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 mixture, while l­(−)-menthol plays the major role on the hydrogen-bond basicity. The measured mutual solubilities with water attest to the hydrophobic character of the mixtures investigated. The experimental solid–liquid phase diagrams were described using the PC-SAFT equation of state that is shown to accurately describe the experimental data and quantify the small deviations from ideality.

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Aiming at providing an extensive characterization of the solid−liquid equilibria (SLE) of deep eutectic solvents (DESs), the phase diagrams of nine eutectic mixtures composed of choline chloride ([Ch]Cl) and (poly)carboxylic acids, commonly reported in the literature as DESs, were measured experimentally. Contrarily to the behavior reported for eutectic mixtures composed of [Ch]Cl (hydrogen-bond acceptor, HBA) and monofunctional hydrogen-bond donors (HBD) such as fatty acids and fatty alcohols, which have recently been shown to be almost ideal mixtures, a significant decrease of the melting temperature, at the eutectic point, was observed for most of the systems studied. This melting temperature depression was attributed to a pronounced nonideality of the liquid phase induced by the strong hydrogen-bond interactions between the two mixture components. Perturbed-chain statistical associating fluid theory (PC-SAFT) was used to describe these interactions physically. PC-SAFT allowed accurately modeling the experimental phase diagrams over the entire concentration and temperature ranges. Depending on the kind of mixture, up to two temperature-independent binary interaction parameters between HBA and HBD were applied. The PC-SAFT approach was used to provide trustworthy information on the nonideality of the liquid phase (expressed as the activity coefficients of HBA and HBD) as well as to estimate the eutectic points coordinates. The experimental data along with the modeling results allowed us to infer about the importance of the HBD's chemical structure on the formation of [Ch]Cl-based DESs.

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Small change–large effect: An added para-methyl group on the aryl ring in the 1-aryl-3-alkyl-imidazolium motif of TAAILs leads to well-separated metal nanoparticles.

Precursor solubility is a crucial factor in industrial applications, dominating the outcome of reactions and purification steps. The outcome and success of thermodynamic modelling of this industrially important property with equations of states, such as Perturbed‐Chain Statistical Associating Fluid Theory (PC‐SAFT), vastly depends on the quality of the pure‐component parameters. The pure‐component parameters for low‐volatile compounds such as ionic liquids (ILs) have been commonly estimated using mixture properties, e. g. the osmotic pressure of aqueous solutions. This leads to parameters that depend on the solvent, and transferability to other mixtures often causes poor modeling results. Mixture‐independent experimental properties would be a more suitable basis for the parameter estimation offering a way to universal parameter sets. Model parameters for ILs are available in the literature [10.1016/j.fluid.2012.05.029], but they were estimated using pure‐IL density data. The present work focuses on a step towards a more universal estimation strategy that includes new experimental vapor‐pressure data of the pure IL. ILs exhibit an almost negligible vapor pressure in magnitude of usually 10−5 Pa even at elevated temperatures. In this work, such vapor‐pressure data of a series of 1‐ethyl‐3‐methyl‐imidazolium‐based [C2mim]‐ILs with various IL‐anions (e. g. tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]−, bis(trifluoromethylsulfonyl)imide [NTf2]−) were experimentally determined and subsequently used for PC‐SAFT parameter estimation. The so‐determined parameters were used to predict experimental molecular precursor solubility in ILs and infinitely diluted activity coefficients of various solvents in ILs. The parameters were further compared to modeling results using classical parametrization methods (use of liquid‐density data only for the molecular PC‐SAFT and the ion‐based electrolyte PC‐SAFT). As a result, the modeled precursor solubilities using the new approach are much more precise than using the classical parametrization methods, and required binary parameters were found to be much smaller (if needed). In sum, including the pure‐component vapor‐pressure data of ILs opens the door towards parameter estimation that is not biased by mixture data. This procedure might be suitable also for polymers and for all kind of ionic species but needs extension to ion‐specific parametrization in the long term.

Sour-gas absorption is the main unit operation used in refineries and petrochemical and natural gas processing plants for the effective reduction of climate-wrecking gases, mainly CO 2 and H 2 S. Absorption is typically accomplished in an aqueous solvent mixture. The solvent mixture is vastly dependent on the application range; it might contain chemical solvents (amines), activators, and physical solvents. In this work, the vapor−liquid equilibria for absorption of the sour gases CO 2 and H 2 S was investigated in systems containing the chemical solvent methyl diethanolamine (MDEA) and the physical solvents tetrahydrothiophene-1,1-dioxide (sulfolane) or the ionic liquid 1-butyl-3-methylimidazolium acetate. The solubilities of CO 2 and H 2 S were predicted and validated using experimental literature data in a broad range of temperature (313−373 K), sour-gas loading (up to 2 moles gas per moles of MDEA), and pressure (up to 180 bar) at constant MDEA weight fraction (20.9 wt %) and sulfolane weight fraction (30.5 wt %). The equation-of-state electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) was utilized in this work for the predictions combined with the Born term to physically correctly describe the Gibbs energy of solvation of ions in the aqueous mixture of chemical and physical solvents; this was introduced in a recent work [Bulow, M. et al. Fluid Phase Equilib. 2021, 535, 112967]. Using this approach allowed reducing the total number of binary interaction parameters in these systems of maximum 11 species to a minimum; these parameters were fitted exclusively to data of binary mixtures. The ePC-SAFT predictions of the gas solubility were most accurate at low sour-gas loadings and high temperatures. This work provides a thermodynamic framework for the solvent selection for sour-gas absorption in a broad range of conditions. This enables a realistic decrease in experimental effort for solvent selection in sour-gas absorption.