Selection of Ionic Liquids for Enhancing the Gas Solubility of Volatile Organic Compounds

A systematic thermodynamic analysis has been carried out for selecting cations and anions to enhance the absorption of volatile organic compounds (VOCs) at low concentration in gaseous streams by ionic liquids (ILs), using COSMO-RS methodology. The predictability of computational procedure was validated by comparing experimental and COSMO-RS calculated Henry’s law constant data over a sample of 125 gaseous solute–IL systems. For more than 2400 solute–IL mixtures evaluated, including 9 solutes and 270 ILs, it was found that the lower the activity coefficient at infinite dilution (γ^∞) of solutes in the ILs, the more the exothermic excess enthalpy (<i>H</i>^E) of the equimolar IL–solute mixtures. Then, the solubility of a representative sample of VOC solutes, with very different chemical nature, was screened in a wide number of ILs using COSMO-RS methodology by means of γ^∞ and <i>H</i>^E parameters, establishing criteria to select the IL structures that promote favorable solute–solvent intermolecular interactions. As a result of this analysis, an attempt of classification of VOCs respect to their potential solubility in ILs was proposed, providing insights to rationally select the cationic and anionic species for a possible development of absorption treatments of VOC pollutants based on IL systems

Deterpenation of Citrus Essential Oils Using Glycerol-Based Deep Eutectic Solvents

Citrus essential oils are complex hydrocarbon mixtures mainly composed of terpenes and terpenoids and are widely used as raw materials in food, pharmaceutical, and fine chemical industries. However, essential oil deterpenation (i.e., separation of terpenes and terpenoids) is required to preserve the quality of the final product for practical applications. Currently, there is a need to find efficient and environmentally friendly solvents to replace the harmful volatile organic compounds that are conventionally used as extraction solvents. Therefore, alternative solvents with more benign and environmentally friendly characteristics are crucial to develop sustainable citrus essential oil deterpenation processes. In this work, biorenewable deep eutectic solvents (DES) composed of glycerol (Gly) and choline chloride (ChCl) are evaluated as sustainable solvents for citrus essential oil deterpenation, using model mixtures and real citrus crude orange essential oils (COEO). The liquid–liquid extraction process for essential oil deterpenation using DES was performed at 298.15 K and 101.3 kPa, and the solvent performance was evaluated in terms of the experimental solute distribution coefficients and selectivity values, which were compared against those predicted using the conductor-like screening model for real solvents (COSMO-RS). The effect of solvent composition (i.e., hydrogen bond acceptor/donor ratio) and the addition of water (pure DES vs diluted DES) were also explored. Overall results indicate the feasibility of using DES as extraction solvents for citrus essential oil deterpenation, with pure ChCl:Gly 1:2 providing the highest extraction yield, while the addition of water decreased the distribution coefficient but increased the selectivity of the process

Solubility and Diffusivity of CO₂ in [hxmim][NTf₂], [omim][NTf₂], and [dcmim][NTf₂] at <i>T</i> = (298.15, 308.15, and 323.15) K and Pressures up to 20 bar

Solubilities and diffusion coefficients of CO₂ absorption in the ionic liquids (ILs) [hxmim]­[NTf₂], [omim]­[NTf₂], and [dcmim]­[NTf₂] at temperatures of (298.15, 308.15, and 323.15) K and pressures up to 20 bar were obtained by thermogravimetric measurements using a high pressure sorption analyzer with magnetic suspension balance operating in dynamic mode. The effect of the length of the alkyl side chain of the imidazolium cation and the operating conditions on the thermodynamics and kinetics of the CO₂ absorption process in ILs were evaluated. Absorption data confirmed that the CO₂ solubility in ILs increases with increasing length of the alkyl side chain of the cation and with decreasing temperatures and increasing pressures. The diffusion coefficients of CO₂, calculated by applying a mass diffusion model, decrease with increasing lengths of the alkyl side chain of the cation and increase with both temperature and pressure of absorption. These results illustrate the importance of considering both thermodynamic and kinetic aspects in the selection of an IL as absorbent and the operating conditions for developing absorption processes based on ILs. In addition, the empirical correlation of Wilke–Chang was successfully applied as an alternative to estimate the diffusion coefficients of the systems

Diffusion Coefficients of CO₂ in Ionic Liquids Estimated by Gravimetry

The estimation of diffusion coefficients of CO₂ in ionic liquids by gravimetry is analyzed with the aim of establishing a measurement method that provides consistent values of diffusivity. Absorption kinetic curves of CO₂ in three common ILs were measured at different temperatures (293–323 K) and pressures (1–20 atm) by using a high pressure sorption analyzer with magnetic suspension balance operating in dynamic mode. A mass diffusion model widely used in the literature was applied to estimate effective diffusion coefficients for CO₂–IL systems from time-dependent absorption data. The measuring conditions (IL mass, dimension of sample container, gas flow) in the dynamic absorption experiments were modified to verify the assumptions of the diffusion model. Obtained results were compared to available data. In addition, the suitability of theoretical methods commonly used for estimating diffusion coefficients of CO₂ in ILs was analyzed, in order to select a computational approach for preliminary selection of ILs with favorable transport properties for CO₂ capture

Anion Effects on Kinetics and Thermodynamics of CO₂ Absorption in Ionic Liquids

A thermogravimetric technique based on a magnetic suspension balance operating in dynamic mode was used to study the thermodynamics (in terms of solubility and Henry’s law constants) and kinetics (i.e., diffusion coefficients) of CO₂ in the ionic liquids [bmim]­[PF₆], [bmim]­[NTf₂], and [bmim]­[FAP] at temperatures of 298.15, 308.15, and 323.15 K and pressures up to 20 bar. The experimental technique employed was shown to be a fast, accurate, and low-solvent-consuming method to evaluate the suitability of the ionic liquids (ILs) to be used as CO₂ absorbents. Thermodynamic results confirmed that the solubility of CO₂ in the ILs followed the order [bmim]­[FAP] > [bmim]­[NTf₂] > [bmim]­[PF₆], increasing with decreasing temperatures and increasing pressures. Kinetic data showed that the diffusion coefficients of CO₂ in the ILs followed a different order, [bmim]­[NTf₂] > [bmim]­[FAP] > [bmim]­[PF₆], increasing with increasing temperatures and pressures. These results evidenced the different influence of the IL structure and operating conditions on the solubility and absorption rate of CO₂, illustrating the importance of considering both thermodynamic and kinetic aspects to select adequate ILs for CO₂ absorption. On the other hand, the empirical Wilke–Chang correlation was successfully applied to estimate the diffusion coefficients of the systems, with results indicating the suitability of this approach to foresee the kinetic performance of ILs to absorb CO₂. The research methodology proposed herein might be helpful in the selection of efficient absorption solvents based on ILs for postcombustion CO₂ capture

Flowsheet Simulation of Cobalt–Nickel Separation by Solvent Extraction with Trihexyl(tetradecyl)phosphonium Chloride

Solvent extraction is widely used for selective separation of metals from solutions. Ionic liquids are showing potential for this purpose. To date, little research has focused on design, operation, and optimization of solvent extraction flowsheets using ionic liquids. This work addresses this gap in knowledge, aiming to support development, design, and optimization of such solvent extraction processes. In this work, a general flowsheet simulation model is developed and applied for the case of cobalt–nickel separation using ionic liquid trihexyl­(tetradecyl)­phosphonium chloride ([P₆₆₆₁₄]­Cl). All components are treated as distributing between the two phases and are modeled using distribution coefficient models derived from published experimental data and ab initio computational results. The rate of mass transfer between the two phases is calculated using a mass transfer model. Simulation results are shown to be generally in good agreement with published experimental results

Excess Enthalpy of Monoethanolamine + Ionic Liquid Mixtures: How Good are COSMO-RS Predictions?

Mixtures of ionic liquids (ILs) and molecular amines have been suggested for CO₂ capture applications. The basic idea is to replace water, which volatilizes in the amine regeneration step and increases the parasitic energy load, with a nonvolatile ionic liquid solvent. To fully understand the thermodynamics of these systems, here experimental excess enthalpies for binary mixtures of monoethanolamine (MEA) and two ILs: 1-hexyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide, [hmim]­[NTf₂], and 1-(2-hydroxyethyl)-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide, [OHemim]­[NTf₂], were obtained by calorimetry, using a Setaram C80 calorimeter, over the whole range of compositions at 313.15 K. Since it is the temperature derivative of the Gibbs energy, enthalpy is a sensitive measure of intermolecular interactions. MEA + [hmim]­[NTf₂] is endothermic and MEA + [OHemim]­[NTf₂] is exothermic. The reliability of COSMO-RS to predict the excess enthalpy of the (MEA+IL) systems was tested based on the implementation of two different molecular models to define the structure of the IL: the IL as separate cation and anion [C+A] and the IL as a bonded single specie [CA]. Quantum-chemical calculations were performed to gain additional insight into the intermolecular interactions between the components of the mixture. For MEA + [hmim]­[NTf₂] both the [C+A] and [CA] models predict endothermic behavior, but the [CA] model is in better agreement with the experimental results. For MEA + [OHemim]­[NTf₂] the [C+A] model provides the best match to the experimental exothermic results. However, what is really surprising is that two different conformations of the cation–anion pair with nearly identical energies in the [CA] model result in completely different (exothermic vs endothermic) predictions of the excess enthalpy. Nonetheless, the results do show that the influence of the structure of the IL on the thermodynamic behavior of the mixture (endothermic vs exothermic) can be attributed to hydrogen bonding between the cation and the MEA molecule. However, this study highlights the importance of carefully selecting the molecular model and conformation in order to obtain even qualitatively correct predictions with COSMO-RS. The fact that even very slightly different conformations of the IL can drastically change the thermodynamic estimations using COSMO-RS is of significant concern. Overall, we believe the present work provides a better understanding of the behavior of mixtures involving amines and ILs, which is an important aspect to consider when evaluating the use of such solvent mixtures in CO₂ capture technologies

Choline Chloride-Based Deep Eutectic Solvents in the Dearomatization of Gasolines

The extraction of aromatic hydrocarbons from reformer and pyrolysis gasolines is currently performed by liquid–liquid extraction using organic solvents. Deep eutectic solvents (DES) are being widely studied as environmentally benign alternatives to conventional solvents since DES can be prepared using nontoxic and renewable chemicals. In this work, we have studied for the first time the application of DES in the extraction of aromatic hydrocarbons from reformer and pyrolysis gasolines. We have tested six choline chloride-based DES formed by ethylene glycol, glycerol, levulinic acid, phenylacetic acid, malonic acid, and urea as hydrogen bond donors. COSMO-RS method was employed to predict the performance of the DES in the extraction of aromatics, whereas experimental results indicate that DES formed by choline chloride and levulinic acid has exhibited the most adequate extractive and physical properties. Afterward, the simulation and optimization of the whole process for extraction of aromatics, recovery of extracted hydrocarbons, and regeneration of the solvent have been performed. The proposed process of dearomatization could work at moderate temperatures using a cheap, sustainable, and nontoxic solvent

COSMO-RS Studies: Structure–Property Relationships for CO₂ Capture by Reversible Ionic Liquids

The quantum-chemical approach COSMO-RS was used to develop structure–property relationships of reversible ionic-liquid (RevIL) solvents for CO₂ capture. Trends predicted for the thermodynamic properties of the RevILs using COSMO-RS, such as CO₂ solubility, solvent regeneration enthalpy, and solvent reversal temperature, were verified by experimental data. This method was applied to a range of structures, including silylamines with varying alkyl chain lengths attached to the silicon and amine functionality, silylamines with fluorinated alkyl chains, sterically hindered silylamines and carbon-based analogues. The energetics of CO₂ capture and release and the CO₂ capture capacities are compared to those of the conventional capture solvent monoethanolamine. The results of this study suggest that the simple COSMO-RS computational approaches reported herein can act as a guide for designing new RevILs. COSMO-RS allows for the determination of the relative thermodynamic properties of CO₂ in these and related systems