vortexed for 1 min at 2800 rpm to extract in hydrophobic DES. The sediment was analysed using a UV–Visible spectrophotometer at λ max 435 nm. The optimisation parameters, including pH, extraction solvent selection and its volume, concentration and volume of chelating agent, interference of forein ios, etc., have been assessed. Analytical figures of merit such as limit of detection (1.98 μg/L), limit of quantification (5.9 μg/L), relative standard deviation (3.4%) and enrichment factor (10) have been obtained under optimal experimental conditions. The method was validated by a certified copper solution and applied successfully to determine copper in waste PCBs of personal computers.

Feasibility of Different Methods for Separating n-Hexane and Ethanol

Conventional distillation methods cannot effectively separate the components of an azeotropic mixture since both phases have the same composition, thereby preventing further separation. Additional techniques such as pressure swing distillation or distillation with entrainers are often employed to overcome this limitation and achieve separation. The aim of this investigation was to select the most effective method for separating n-hexane and ethanol. The feasibility of three methods was analyzed: reduced pressure distillation, extractive distillation, and liquid–liquid extraction. The mutual solubility of n-hexane and prepared deep eutectic solvents (DESs) (nine hydrophilic: choline chloride with glycerol, ethylene glycol, or carboxylic acid (malic, citric, glycolic); tetramethylammonium chloride with glycolic acid; lactic acid with glycerol; K2CO3 with glycerol or ethylene glycol; two hydrophobic: menthol with decanoic or dodecanoic acid) was experimentally determined. Extraction experiments were conducted to test the solubility of DESs in the feed mixture. The effect of changing DES-to-feed mass ratio was further investigated with choline chloride–glycerol (1:2). The same DES and both hydrophobic DESs were able to increase the relative volatility and enhance the separation of ethanol and n-hexane. Based on the obtained results, extraction was selected as the most effective method for the separation of n-hexane and ethanol.

Platinum Group Metal Recycling from Spent Automotive Catalysts Using Reusable Hydrophobic Deep Eutectic Solvent

Platinum Group Metal Recycling from Spent Automotive Catalysts Using Reusable Hydrophobic Deep Eutectic Solvent

Fast and efficient extraction of phenol from aqueous phase using deep eutectic solvents: Experimental and density functional theory investigation for interactions studies

Phenol is carcinogenic and toxic to human beings and therefore it is necessary to remove this toxic pollutant from water. Hydrophobic deep eutectic solvents (DESs) were prepared using trioctylamine (TOA) as hydrogen bond acceptor (HBA) and 2-hydroxybenzoic acid and 4-dodecylbenzenesulfonic acid as hydrogen bond donors (HBDs) for extraction of phenol from aqueous media. Fourier transformer infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) were performed for functional group and thermal stability determination, respectively. Phenol extraction efficiency of DESs was studied under different experimental parameters, such as initial pH of phenol solution (2–10), contact time (1–15 min), mixing ratio of volume of DESs to aqueous media (VDES:Vaq.) (1:10–1:50 mL), initial concentration of phenol (1000–5000 ppm) and temperature (25 °C–55 °C). More than 97 % extraction efficiency of DES for phenol was achieved using contact time of 5 min, initial phenol concentration of 2500 ppm, VDES:Vaq in a ratio of 1:10 mL, and temperature of 25 °C. The values of ΔG° calculated for phenol extraction at various temperatures have negative values, confirming that the phenol movement from water phase to DESs phase is spontaneous in nature. Density functional theory (DFT) simulations were conducted to study the interaction of DESs with water and phenol. In addition, DFT was used to determine the interaction energy of DESs with water and phenol. The considerably higher interaction energies (−20.4 and 18.2 kcal/mol) obtained with both DESs for phenol over water emphasize the selective separation efficiency of DESs for phenol. The experimental results confirmed that these synthesised DESs can effectively extract phenol from the aqueous phase to the organic phase.

Reactive liquid-liquid extraction of lactic acid from microfiltered sweet sorghum silage press juice in an agitated extraction column using a hydrophobic natural deep eutectic solvent as modifier

Downstream processing of carboxylic acids from fermentation broths is cost-intensive and environmentally harmful, which makes methods such as reactive liquid-liquid extraction attractive separation technologies. To enhance the sustainability of liquid-liquid extraction processes, research focuses on sustainable solvents like hydrophobic natural deep eutectic solvents. However, the application of hydrophobic natural deep eutectic solvents in agitated extraction columns for continuous processing has never been investigated. This is essential to facilitate their use in industrial processes, promoting cleaner production. In this study, the application of a thymol-menthol-based deep eutectic solvent as a modifier (with the extractant tri-n-octylamine) in an agitated extraction column is evaluated for reactive liquid-liquid extraction of lactic acid from microfiltered sweet sorghum silage press juice. In addition, three-stage cross-current extractions were performed. The thymol-menthol-based deep eutectic solvent showed efficient phase separation, stable operation, and chemical stability in the agitated extraction column. In three-step cross-current operation, the extraction efficiency for lactic acid was increased from 37.0 ± 0.4 % without feed pH adjustment to 76.2 ± 0.9 % with continuously adjusting the pH value to 2.05 ± 0.02. The thymol-menthol-based deep eutectic solvent shows great potential for application in agitated extraction columns. This is highly promising because natural deep eutectic solvents can enhance the sustainability of extraction processes and reduce the reliance on fossil-based solvents.

Study of the experimental and microscopic mechanism of the removal of phenolic compounds from wastewater based on hydrophobic deep eutectic solvents

Dephenolisation has been a key environmental concern; therefore, separating and recycling phenolic compounds from wastewater can reduce environmental harm and the consumption of resources, respectively. Herein, we selected three hydrogen bond acceptors (HBAs) and three hydrogen bond donors (HBDs) with excellent industrial prospects, which were widely sourced, and combined them as nine hydrophobic deep eutectic solvents (HDESs) to perform liquid–liquid extraction (LLE) experiments and molecular simulation studies on model wastewaters containing phenol and catechol. The preliminary screening of HDESs was carried out by conducted with quantum chemical simulations using σ-Profiles, and the microscopic mechanism of the extraction process using HDESs was analysed through molecular dynamics (MD) simulations based on radial distribution function, spatial distribution function, mean square displacement and interaction energy results. Guided by the above molecular simulation results, experimental studies on LLE using HDESs were further conducted to determine the optimal conditions of the experimental operation, including the types and ratios of HBAs and HBDs, feed ratios between the HDESs and model wastewater, and extraction temperatures. The experimental studies revealed that the extraction efficiency of octanoic acid − geraniol (molar ratio 1:3) on a 0.6 % (mass concentration) phenol and catechol model wastewater at 25℃ could reach > 96 %. Moreover, the results were consistent with that of MD simulation. The above methodologies provide a reliable basis for resolving similar problems.

Rapid synergistic cloud point extraction based on hydrophobic deep eutectic solvent combined with hydride generation atomic absorption spectrometry for determination of selenium in tea samples

Herein, hydrophobic deep eutectic solvents (HDESs) were created for the fast preconcentration of Se(IV) from tea samples at room temperature. A facile and rapid synergistic cloud point extraction (HDES-RS-CPE) procedure was used, followed by hydride generation atomic absorption spectrometry (HG-AAS). The selected synergistic DES included glycine and lauric acid (molar ratio 3:1). 2-hydroxy-5-p-tolylazobenzaldehyde (HTAB) and Triton X-114 were utilized as chelating reagent and non-ionic surfactant, respectively. The experimental parameters that impact extraction recovery were examined and optimized. The detection limit, quantification limit, preconcentration factor, and enhancement factor for Se(IV) under optimum circumstances were 0.02 μg L−1, 0.06 μg L−1, 125, and 149, respectively. The method exhibited analytical linearity in the range up to 700.0 μg L−1. The procedure was used effectively for the quantification of Se(IV) in tea and certified samples. Moreover, the National Environmental Method Index (NEMI), the analytical greenness scale for sample preparation (AGREEprep), and the Green Analytical Procedure Index (GAPI) criteria have been used to measure the greenness score of the extraction procedure. To further highlight the environmental friendliness of this method, a detailed evaluation has been performed.

Developing of an eco-friendly liquid-liquid microextraction method by using menthol-based hydrophobic deep eutectic solvent for determination of basic fuchsin dye: assessment of the greenness profile.

Herein, we aimed to develop a new environmentally friendly liquid-liquid microextraction (LLME) method based on hydrophobic deep eutectic solvent (hDES) synthesized using biodegradable dl-menthol and decanoic acid for the spectrophotometric determination of toxic basic fuchsin dye in environmental water samples. The parameters affecting the extraction efficiency such as pH, mole ratio, and volume of hDES (1:2) and type and volume of organic solvent, sample volume, times of vortex, ultrasonic bath and centrifuge, ionic strength, and matrix effect were investigated and optimized. Under optimal conditions, the calibration curve showed linearity in the range of 7.4-167μg L-1 with a coefficient of determination of 0.9994. The limit of detection, intra-day and inter-day precision, and recovery values were 2.25μg L-1, 2.46% and 4.45%, and 105 ± 3%, respectively. The preconcentration and enrichment factors were found to be 30 and 61.5, respectively. The proposed hDES-LLME methodology was successfully applied to the environmental water samples to detect toxic BF dye (95-105%). Finally, the ecological impact of the suggested method was evaluated using the analytical eco-scale (PPS:88), complementary green analytical procedure indexe (ComplexGAPI), and the Analytical GREEnness tool (0.63). The assessment results showed that the presented analytical method can be regarded as a green LLME approach for the determination of the BF in water.

Experimental and mechanism study on the separation of isobutyl alcohol and water azeotrope using hydrophobic deep eutectic solvents

Isobutyl alcohol with good miscibility, high octane number and energy density has been paid more and more attention in the field of new biofuels, as it is an ideal alternative fuel for gasoline. However, isobutyl alcohol and water azeotrope need a clean and efficient separation method to realize the separation in isobutyl alcohol production process and industrial wastewater. Three hydrophobic deep eutectic solvents (DESs) were used to separate isobutyl alcohol. Decanoic acid was used as hydrogen bond donor and menthol, thymol and lidocaine were used as hydrogen bond acceptors to synthesize DESs. The liquid-liquid equilibrium experiment was carried out for the system containing DESs and MSD −water at 101.3 kPa and 303.15 K, and the separation effect of different DESs was indicated using distribution coefficient (β) and selectivity (S). The σ-Profile can be a good reflection of the strength of a substance's ability to accept and provide hydrogen bonds. The interaction energy and self-diffusion coefficient of the separation system were described quantitatively by molecular dynamics simulation. The relationship between DESs and the separation system was analyzed quantitatively by radial distribution function and spatial distribution function. The separation results show that the three DESs have good separation effect on isobutyl alcohol-water system, among which the DESs synthesized by thymol and decanoic acid has the best separation effect, and the interaction of isobutyl alcohol-water separation process is controlled by van der Waals forces. DESs plays an important role in the separation and treatment of isobutyl alcohol-containing wastewater, and promotes the sustainable development of wastewater treatment projects to save costs and increase production benefits.

Anhydrous volatile fatty acid extraction through omniphobic membranes by hydrophobic deep eutectic solvents: Mechanistic understanding and future perspective

Volatile fatty acids (VFAs) derived from arrested anaerobic digestion (AD) can be recovered as a valuable commodity for value-added synthesis. However, separating VFAs from digestate with complex constituents and a high-water content is an energy-prohibitive process. This study developed an innovative technology to overcome this barrier by integrating deep eutectic solvents (DESs) with an omniphobic membrane into a membrane contactor for efficient extraction of anhydrous VFAs with low energy consumption. A kinetic model was developed to elucidate the mechanistic differences between this novel omniphobic membrane-enabled DES extraction and the previous hydrophobic membrane-enabled NaOH extraction. Experimental results and mechanistic modeling suggested that VFA extraction by the DES is a reversible adsorption process facilitating subsequent VFA separation via anhydrous distillation. High vapor pressure of shorter-chain VFAs and low Nernst distribution coefficients of longer-chain VFAs contributed to DES-driven extraction, which could enable continuous and in-situ recovery and conversion of VFAs from AD streams.

Dibutylamide hydrophobic deep eutectic solvent used for selective extraction of Au(III) from hydrochloric acid medium

The effective and environmentally friendly recovery of gold from secondary resources has recently received increased attention. Hydrophobic deep eutectic solvent (HDES) composed of N,N-di-butylacetamide and 1-decanoic acid was used to construct the liquid-liquid extraction system to extract Au(III) from HCl medium. At first, DSC, TGA, FT-IR, and 1H NMR were used to describe the evidence of internal hydrogen bond interaction. The above evidence was verified in the molecular dynamics study of HDES. Then, a series of optimization experiments were carried out to investigate the extraction behaviors of HDES. Based on the results of optimization experiments, response surface method was used to explore the best experimental conditions and the results showed that HDES extracted 99% Au(III) under 0.56 mol/L HCl, 2.19 mol/L NaCl, and 5.83 mmol/L Au(III), and the maximum loading reached 77.0 mg/g. Further studies on the kinetics and thermodynamics of the extraction were used to propose an ion association mechanism. In addition, using 0.1 mol/L thiourea as the stripping agent, HDES displayed outstanding Au(III) selectivity and maintained the extraction efficiency in tests which involved 5-cycles. Overall, this study provides a green and efficient Au(III) recovery strategy for secondary resources.

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 %.

Greener Route for Recovery of High-Purity Lanthanides from the Waste of Nickel Metal Hydride Battery Using a Hydrophobic Deep Eutectic Solvent

Greener Route for Recovery of High-Purity Lanthanides from the Waste of Nickel Metal Hydride Battery Using a Hydrophobic Deep Eutectic Solvent

Study of the intermolecular interaction in hydrophobic deep eutectic solvent of (2-n-octyl-4-isothiazolin-3-one + 1-decanol) from the density, viscosity, thermodynamic, spectroscopic and quantum chemical calculations

Hydrophobic deep eutectic solvents (HDESs) are considered as green solvents and have been developed rapidly in recent years, which are widely used in diverse applications. In this study, we introduce a binary system composed of 2-n-octyl-4-isothiazolin-3-one (OIT) as a novel hydrogen bond acceptor (HBA) and 1-decanol as a hydrogen bond donor (HBD) under atmospheric pressure. The fundamental physicochemical properties, including density and dynamic viscosity, of the binary systems with various mole ratios were measured at temperatures of 293.15 K, 303.15 K, 313.15 K, 323.15 K, and 333.15 K. The excess molar volume (VmE), viscosity deviation (Δη) and excess Gibbs free energy (ΔG∗E) for activation of viscous flow were calculated and fitted according to the Redlich-Kister type polynomial equation. Furthermore, the spectral analysis (FTIR, UV–vis and 1H NMR) confirmed the presence of intermolecular hydrogen bonding in the binary systems. In addition, quantum chemical calculations revealed that there may be multiple modes of hydrogen bond formation between OIT molecule and 1-decanol molecule. However, selecting the most energetically favorable point, the most prominent hydrogen bond was found to be between the amide O atom of OIT and the hydroxyl H atom of 1-decanol.

Removal of phenolic inhibitor compounds from hydrolysates and post-fermentation broths by using a hydrophobic magnetic deep eutectic solvent

Hydroxymethylfurfural (HMF), furfural (FF), hydroquinone (HQ), and vanillin (VAN) are among the main inhibitors generated during most of biomass pre-treatments prior to fermentation processes. They are recognized as toxic to several fermentative microorganisms and therefore cause a decrease in biohydrogen or biofuel production (after hydrolysis). Moreover, if they are released into aqueous solutions (after fermentation), they can be detrimental to the ecosystem. In this research, a new method for removing these inhibitor compounds from the broth after hydrolysis and fermentation is proposed. A hydrophobic magnetic deep eutectic solvent (HMDES), based on menthol: nonanoic acid in a mole ratio of 2:1 was prepared and magnetized with Fe3O4 nanoparticles and applied for effective sorption and removal of these inhibitors from the broth after fermentation and for biomass hydrolysates. Parameters affecting sorption, such as pH, volume of the inhibitors, initial concentration of inhibitors, volume of HMDES, temperature, stirring speed, and contact time, were studied and optimized. Under optimum conditions, the removal efficiency for HQ, HMF, FF, and VAN was obtained as 92.97, 86.72, 82.86 and 95.12% for the model samples. In addition, the removal efficiency of real samples after hydrolysis and fermentation for HQ, HMF, FF and VAN were higher than 83.3, 71.42, 69.99 and 76.80%, respectively. The studies on HMDES regeneration revealed that the removal efficiency remained constant even after undergoing 13 cycles of regeneration. The mechanism of inhibitor removal suggests that hydrogen bonding or van der Waals interactions may serve as the predominant factor influencing the extraction process.

Experiment and microscopic analysis for the separation of isopropanol‐water using hydrophobic deep eutectic solvents

AbstractIn this study, a method for separating isopropanol from wastewater using hydrophobic deep eutectic solvents (DESs) synthesized from terpenes and capric acid was proposed. The distribution coefficient and selectivity value of isopropanol (IPA) in the solvents were determined by liquid–liquid extraction experiments, and the extraction performances of the solvents at different molar ratios and temperatures were studied. From the perspective of molecular dynamics simulations, the experimental results were verified by mechanism analysis, the contribution of hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) to the selective separation of isopropanol was explained. The interaction energies, radial distribution functions, normal density distribution, and mean square deviations between the atoms were used to analyze the interactions between the components of the DESs and IPA/water. It was observed that the DESs have a good extraction effect on IPA, which verifies the good application prospects of DESs in wastewater solutions containing alcohol compounds.

Removal of Propylparaben in an Aqueous System using Magnetite-Silica Ferrofluids of Hydrophobic Deep Eutectic Solvent

A novel sorbent based on ferrofluid hydrophobic deep eutectic solvent magnetite silica (Fe3O4@SiO2@mSiO2- HDES) was successfully synthesized by adding menthol-fatty acid as carrier liquid onto Fe3O4@SiO2@mSiO2 composite. The crystallinity, morphological, functional group and magnetic properties of the materials were characterized by x-ray diffraction, scanning electron microscopy-EDX, Brunauer–Emmett–Teller, vibrating sample magnetometer, thermogravimetric analysis and Fourier Transform-infrared spectroscopy. The adsorption performance of parabens was evaluated as model water pollutants. The Fe3O4@SiO2@mSiO2-HDES ferrofluid was used as a ferrofluid sorbent of parabens prior to spectrophotometry UV-Vis. The effect of several contribution parameters was optimized including ferrofluid volume, pH, stirring time and ionic strength. Under the optimum conditions, a combination of Fe3O4@SiO2@mSiO2-menthol/palmitic acid was achieved as the best ferrofluid with % removal values ranging from 81.00% to 98.62%. The ferrofluid Fe3O4@SiO2@mSiO2-HDES demonstrated high efficiency for the adsorption paraben in the water system which suggests a great potential alternative method for the adsorption of water contaminants in the aquatic system.

Green recovery of platform chemicals from hydrothermal carbonization process water

This study explores the side-recovery of platform chemicals in the hydrothermal carbonization waste-to-energy chain. Up to 90 % of target chemicals, furfural and 5-hydroxymethylfurfural, were green extracted from the process waters using the hydrophobic deep eutectic solvent decanoic acid/thymol. Wheat straw and rice husk reacted (1/4 solid/water ratio) for up to 120 min and at 180 and 230 °C. The dissolved chemicals built up to 5.9 g/L, accounting for 12 % of the total carbon. Extractions from the process waters and those from reference solutions behaved similarly. The solvent affinity toward furfural is 3.5 times higher than that of 5-hydroxymethylfurfural. The aqueous raffinates chromatographic outline demonstrated the recyclability for prosecuting the HTC. Focused experiments mimicked the functioning of an industrial cascade of two crosscurrent mixer settlers. Extraction yields were 90.7 and 65.8 % for furfural and 5-hydroxymethylfurfural. The counterflow arrangement, simulated by the Kremser method, gave corresponding higher yields, 96.9 and 73.4 %, respectively.

Simultaneous and selective extraction of different polarity bioactive substances from Ligustri Lucidi Fructus based on a designable biphasic deep eutectic solvent

Most plants contain hydrophilic and hydrophobic bioactive compounds, traditional organic solvent extraction processes can often only extract one of the components, resulting in a cumbersome process and a waste of resources. To make full use of the active resources in Ligustri Lucidi Fructus, a biphasic deep eutectic solvent (DES) system was established. By adjusting the polarity, oleanolic acid (OA) and ursolic acid (UA) were enriched in the hydrophobic phase, and flavonoids and procyanidine (PAC) in the hydrophilic phase, respectively. Established with a 1:1 vol ratio of hydrophobic DES MIA (DL-menthol: isopropyl alcohol, 1:1) and hydrophilic DES CBE (choline chloride: betaine: ethylene glycol, 1:1:2). The biphasic system had the highest extraction rate. The response surface method was used to further optimize the extraction conditions. After optimization, the extraction yields of OA and UA were 10.96 ± 0.35 mg/g and 11.67 ± 0.26 mg/g in the MIA phase, and the extracted yields of flavonoids and PAC in the CBE phase were 77.38 ± 0.62 mg/g and 5.20 ± 0.03 mg/g, respectively. Compared with the conventional single-phase extraction with organic solvents, the biphasic system provided higher extraction rate and selectivity and the extracts showed stronger antioxidant activity. Compared to the single-phase extraction utilizing conventional organic solvents, the results demonstrated significant improvement. Consequently, by adjusting the polarity of the biphasic DES system, this study supplies an argument for increasing the extraction efficiency of plant resources. This expands the application of the biphasic DES system and contributes to the high-value exploitation of natural commodities.