Hydrophobic Eutectic Solvents Research Articles

New family of Type V eutectic solvents based on 1,10-phenanthroline and their application in metal extraction

Although a theoretically extensive number of hydrophobic eutectic mixtures suitable for solvent extraction are obtainable, to date reported mixtures rely on a limited number of chelating groups, namely phosphine oxide, carboxylic acid, and ketones. Herein, a new family of Type V Deep Eutectic Solvents (DES) based on the polypyridyl ligand 1,10-phenanthroline (phen) is presented with the aim of facilitating the extrapolation of the disclosed findings to other potential systems based on phen or bipyridine derivatives. The hydrophobic eutectic solvent composed of the natural phenolic extract thymol with phen exhibits a solid-liquid phase diagram with a useable liquidus compositional range on the thymol-rich side. The physical properties of the mixture are dependent on the presence of solutes liable to change the nature of the existing hydrogen-bonded network, most notably through the protonation of phen. The metal chelating ability of phen are retained when included as a DES component. Quantitative extraction of various transition metals cations (Cd(II), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)) as well as the platinum group metal Pd(II) was obtained across a range of solvent compositions. The extraction of Li(I), Mn(II), Co(II) and Ni(II) was further studied as a function of the aqueous phase pH, with the extent of metal partition decreasing with the protonation of phen at pH values below 1.0. Building upon the luminescent properties of phen, the eutectic solvent was further applied as a simultaneous pre-concentration and quantification medium for Fe(II/III), allowing for the facile UV–vis detection of Fe up to 12 μg L−1.

Hydrophobic Natural Eutectic Solvents for the Gas Chromatographic Determination of Suspected Allergens in Fragrances by Dispersive Liquid-Liquid Microextraction

The fragrance industry plays a key role in the global economy, producing a wide range of personal care and household products. However, some fragrance ingredients have been linked to allergic reactions in sensitive people, and their concentrations are regulated at the European level. For this reason, reliable, rapid, and sustainable analytical methods are needed to rapidly detect and quantify these compounds. Recently, a new class of hydrophobic eutectic solvents (HES) has been introduced; they consist of natural terpenoids or phenolic compounds that can be used as hydrogen bond donors (HBD) and acceptors (HBA), and they are more suitable for GC applications due to their higher volatility. In this study, a dispersive liquid–liquid microextraction (DLLME) approach is proposed for the analysis and quantification of a range of allergens in hydroalcoholic perfumes. The optimized method requires only 50 µL of a natural HES (thymol–eugenol), which is readily dispersed by vortexing in 2 mL of sample. After centrifugation, the HES rich phase is diluted in 400 µL EtOH and directly injected into the GC-FID system. The proposed method has been successfully applied in the analysis and quantification of commercial fragrances, demonstrating good enrichment of target allergens and suitability for aqueous matrices analysis.

Hydrophobic eutectic solvents for endocrine disruptors purification from water: Natural and synthetic estrogens study

Effective elimination of natural and artificially synthesized estrogens from water sources and wastewater is very important because even minimal amounts of these substances, considered as endocrine disruptors, are dangerous to humans and wildlife. For the extraction of five estrogens namely estrone, 17α-estradiol, 17β-estradiol, 17α-ethynylestradiol and estriol, hydrophobic eutectic solvents (ES) are newly tested as a green alternative to conventional organic solvents. For this purpose, a series of ES based on a combination of menthol with natural organic acids (octanoic, decanoic and dodecanoic) was prepared in the laboratory. The extraction of estrogens was studied in terms of ES composition, molar ratio of hydrogen bond acceptor and donor, extraction time, extraction rate and reuse. Estrogens were eliminated from the waters at low levels of 10 and 20 μg/mL and their concentrations were monitored using a sensitive HPLC-MS/MS technique. The ES of menthol and octanoic acid in a 1:1 ratio showed the highest extraction efficiency for all estrogens studied, reaching values up to 99.9 % for artificially prepared samples and 97.9 % for real natural and waste waters. Comparable results can be achieved with conventional solvents such as tert-butyl methyl ether, but not with hexane and chloroform. Nevertheless, ES solvents are environmentally sustainable, non-toxic and biodegradable and therefore suitable for industrial wastewater treatment processes.

Separation of Short‐Chain Diols via Formation of Hydrophobic Eutectic Solvents

Separation of Short‐Chain Diols via Formation of Hydrophobic Eutectic Solvents

A pathway to improve detoxification processes by selective extraction of phenols and sugars from aqueous media using sustainable solvents

Integrated biorefineries are the current trend to produce energy, biochemicals and biofuels. A variety of sugar-rich biorefinery streams can be further valorized by fermentation but the presence of inhibitory compounds hinders the fermentation yields. This paper proposes a detoxification method by selective liquid extraction of phenolic compounds using sustainable solvents to improve the fermentation of sugar-rich aqueous streams. Specifically, three hydrophobic eutectic solvents constituted by binary mixtures of octanoic, decanoic or dodecanoic acid (octanoic: decanoic acid 1:1, octanoic: dodecanoic acid 3:1, decanoic: dodecanoic acid 2:1) and three bio-based solvents (2-methyltetrahydrofuran, cyclopentyl methyl ether and limonene) were selected to analyze their capacity to extract representative phenolic compounds (phenol, o-cresol, guaiacol, syringol and vanillin) from aqueous solutions. Extraction efficiencies of individual compounds and mixtures of them were evaluated at different concentrations and temperatures using the proposed solvents. Finally, the liquid extraction of a solution containing 500 mg/L of phenolic compounds and 50 g/L of glucose, as a representative concentration in biorefinery streams, was performed. The distribution of the target compounds in each phase after the extraction process was analyzed by HPLC-DAD in the case of phenolic compounds and HPLC-RI for glucose, and discussed in terms of selectivity. The results obtained are very promising, as the studied solvents can easily extract phenolic compounds but not glucose, which could improve the subsequent sugar fermentation process. In particular, the bio-based solvent cyclopentyl methyl ether provided extraction efficiencies of phenolic compounds above 93%, while that of glucose remained lower than 4%. Finally, all the experimental results were analyzed by means of COSMO-RS methodology, obtaining reliable trends and concluding that the ability of the solvents to form hydrogen bonds with phenolic compounds determines the extraction efficiencies.

Structural Study of a Eutectic Solvent Reveals Hydrophobic Segregation and Lack of Hydrogen Bonding between the Components

An in-depth study of the hydrophobic eutectic solvent formed by butylated hydroxytoluene (BHT) and l-menthol (MEN) in a 1:3 molar ratio has been carried out using an integrated approach that combines differential scanning calorimetry (DSC), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, small- and wide-angle X-ray scattering (SWAXS), and molecular dynamics (MD) simulations. The obtained data have been step-by-step compared to those collected on the eutectic formed by 3,5-di-tert-butyltoluene (TBT) and MEN in the same molar ratio, where TBT is analogous to the BHT without the hydroxyl group. The DSC characterization showed comparable results between the two systems, evidencing that the hydroxyl group of the BHT has little or no impact on the thermal behavior of the BHT:MEN eutectic. Both the FTIR and MD results agree in finding that no hydrogen bond (H-bond) interactions are played by the BHT because of the high steric hindrance suffered by its hydroxyl group so that the only established H-bonds are those between MEN molecules. The incompatibility between the components in terms of H-bonds formation results in hydrophobic segregation promoting the MEN–MEN interactions, which are even more intense than in the pure compound. The three-dimensional arrangement between the components showed a remarkable degree of structural order among the alkyl functional groups, suggesting that the apolar–apolar attraction might be the driving force of the eutectic formation. This picture is translated into the establishment of an intermediate-range organization in solution, as evidenced by the SWAXS data. The overall impact of this study is that of pushing a little bit further the definition of these eutectics, indicated until now as extensively H-bonded systems.

Extraction of antibiotics identified in the EU Watch List 2020 from hospital wastewater using hydrophobic eutectic solvents and terpenoids

The increasing consumption of pharmaceuticals, along with the ineffectiveness of conventional wastewater treatment, has resulted in an increased presence of these pollutants in both drinking water supplies and aquatic environments. The potential adverse health effects and environmental impact of these chemicals are drawing the attention of several bodies around the world. For instance, some antibiotics such as ciprofloxacin, trimethoprim, and sulfamethoxazole have been included in the most recent European Surface Water Watch List under the EU Water Framework Directive (Decision 2020/1161). The present work proposes the use of terpenoids and eutectic solvents, as effective and green solvents with low toxicity, for multicomponent liquid–liquid extraction of ciprofloxacin, trimethoprim, and sulfamethoxazole from ultrapure water and hospital wastewater. The COSMO-RS method was used for a predictive initial solvent screening. Thymol, carvacrol, eutectic solvents (thymol + fatty acids), and conventional solvents (methyl isobutyl ketone and ethyl acetate) were selected to be used in the experiments. The influence of the volumetric S/F ratio, aqueous matrix, and pH was analysed. Conventional solvents show significantly lower overall extraction yields than those observed for eutectic solvents and terpenoids at any pH and matrix. Carvacrol presented the most favourable conditions, reaching overall extraction yields above 98.0% (98.9% for trimethoprim, 99.5% for ciprofloxacin, and 97.0% for sulfamethoxazole) with hospital wastewater at pH 5.0 and S/F ratio of 1.00. Carvacrol showed a feasible operation in a continuous extraction column at room temperature, providing effective reuse and regeneration processes in this study.

Hydrophobic Eutectic Solvents Based on Perfluorinated Hydrogen Bond Donors as Extractants for Dispersive Liquid–Liquid Microextraction

Hydrophobic Eutectic Solvents Based on Perfluorinated Hydrogen Bond Donors as Extractants for Dispersive Liquid–Liquid Microextraction

Cathode recycling of lithium-ion batteries based on reusable hydrophobic eutectic solvents

Hydrophobic eutectic solvents composed of synergistic metal ligands were utilized for recycling cathode materials of lithium-ion batteries as alternatives to inorganic acids and organic solvents in conventional hydrometallurgical cathode recycling.

Analysis of alkylphenols, bisphenols and alkylphenol ethoxylates in microbial-fermented functional beverages and bottled water: Optimization of a dispersive liquid-liquid microextraction protocol based on natural hydrophobic deep eutectic solvents

In this work, the analysis of alkylphenols, bisphenols and alkylphenol ethoxylates in bottled waters, kombuchas and water kefir was performed through a vortex-assisted dispersive liquid–liquid microextraction method based on a natural hydrophobic eutectic solvent. For this purpose, mixtures of monoterpenes and fatty acids were employed. Different factors affecting extraction were optimized and the method was validated in terms of matrix effect, linearity, limits of detection and recovery. Recovery values varied between 70.0 and 124.3% (except for 4-tert-butylphenol: 67.0% and 4-n-nonylphenol: 60.8% in water kefir) and limits of detection were in the range 0.10 ng/L – 2.99 µg/L. Finally, 8 bottled waters, 8 kombuchas and 4 water kefirs were analyzed and 4-tert-octylphenol monoethoxylate was detected in water (20.28 ± 0.99 – 62.08 ± 3.63 µg/L). This is the first application analyzing xenobiotic contaminants in kombucha and water kefir and the first time in which the three types of compounds are simultaneously extracted by dispersive liquid–liquid microextraction.

Structure and dynamics of thymol - fatty acids based deep eutectic solvent investigated by molecular dynamics simulation

The current work focuses on the design of hydrophobic eutectic solvents (HDESs) based on Thymol and fatty acids and the investigation of their dynamical and structural properties. Binary mixtures of Thymol and fatty acids such as Caprylic acid (C8), Decanoic acid (C10), Lauric acid (C12), and Myristic acid (C14) were prepared at different ratios. Molecular dynamics simulations were carried out to evaluate the change in the percentage composition of the designed DESs on the bulk properties at the temperature of 323 K. The percentage composition of the binary mixtures that have the most intermolecular interaction between the donor and the acceptor of the hydrogen bond was selected, and their thermos-physical properties were investigated at different temperatures. The analysis of atom-atom radial distribution functions (RDFs), spatial distribution functions (SDFs), the energy of non-bonded interactions, and the Hydrogen bonding network between Thymol molecules and fatty acids were obtained to understand effective interactions in binary mixture formation. The evidence was found for the hydrogen bonds with the more significant percent occupancies between Thy and FAs in the angular/distance probability region at around 150°−180°/2 Å. The results of MD simulations showed that the intermolecular interactions were impacted in the pure state by interactions between the hydroxyl group of Thymol and fatty acids, and the main interactions interrupt. Dynamical properties of the eutectic mixtures were investigated by the mean-square displacement (MSD) and the self-diffusion. The strong Hydrogen bonding network of binary mixture led to changes in the molecule migration. The intermolecular interaction understanding will aid in determining suitable ratios for the design of eutectic solvents. Finally, we proposed possible explanations for the composition of the appropriate percentage for the formation of the eutectic solvent.

Extractive removal and recovery of bisphenol A from aqueous solutions using terpenoids and hydrophobic eutectic solvents

Bisphenol A (BPA) is a widely used chemical that is found in wastewaters and surface water due to its ineffective removal by conventional water treatment processes. BPA being an endocrine disruptor, regulations and different technologies have been proposed for its treatment. In this work, the use of natural solvents such as terpenoids and eutectic solvents is presented, envisioning a BPA extraction from aqueous solutions based on the hydrophobicity of these sustainable solvents. First, an initial screening of 43 solvents was performed by molecular simulation using the COSMO-RS method. BPA extraction from aqueous solutions was experimentally evaluated with initial BPA concentrations of 5–100 mg/L, and several solvent-to-feed ratios at 303.2 K. Extraction yields > 99% were obtained with eucalyptol, geraniol, and (menthol + camphor) eutectic solvent outperforming conventional solvents. Eucalyptol, geraniol, and (menthol + camphor) have been used in a scaling-up evaluation and reuse in 6 consecutive cycles observing yields in all stages above 98.5% at solvent-to-feed ratios ranging 0.01–0.05. Besides, the solvents were regenerated using back-extraction with NaOH, providing yields above 99.5%. The regenerated solvents showed similar yields to those obtained with fresh solvent, and their chemical stability was checked through FTIR analysis. BPA was recovered by precipitation from the aqueous back-extraction solution, showing by FTIR that no degradation occurs during the extraction, back-extraction, and precipitation processes. For the first time, the complete cycle of extraction with solvent reuse, back-extraction, and precipitation of BPA using eutectic solvents and terpenoids has been studied.

Sustainable Production of Furfural in Biphasic Reactors Using Terpenoids and Hydrophobic Eutectic Solvents

Furfural comes from lignocellulosic biomass that, together with its derived products, has many useful applications in several industries. Furfural is usually obtained via pentose dehydration using a biphasic reactor to extract furfural in situ from its reaction medium. However, the conventional solvents used so far, mainly toluene and methyl isobutyl ketone (MIBK), are harmful to health and the environment. Therefore, hydrophobic natural solvents have been successfully tested in this work to improve the performance of the process from a sustainable point of view. First, 30 natural solvents were screened using the conductor-like screening model for real solvents (COSMO-RS) method to select solvents with high affinity to furfural. From the results obtained in the screening, 14 natural and 2 conventional solvents were selected for experimentation, including thymol, eugenol, toluene, MIBK, and several hydrophobic eutectic solvents formed by thymol. Then, the liquid–liquid extraction of furfural was carried out both in vials and in a reactor, simulating the usual temperature and pH conditions for obtaining furfural. Thymol and eugenol showed extraction yields of 95 and 91%, significantly higher than those of conventional solvents MIBK and toluene, which were 85 and 81%, respectively. Finally, the in situ reaction and extraction of furfural from xylose were performed using the natural solvents eugenol and thymol and the conventional solvent MIBK. Under operating conditions, namely, microwave heating to 443.2 K, 10 min of reaction, and a solvent-to-feed ratio of 1.00, xylose conversion of 96.7%, furfural selectivity of 75.3%, and a furfural production yield of 72.8% from xylose were obtained using eugenol as the organic solvent, with improved outcomes over MIBK and thymol cases, pointing an adequate approach to improve both the effectiveness and the sustainability of the process.

Computational modeling of polydecanediol-co-citrate using benzalkonium chloride-based hydrophobic eutectic solvents: COSMO-RS, reactivity, and compatibility insights

Eutectic solvents (ESs) have been extensively explored in polymer chemistry. Nevertheless, studies utilizing ESs as a constituent of biodegradable poly(diol-co-citrate) (PDCA) polyesters are lacking in the literature. In this work, we propose utilizing benzalkonium chloride (BAC) based hydrophobic eutectic solvents (HESs) as a constituent of PDCAs. Spotting the light on the molecular-level interactions and mechanisms, a theoretical computational study was conducted to evaluate the feasibility of the process by exploiting a combination of geometrical optimizations, COSMO-RS quantum chemical calculations, density functional theory (DFT) calculations, reactivity calculations, and a blends compatibility study. The studied HES is comprised of dodecyldimethylbenzyl ammonium chloride (DDBAC) as an HBA and 1,10-decanediol (D10DO) as the diol HBD at a 1:3 M ratio. Based on the obtained results, it was found that DDBAC-based HESs can be considered as potential solvents for antimicrobial PDCAs. Additionally, the modeling framework reported in this work can be utilized for screening new types of ESs promoting an efficient design approach of new PDCAs with tailored properties based on the choice of the ES’s HBA.

Hydrophobic Eutectic Solvent with Antioxidant Properties: Application for the Dispersive Liquid–Liquid Microextraction of Fat-Soluble Micronutrients from Fruit Juices

Hydrophobic Eutectic Solvent with Antioxidant Properties: Application for the Dispersive Liquid–Liquid Microextraction of Fat-Soluble Micronutrients from Fruit Juices

Extraction and separation of iridium(IV) and rhodium(III) from hydrochloric acid media by a quaternary ammonium-based hydrophobic eutectic solvent

• Efficient extraction of critical metals by a hydrophobic eutectic solvent. • Efficient separation of iridium(IV) and rhodium(III) in hydrochloric acid media. • Mathematical modeling of the extraction mechanism. • Calculation of the fundamental extraction constants. The extraction and separation of iridium(IV) and rhodium(III) from hydrochloric acid solutions by a hydrophobic eutectic solvent composed of tetraheptylammonium chloride and decanoic acid have been studied for the first time. This eutectic solvent selectively extracts iridium(IV) over rhodium(III), the highest separation factor obtained is approximately 20. The effects of the main experimental factors (shaking time, the volume ratio of aqueous to organic phase, hydrochloric acid concentration, and the initial metal concentration in the aqueous phase) on the extraction behavior of iridium(IV) and rhodium(III) have been investigated. Ultraviolet–visible (UV–Vis) spectroscopy was applied to reveal the [IrCl 6 ] 2− complex to be a predominant species attributed to iridium(IV) extraction. To understand the underlying extraction mechanism, the initial iridium(IV) concentration in the aqueous phase has been varied and a corresponding mathematical model has been developed.

Hydrophobic eutectic solvents: Thermophysical study and application in removal of pharmaceutical products from water

Exposure to persistent contaminants presents a risk to humans and animals. Specifically, the occurrence of drugs in aqueous ecosystems is related to the increase in antimicrobial resistance. Several methods to remove them have been studied but most have cost and toxicity drawbacks. Thus, the study of new eco-sustainable procedures is needed as the liquid–liquid extraction with hydrophobic solvents (ESs). In this study, we prepared six ESs mixtures with thymol (Thy) and octanoic acid (Oct) or decanoic acid (Dec) and evaluated their extractive ability in aqueous mixtures of quercetin (Q), nitrofurantoin (NF), or tetracycline (TC). In addition, we measured, correlated, and modelled both the solid–liquid equilibria of the two systems and seven thermophysical properties of the mixtures. From these calculations, we obtained the melting enthalpies of the eutectic points, isobaric thermal expansibilities, intermolecular free lengths, orientational dipolar parameters, thermodynamic properties of the surface, critical temperatures, and activation energies of viscous flow. The perturbed chain statistical associating fluid theory was found to be suitable for predicting the thermodynamic behaviour of these systems. Next, we determined the solubility of the three drugs both in water and in the eutectic mixtures, as well as the efficiency extraction (EE) of the latter. We obtained the highest extraction efficiency for the equimolar [Thy:Oct] mixture, which was the most polar solvent. The values were: EEQ=97.8%, EENF=84.9%, and EETC=95.0%. Further, performing the procedure with three cycles increased these values above 99%. The results showed the highest hydrophobicity for quercetin and the lowest for nitrofurantoin.

Selective separation of lactic, malic, and tartaric acids based on the hydrophobic deep eutectic solvents of terpenes and amides

The selective separation of lactic, malic and tartaric acids coexisting in broth can be improved by effectively regulating the H-bond strength and H-bond competition based on hydrophobic eutectic solvents composed of terpenes and amides.

Hydrophobic deep eutectic solvent-based ultrasonic-assisted liquid-liquid micro-extraction combined with HPLC-FLD for diphenylamine determination in fruit

ABSTRACT In this paper, novel high extraction efficiency hydrophobic eutectic solvents (DESs), n-octanoic acid as a hydrogen bond donor (HBD) and menthol as a hydrogen bond acceptor (HBA), were selected from five hydrophobic DESs to extract trace diphenylamine (DPA) in fruits apple, pear and orange under ultrasonic-assisted liquid-liquid micro-extraction (UA-LLME) technology before high-performance liquid chromatography (HPLC) analysis. Working parameters such as the DESs type, molar ratio, extractant volume, and ultrasonic time of the LLME hydrophobic DESs technology were optimised. Average recoveries between 96% and 108% were obtained on actual samples. This method gave lower detection limit (LOD) than other existing methods due to combining the high-efficiency extraction of hydrophobic DES and high sensitivity of fluorescence detector. This method was sensitive and eco-friendly, and can be used for the determination of trace components in fruits.

A Review of the Use of Eutectic Solvents, Terpenes and Terpenoids in Liquid–liquid Extraction Processes

Diverse and abundant applications of the eutectic solvents have appeared in the last years. Their promising tunable properties, eco-friendly character and the possibility of being prepared from numerous compounds have led to the publication of numerous papers addressing their use in different areas. Terpenes and terpenoids have been employed in the formulation of eutectic solvents, though they also have been applied as solvents in extraction processes. For their hydrophobic nature, renewable character, low environmental impact, cost and being non-hazardous, they have also been proposed as possible substitutes of conventional solvents in the separation of organic compounds from aqueous streams, similarly to hydrophobic eutectic solvents. The present work reviews the application of eutectic solvents in liquid–liquid extraction and terpenes and terpenoids in extraction processes. It has been made a research in the current state-of-the-art in these fields, describing the proposed applications of the solvents. It has been highlighted the scale-up feasibility, solvent regeneration and reuse procedures and the comparison of the performance of eutectic solvents, terpenes and terpenoids in extraction with conventional organic solvents or ionic liquids. Ultimately, it has been also discussed the employ of predictive methods in extraction, the reliability of thermodynamic models in correlation of liquid–liquid equilibria and simulation of liquid–liquid extraction processes.