Hydrophobic Eutectic Solvents Research Articles

Separation of phenols from aqueous streams using terpenoids and hydrophobic eutectic solvents

The separation of phenols from wastewater, mainly in petrochemical plants, refineries, and coal processing plants context, is essential to meet discharge limits. Several technologies have been studied to separate phenols from water, being the liquid–liquid extraction one of the most used so far. Currently, the separation of phenols by extraction is done using organic solvents, such as toluene or methyl isobutyl ketone. In this work, we study the potential use of hydrophobic eutectic solvents and terpenoids as sustainable solvents in the separation of phenol, 2-nitrophenol, and 2-chlorophenol from water. Initially, a screening based on molecular simulation with the COSMO-RS method was carried out to select the most promising alternative solvents. Experimentally, the extraction of the three phenols was studied using four terpenoids, three hydrophobic eutectic solvents, and three conventional organic solvents. Also, the back-extraction of the phenols using an alkaline solution was done to regenerate the solvents, studying the chemical stability of the solvents by FTIR analyses. Among the tested solvents, the most promising extraction and back-extraction yields were obtained for geraniol and linalool. Overall phenols extraction yields of 98.0% and 96.1% for geraniol and linalool respectively, and back-extraction yields >99.5% were obtained, at solvent-to-feed ratio in volume of 0.5. Using both solvents, the extraction of phenols was performed in a packed parallel extraction column to obtain the distribution ratios of each component, further used to simulate a countercurrent extractor by the Kremser method. Finally, to evaluate the use of geraniol and linalool in this process at the industrial scale, the separation of phenols from the wastewater of petrochemical and coal processing plants was simulated using the COSMO-based/Aspen Plus methodology. A complete separation of phenols could be obtained using geraniol and linalool as solvents with a solvent-to-feed ratio of 0.5 and 10 equilibrium stages in the extractor.

Enhancing aqueous systems fermentability using hydrophobic eutectic solvents as extractans of inhibitory compounds

Biomass can be transformed into energy, high value chemicals or bioethanol. Nevertheless, the production of the latter is limited by the presence of inhibitory compounds that hinder the sugar fermentation process. This paper proposes menthol-based Hydrophobic Eutectic Solvents (HESs) as green solvents in the liquid extraction of phenolic compounds from diluted aqueous solutions. In particular, the main goal of the work is to analyse the capacity of the HESs to extract phenolic compounds (phenol, guaiacol and syringol) and glucose (as model sugar), since both types of compounds are present in the aqueous phase generated after washing with water the oil obtained in the fast pyrolysis of the biomass. As this is a preliminary study, two model mixtures constituted by solute (phenolic compound or glucose) and deionized water were used. Once HESs were prepared using menthol and three organic acids (octanoic acid, decanoic acid and dodecanoic acid), liquid–liquid extractions were performed in order to test the ability of these solvents to extract the abovementioned compounds from water. Firstly, stirring and centrifuging times were optimized and the effect of varying the solvent/feed ratio and the initial concentration of the solution {phenolic compound + water} were studied. Afterwards, since the goal of this work is to remove phenols from water to enhance sugars fermentability, the liquid extraction of glucose from water using the same HESs were also experimentally carried out at the optimized conditions. The obtained results are very promising, as HESs can easily extract phenols but not glucose, which would improve the subsequent sugar fermentation process.

Predicting the density and viscosity of hydrophobic eutectic solvents: towards the development of sustainable solvents

The interest in green and sustainable solvents has been dramatically increasing in recent years because of the growing awareness of the impact of classical organic solvents on environmental pollution and human health.

Sustainable Recovery of Volatile Fatty Acids from Aqueous Solutions Using Terpenoids and Eutectic Solvents

Volatile fatty acids (VFAs) are produced in the anaerobic digestion of urban or food wastes and sewage sludge. The interest in these compounds has increased because of their use as platform chemicals. In this paper, the application of natural terpenoids and eutectic solvents to sustainably recover VFAs from aqueous solutions by extraction has been evaluated. First, a screening of solvents has been done using COSMO-RS, selecting three terpenoids: geraniol, citral, and eugenol, and two hydrophobic eutectic solvents formed by octanoic acid and menthol or thymol. These solvents have been tested in the extraction of acetic, propionic, butyric, and valeric acids. The highest yields were obtained using geraniol and the (octanoic acid + thymol) eutectic solvent, being comparable or higher than those for organic solvents from the literature. The back-extraction of the VFAs from both solvents has been studied using NaOH and Na2CO3 solutions, concluding that the eutectic solvent is not chemically stable to be reused...

Sustainable approach for lycopene extraction from tomato processing by-product using hydrophobic eutectic solvents.

Lycopene, a non-polar antioxidant compound with important effects on human health and wide commercial applications, was extracted from tomato processing wastes using innovative hydrophobic eutectic mixtures (HEMs) replacing traditional organic solvents. HEMs were prepared using DL-menthol as hydrogen-bond acceptor (HBA) and lactic acid as hydrogen-bond donor (HBD), and the ultrasound-assisted extraction (UAE) was optimized using a Box-Behnken design to evaluate extraction conditions: extraction temperature (°C), molar ratio of eutectic mixture (moles HBA: mol HBD), solvent to sample ratio (volume to mass, mL/g), and extraction time (min), with lycopene extraction yield (µg/g d.w.) as the response variable. Optimization of parameters was performed using response surface methodology, and the optimized extraction conditions were determined to be 70°C, 8:1mol HBA/mol HBD, 120mL/g solvent: sample, and 10min. The experimental optimal yield was 1446.6µg/g, in agreement with the predicted optimal yield, indicating the validity of the model. This new technique for lycopene extraction, using a HEM as extraction solvent in replacement of hazardous organic solvents, and tomato pomace as source material, represents a viable and more sustainable approach for obtaining a high value-added bioactive compound, and can contribute towards the development of greener extraction processes.

Designing Eco-Sustainable Dye-Sensitized Solar Cells by the Use of a Menthol-Based Hydrophobic Eutectic Solvent as an Effective Electrolyte Medium.

The use of a hydrophobic eutectic solvent based on dl-menthol and a naturally occurring acid such as acetic acid has been tested as an eco-friendly electrolyte medium in dye-sensitized solar cells. In the presence of a de-aggregating agent and a representative hydrophobic organic photosensitizer, the corresponding devices displayed relatively good power conversion efficiencies in very thin active layers. In particular, the higher cell photovoltage detected in comparison to devices based on toxic and volatile organic compounds may stem from a more efficient interface interaction, as suggested by electrochemical impedance spectroscopy studies showing greater charge recombination resistance and electron lifetime.

Hydrophobic Deep Eutectic Solvents Incorporating Trioctylphosphine Oxide: Advanced Liquid Extractants

A low viscosity, hydrophobic eutectic solvent based on trioctylphosphine oxide (TOPO) has been developed and characterized, and its use as an extractant demonstrated for liquid–liquid separation of uranyl nitrate from aqueous acid. This strategy of liquefying the active extracting agent as a eutectic liquid produced liquids that contain an intrinsically high concentration of TOPO (ca. 80 wt %, 1.875 mol L–1 at χTOPO = 0.50) and renders the use of an organic (hydrocarbon) diluent redundant.

Tunable Hydrophobic Eutectic Solvents Based on Terpenes and Monocarboxylic Acids

Recently, some works claim that hydrophobic deep eutectic solvents could be prepared based on menthol and monocarboxylic acids. Despite of some promising potential applications, these systems were poorly understood, and this work addresses this issue. Here, the characterization of eutectic solvents composed of the terpenes thymol or l(−)-menthol and monocarboxylic acids is studied aiming the design of these solvents. Their solid–liquid phase diagrams were measured by differential scanning calorimetry in the whole composition range, showing that a broader composition range, and not only fixed stoichiometric proportions, can be used as solvents at low temperatures. Additionally, solvent densities and viscosities close to the eutectic compositions were measured, showing low viscosity and lower density than water. The solvatochromic parameters at the eutectic composition were also investigated aiming at better understanding their polarity. The high acidity is mainly provided by the presence of thymol in the m...

Sustainable hydrophobic terpene-based eutectic solvents for the extraction and separation of metals.

Sustainable hydrophobic eutectic solvents, composed of low-priced and biodegradable terpenes and fatty acids, were used for the extraction and separation of Cu(ii) from other transition metals in mildly acidic solutions. Multiple parameters were evaluated for metal extraction and the hydrophobic eutectic solvent was successfully recovered and reused.

Menthol-based Eutectic Mixtures: Hydrophobic Low Viscosity Solvents

Inspired by one of the major problems in the pharmaceutical industry, we advantageously used the formation of eutectic mixtures to synthesize new solvents. The aim of this work is to identify low viscosity, cheap, biodegradable and hydrophobic eutectic solvents from natural resources. Consequently, novel eutectic mixtures based on dl-menthol and naturally occurring acids, namely pyruvic acid, acetic acid, l-lactic acid, and lauric acid, were synthesized and are here reported for the first time. The obtained dl-menthol-based eutectic mixtures were analyzed using NMR and FTIR spectroscopy in order to check their structures and purities and to confirm the interaction of the two compounds leading to the eutectic formation. Important solvent thermophysical properties, such as density and viscosity, of the prepared eutectic solvents with different water contents (dried and water-saturated) were measured. Finally, taking advantage of their hydrophobic character, namely the formation of two phases with water at r...