• Journal LogoNew Experimental Data and Modeling of Glymes: Toward the Development of a Predictive Model for Polyethers
    Industrial & Engineering Chemistry Research (2017)  doi10.1021/acs.iecr.7b01532

    The design and optimization of industrial processes relies on the availability of robust and accurate models and equations of state (EoSs). Considering the further advancement of the use of soft-SAFT (one version of statistical associating fluid theory) EoS, toward its implementation in industrial processes, a methodology to determine the molecular model and transferable molecular parameters of glymes is discussed herein. In addition to the commonly used vapor pressure and saturated liquid densities, the description of the temperature and pressure effect is improved by including one additional density–pressure and one isothermal compressibility isotherm (both at 323 K) for the molecular parameter optimization. For the guiding of the selection and optimization of the soft-SAFT EoS molecular model and parameters, new high-pressure density data (pρT) and derived properties, such as isothermal compressibility and isobaric thermal expansion, of eight glymes (glycol ethers) have been determined in wide ranges of temperatures (283–363 K) and pressures (0.1–95 MPa). The selected molecular model (considering that only the hydroxyl end groups are able to establish associative interactions) and its parameters provide an excellent description of the experimental data, being able to predict the characteristic crossover point observed for the isobaric thermal expansivities. The robustness and enhanced physical meaning of the molecular model and molecular parameters allow the use of correlations with the molecular weight. The transferability of the proposed molecular parameters is further used to predict the liquid densities for PEGDME250 (a blend of di alkyl ethers similar to the Selexol solvent).

  • Journal LogoChameleonic Behavior of Ionic Liquids and Its Impact on the Estimation of Solubility Parameters
    Journal of Physical Chemistry B 115 (2011) 12879-12888 doi10.1021/jp207369g

    The possibility of developing a scale for solubility parameters, with the purpose of predicting the performance and aiding the selection of ILs, was evaluated. For the estimation of solubility parameters, infinite-dilution activity coefficient data were used. The results allowed the identification of a curious behavior for ILs that seem to present more than one solubility parameter, acting as polar molecules in some situations and as nonpolar molecules in others, depending on the medium. This behavior was confirmed by solubility measurements of [C4MIM][PF6] in solvent mixtures. In this work, the solubility parameters were also estimated from other properties, namely, viscosities and enthalpies of vaporization, and the relation between the various sets of solubility parameters is discussed. The results obtained suggest that, given the complexity of IL molecules and their liquid phases, a one-dimensional scale for solubility parameters that is able to characterize these fluids is not feasible.Consectetuer adipiscing elit. Donec eu massa vitae arcu laoreet aliquet.

  • Journal LogoThe Polarity Effect Upon the Methane Solubility in Ionic Liquids: a Contribution for the Design of Ionic Liquids for Enhanced CO2/CH4 and H2S/CH4 Selectivities
    Energy & Environmental Science 4 (2011) 4614-4619 doi10.1039/c1ee01599k

    Aiming at designing ionic liquids for the purification of natural gas, the solubility of methane in ionic liquids is investigated here through the measurement of the solubilities of methane in four ionic liquids (ILs), in a wide range of molar fractions, temperature and pressures. With the exception of the phosphonium-based IL, which behaves as an almost ideal solution, the other ionic liquids show strong positive deviations from ideality, resulting from non-favorable interactions between CH4 and the ILs. The results indicate that the non-ideality of the solution increases, and the solubility decreases, with the polarity of the ionic liquid. The effect of the ionic liquid polarity on the CO2/CH4 and H2S/CH4 selectivities is evaluated here. The ionic liquids studied here present the largest CO2/CH4 and H2S/CH4 selectivities ever reported. The selectivity models previously proposed in the literature are tested against these new experimental data and are shown to fail. Furthermore, it is shown that describing the ILs' polarity using the Kamlet–Taft parameters, the CO2/CH4 and H2S/CH4 selectivities correlate well with the β-parameter providing a key to the design of ionic liquids with enhanced selectivities.

  • Journal LogoNon-ideality of Solutions of NH3, SO2, and H2S in Ionic Liquids and the Prediction of Their Solubilities Using the Flory−Huggins Model
    Energy & Fuels 24 (2010) 6662-6666 doi10.1021/ef100988z

    The non-ideality of solutions of light compounds, such as SO2, NH3, and H2S, in ionic liquids (ILs) is studied here using experimental vapor−liquid equilibrium (VLE) data previously published. The data available for systems of ILs with SO2, NH3, and H2S show that these systems present negative deviations to the ideality in the liquid phase and that these deviations are dominated by entropic effects. It is shown here that, for the solutions of SO2 and NH3 in ILs, the deviations from ideality and the gas solubility can be predicted using the Flory−Huggins model. For H2S, a positive deviation to the non-ideality that arises from the enthalpic effects somewhat decreases the quality of the description of the experimental data by the Flory−Huggins model predictions.

  • Journal LogoOn the Nonideality of CO2 Solutions in Ionic Liquids and Other Low Volatile Solvents
    Journal of Physical Chemistry Letters 1 (2010) 774-780 doi10.1021/jz100009c

    The nonideality of CO2 solutions in ionic liquids and other low volatile solvents, with which CO2 is known to form electron donor−acceptor (EDA) complexes, is here investigated. It is shown that the deviations from the ideality observed are not related with the stability of the EDA complex formed, and in most cases these deviations are small and dominated by entropic effects. For this reason, when the CO2 concentration is expressed in molality, the pressure versus concentration phase diagrams of CO2 in nonvolatile solvents are, within the uncertainty of the experimental data, solvent independent. Following this approach, a correlation for the solubility of CO2 in nonvolatile solvents, valid for pressures up to 5 MPa and temperatures ranging from room temperature up to 363 K, is here proposed. These results are tested with success by measuring the solubility of CO2 in [THTDP][Cl] to show that, in such heavy ionic liquid the solubility, although identical in molality units, if expressed in mol fractions, it is larger than that in [BMIM][NTf2].

  • Journal LogoPredictive Methods for the Estimation of Thermophysical Properties of Ionic Liquids
    RSC Advances 2 (2012) 7322-7346 doi10.1039/C2RA20141K

    While the design of products and processes involving ionic liquids (ILs) requires knowledge of the thermophysical properties for these compounds, the massive number of possible distinct ILs precludes their detailed experimental characterization. To overcome this limitation, chemists and engineers must rely on predictive models that are able to generate reliable values for these properties, from the knowledge of the structure of the IL. A large body of literature was developed in the last decade for this purpose, aiming at developing predictive models for thermophysical and transport properties of ILs. A critical review of those models is reported here. The modelling approaches are discussed and suggestions relative to the current best methodologies for the prediction of each property are presented. Since most of the these works date from the last 5 years, this field can still be considered to be in its infancy. Consequently, this work also aims at highlighting major gaps in both existing data and modelling approaches, identifying unbeaten tracks and promising paths for further development in this area.

  • Journal LogoA New Microebulliometer for the Measurement of the Vapor-Liquid Equilibrium of Ionic Liquid Systems
    Fluid Phase Equilibria 354 (2012) 156-165 doi10.1016/j.fluid.2013.06.015

    Over the last decade ionic liquids appeared as potential entrainers for extractive distillation processes. However experimental vapor–liquid equilibrium data for ionic liquid containing systems is still scarce since most conventional equilibrium cells are not adequate for these systems. To overcome that limitation a new isobaric microebulliometer, operating at pressures ranging from 0.05 to 0.1 MPa and requiring a sample volume lower than 8 mL was developed and validated in this work. The new apparatus was used to determine isobaric VLE data at pressures of 0.05, 0.07 and 0.1 MPa for eight binary mixtures of 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), 1-butyl-3-methylimidazolium chloride ([C4mim][Cl]), 1-hexyl-3-methylimidazolium chloride ([C6mim][Cl]), and choline chloride ([N111(2OH)][Cl]) with water and ethanol. The experimental data here measured were correlated with the NRTL model.

  • Journal LogoHigh Pressure Separation of Greenhouse Gases from Air with 1-ethyl-3-methylimidazolium methyl-phosphonate
    International Journal of Greenhouse Gas Control 19 (2013) 299-309 doi10.1016/j.ijggc.2013.09.007

    Increasing pollutants emissions, along with the limitations present on the existing control methods and stricter legislation to come, demand the development of new methods to reduce them. Ionic liquids (ILs) have been attracting an outstanding attention during the last decade and rose as a promising class of viable solvents to capture pollutants and for gas separation processes. As part of a continuing effort to develop an ionic liquid based process for high pressure capture of greenhouse gases, the phase equilibria of carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4) and nitrogen (N2) in 1-ethyl-3-methylimidazolium methyl-phosphonate ([C2mim][CH3OHPO2]) were studied in this work. Experimental measurements for the CO2, N2O, CH4 and N2 solubilities in [C2mim][CH3OHPO2] were carried out for gases mole fractions ranging from (0.018 to 0.504), in the temperature range (293.23 to 363.34) K and for pressures from (1.16 to 87.61) MPa. The particular behavior of the selected highly polar ionic liquid is here shown for the first time through the reported experimental data. ...

  • Journal LogoHigh Pressure Density and Solubility for the CO2 + 1-ethyl-3-methylimidazolium Ethylsulfate System
    The Journal of Supercritical Fluids 88 (2014) 46-55 doi10.1016/j.supflu.2014.01.011

    The solubility and density of the CO2 + 1-ethyl-3-methylimidazolium ethylsulfate system was investigated. The carbon dioxide solubility in the IL was measured in the temperature range (273 to 413) K, for pressure up to 5 MPa and CO2 mole fractions ranging from 0.02 to 0.5 using the isochoric method, while the system density was carried out at temperatures ranging from (278.15 to 398.15) K, pressures from (10 to 120) MPa and 0.2, 0.4, 0.7 and 0.8 CO2 mole fractions. Similar to what was previously observed for phosphonate-based ILs, the ionic liquid high polarity leads to positive deviations from ideality resulting from unfavorable interactions with the CO2.
    The results from the density and solubility derived properties, show that the system presents important negative excess molar volumes, over the whole range of compositions and temperatures and a negative entropy of solvation that suggests an increase in ordering of the solvent molecules surrounding the solute. The observed negative excess molar volumes result from the large difference between the molecular volumes of the species involved, with the small carbon dioxide molecules occupying the empty spaces between the larger IL ions, supporting the notion that the carbon dioxide, upon dissolution, occupies essentially the bulk free volume since the IL does not significantly expand upon gas absorption. ...

  • Journal LogoVapor-Liquid Equilibria of Water + Alkylimidazolium-based Ionic Liquids: Measurements and Perturbed-Chain Statistical Associating Fluid Theory Modeling
    Industrial and Engineering Chemistry Research 53 (2014) 37373748 doi10.1021/ie4041093

    The industrial application of ionic liquids (ILs) requires the knowledge of their physical properties and phase behavior. This work addresses the experimental determination of the vapor–liquid equilibria (VLE) of binary systems composed of water + imidazolium-based ILs. The ILs under consideration are 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium tosylate, 1-butyl-3-methylimidazolium trifluoroacetate, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium methanesulfonate, and 1-butyl-3-methylimidazolium acetate, which allows the evaluation of the influence of the IL anion through the phase behavior. Isobaric VLE data were measured at 0.05, 0.07, and 0.1 MPa for IL mole fractions ranging between 0 and 0.7. The observed increase in the boiling temperatures of the mixtures is related with the strength of the interaction between the IL anion and water. The Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) was further used to describe the obtained experimental data. ...

  • Journal LogoCarbon Dioxide Solubility in Aqueous Solutions of NaCl: Measurements and Modeling with Electrolyte Equations of State
    Fluid Phase Equilibria 388 (2015) 100-106  doi10.1016/j.fluid.2014.12.043

    A new high pressure cell was developed to measure the high pressure phase behavior of gas + aqueous salt solutions and validated through the measurement, and comparison against literature data, of two systems, the H2O + CO2 and H2O + CO2 + NaCl, at temperatures up to 363 K and pressures up to 13 MPa. As previously reported by others, a salting out effect on the carbon dioxide solubility in water by NaCl is observed, decreasing its solubility as the salt concentration increases. Electrolyte versions of the cubic-plus-association and the RKSA-Infochem equations of state were used to estimate the H2O + CO2 and H2O + CO2 + NaCl phase behavior, with both EoS providing a good representation of the experimental data.

  • Journal LogoThermophysical Properties of Phosphonium-based Ionic Liquids
    Fluid Phase Equilibria 400 (2015) 103-113  doi10.1016/j.fluid.2015.05.009

    Experimental data for density, viscosity, refractive index and surface tension of four phosphonium-based ionic liquids were measured in the temperature range between (288.15 and 353.15) K and at atmospheric pressure. The ionic liquids considered include tri(isobutyl) methylphosphonium tosylate, [Pi(444)1][Tos], tri(butyl) methylphosphonium methylsulfate, [P4441][CH3SO4], tri(butyl) ethylphosphonium diethylphosphate, [P4442][(C2H5O)2PO2], and tetraoctylphosphonium bromide, [P8888][Br]. Additionally, derivative properties, such as the isobaric thermal expansion coefficient, the surface thermodynamic properties and the critical temperatures for the investigated ionic liquids were also estimated and are presented and discussed. Group contribution methods were evaluated and fitted to the density, viscosity and refractive index experimental data.

  • Journal LogoVapor-Liquid Equilibria of Imidazolium Ionic Liquids with Cyano Containing Anions with Water and Ethanol
    The Journal of Physical Chemistry B 119 (2015) 10287-10303  doi10.1021/acs.jpcb.5b03324

    Isobaric vapor–liquid equilibria of 1-butyl-3-methylimidazolium thiocyanate ([C4C1im][SCN]), 1-butyl-3-methylimidazolium dicyanamide ([C4C1im][N(CN)2]), 1-butyl-3-methylimidazolium tricyanomethanide ([C4C1im][C(CN)3]), and 1-ethyl-3-methylimidazolium tetracyanoborate ([C2C1im][B(CN)4]), with water and ethanol were measured over the whole concentration range at 0.1, 0.07, and 0.05 MPa. Activity coefficients were estimated from the boiling temperatures of the binary systems, and the data were used to evaluate the ability of COSMO-RS for describing these molecular systems. Aiming at further understanding the molecular interactions on these systems, molecular dynamics (MD) simulations were performed. On the basis of the interpretation of the radial and spatial distribution functions along with coordination numbers obtained through MD simulations, the effect of the increase of CN-groups in the IL anion in its capability to establish hydrogen bonds with water and ethanol was evaluated. The results obtained suggest that, for both water and ethanol systems, the anion [N(CN)2]− presents the higher ability to establish favorable interactions due to its charge, and that the ability of the anions to interact with the solvent, decreases with further increasing of the number of cyano groups in the anion. The ordering of the partial charges in the nitrogen atoms from the CN-groups in the anions agrees with the ordering obtained for VLE and activity coefficient data.

  • Journal LogoThermophysical Properties of Glycols and Glymes
    The Journal of Chemical & Engineering Data (2015)  doi10.1021/acs.jced.5b00662

    Experimental data for density, viscosity, refractive index and sound speed of 11 glycols and glymes were measured in the temperature range between (283.15 and 373.15) K and at atmospheric pressure. The compounds evaluated include ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TriEG), tetraethylene glycol (TeEG), ethylene glycol ethyl ether (EGEE), diethylene glycol methyl ether (DEGME), diethylene glycol dimethyl ether (DEGDME), diethylene glycol ethyl ether (DEGEE), diethylene glycol diethyl ether (DEGDEE), triethylene glycol dimethyl ether (TriEGDME), and tetraethylene glycol dimethyl ether (TeEGDME). Additionally, derivative properties, such isobaric thermal expansion coefficient and isentropic compressibilities were also estimated and discussed. The compounds evaluated were selected to evaluate the impact of molecular structure changes on their thermophysical properties. Effects like the increase in the number of ethoxy groups, shown to lead to an increase of the density, molar volume, viscosity, and refractive index, or the loss of the hydroxyl groups through the substitution of the hydroxyl groups hydrogen by a methyl or ethyl group, shown to lead to a significant decrease on the density, viscosity, and sound speed, are evaluated and discussed.

  • Journal LogoHigh Pressure Solubility of CH4, N2O and N2 in 1-butyl-3-methylimidazolium dicyanamide: Solubilities, Selectivities and soft-SAFT Modeling
    The Journal of Supercritical Fluids 110 (2016) 56-64  doi10.1016/j.supflu.2015.12.006

    The society and industry commitment to progressively reduce Green House Gases (GHGs) emissions forged important challenges that conventional gas separation processes are unable to overcome. Ionic liquids (ILs) have been attracting an outstanding attention during the last decade as a promising class of viable solvents to capture pollutants and for gas separation processes. Being the IL-based membranes gas separation controlled by the gas solubility in the IL rather than by its diffusivity, the solubility of gases in ILs stands as highly relevant input for their application in liquid membranes. As part of a continuing effort to develop an IL based process for high pressure capture of GHGs, the phase equilibria of nitrous oxide (N2O), methane (CH4) and nitrogen (N2) were investigated in this work. Experimental gas–liquid equilibrium data for N2O, CH4 and N2 in [C4C1im][N(CN)2] were determined in the (293 to 363) K temperature range, for pressures up to 70 MPa and gas mole fractions up to 35 %.
    Unfavorable interactions towards the studied gases, with positive deviations to ideality, were observed for all the studied gases, placing the studied IL among those with the lowest selectivities reported. The observed behavior highlights that a delicate balance between the solvent polarity and its molar volume must be ascertained when a highly selective solvent for N2 or CH4 separation is envisaged. The soft-SAFT EoS successfully described the high pressure phase behavior data using the molecular model and parameters sets reported in previous works. A good description of the binary systems studied, including the small CH4 temperature dependency and the N2 reverse temperature dependency on the solubility were achieved using just one binary interaction parameter. This reinforces the use of soft-SAFT as an accurate model to describe the behavior of gases in ILs for different applications.

  • Journal LogoDispelling Some Myths About the CO2 Solubility in Ionic Liquids
    Physical Chemistry Chemical Physics (2016)  doi10.1039/C6CP01896C

    Ionic liquids have been objects of extensive research for physical sorption of CO2 and a number of myths have been perpetuated in the literature, for lack of a critical analysis, concerning their potential for CO2 capture. This study carries a critical analysis of a number of widely accepted ideas and others not so well accepted that have been repeatedly expressed in the literature concerning the CO2 physical sorption in ionic liquids. Using the CO2 solubility in eicosane as benchmark, it will be shown that there is no evidence that ILs display a physical sorption of CO2 larger than n-alkanes when analyzed in adequate concentration units; the fluorination of the ions has no impact on the CO2 solubility and the oxygenation will marginally contribute to a decrease of the solubility. Ionic liquid-based deep eutectic systems are also shown to have a poor CO2 solubility. Although these widely used approaches to physically enhance the CO2 solubility in ILs do not seem to have any positive influence, this does not mean that other types of interaction cannot provide enhanced CO2 solubility as in the case of the anion [B(CN)4] confirmed here by a critical analysis of the published data. The mechanism of CO2 physical sorption in ionic liquids is discussed based on the results analyzed, supported by spectroscopic measurements and molecular simulations previously reported and further suggestions of possibilities for enhanced physical sorption based on fluorinated aromatic rings, other cyano based anions, mixtures with other ILs or solvents or the use of porous liquids are proposed.

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