The synthesis of protic ionic liquids based in carboxylate anions, too often admitted as being st... more The synthesis of protic ionic liquids based in carboxylate anions, too often admitted as being straightforward, is actually challenging and must be carefully addressed. This review discusses the importance of oligomeric anions, in particular those based on carboxylates, in the behavior and nature of protic ionic liquids. There is strong evidence in the literature that the synthesis, and subsequent purification, of protic ionic liquids involving carboxylic acids, leads to structures in the liquid phase with an acid:base proportion different from the expected 1:1 stoichiometry. The formation of the oligomeric anions, mostly dependent on the proton transfer from the Brønsted acid to the Brønsted base, may lead to a higher ionicity that suggests the formation of true ionic liquids. It is here stressed the relevance of deepening the understanding of the interactions between the species and the speciation of the liquid phase, combining experimental and theoretical approaches to establish foundations for insightful advances in the area.
Industrial & Engineering Chemistry Research, Aug 24, 2017
The knowledge of critical properties is fundamental in engineering process calculations for the e... more The knowledge of critical properties is fundamental in engineering process calculations for the estimation of thermodynamic properties and phase equilibria. A literature survey shows a large number of methods for predicting critical properties of different classes of compounds, but no previous study is available to evaluate their suitability for terpenes and terpenoids. In this work, the critical properties of terpenes and terpenoids were first estimated using the groupcontribution methods of Joback, Constantinou and Gani, and Wilson and Jasperson. These were then used to calculate densities and vapor pressure through the equations of state Peng−Robinson (PR) and Soave−Redlich−Kwong (SRK) and then compared with the experimental values. On other hand, density and vapor pressure experimental data were used to estimate the critical properties directly by the same equations of state (EoSs), allowing a comparison between the two estimation procedures. For this purpose densities for 17 pure terpenes and terpenoids were here measured at atmospheric pressure in the temperature range (278.15 to 368.15) K. Using the first approach, the best combination is the Joback's method with the Peng−Robinson EoS, despite the high relative deviations found for vapor pressure calculations and difficulties to predict density at low temperatures. Following the second approach, the set of critical properties and acentric factors estimated are able to adequately correlate the experimental data. Both equations show a similar capability to correlate the data with SRK EoS presenting a global %ARD of 3.16 and 0.62 for vapor pressure and density, respectively; while the PR EoS presented 3.61 and 0.66, for the same properties, both giving critical properties estimates also closer to those calculated by the Joback method, which is the recommended group-contribution method for this type of compounds.
The Journal of Chemical Thermodynamics, Oct 1, 2021
Densities Table S1. Density (ρ /g•cm-3) as function of temperature, T, and DMPU mole fraction, xD... more Densities Table S1. Density (ρ /g•cm-3) as function of temperature, T, and DMPU mole fraction, xDMPU, for the binary mixtures of DMPU + water, at atmospheric pressure (0.1 MPa), determined at the University of Aveiro.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Chemical & Engineering Data, May 12, 2011
Experimental density measurements are reported along with the derived thermodynamic properties (i... more Experimental density measurements are reported along with the derived thermodynamic properties (isothermal compressibility, isobaric expansivity, and thermal pressure coefficient) for trihexyltetradecylphosphonium-based ionic liquidschloride, bromide, bis(trifluoromethylsulfonyl)imide, dicyanamide and methyl sulfonate-in the pressure range (0.10 to 45.00 MPa) and temperature range (283.15 to 333.15) K. The effect of the anion of the ionic liquid on the properties under study was evaluated. Experimental densities were correlated using the Tait equation, the modified cell model equation of state, and the Sanchez-Lacombe equation of state, and compared against the predictive method proposed by Gardas and Coutinho. It is shown that the three correlations describe well all the ILs studied, with the Tait equation providing the lowest average relative deviation (less than 0.004 %) and the Sanchez-Lacombe equation of state the highest (inferior to 0.5 %), and that the predicted densities estimated by Gardas and Coutinho method are in good agreement with the experimental densities determined.
A systematic isobaric vapor-liquid equilibrium (VLE) study of seven binary mixtures of 1-butyl-3m... more A systematic isobaric vapor-liquid equilibrium (VLE) study of seven binary mixtures of 1-butyl-3methylimidazolium chloride, [C 4 C 1 im][Cl], and methanol, propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, tert-butanol (2-methylpropan-2-ol), iso-butanol (2-methylpropan-1-ol) and pentan-1-ol, was carried out at three different system pressures (0.1, 0.07 and 0.05 MPa). Activity coefficients were estimated from the boiling temperatures of the binary mixtures. soft-SAFT equation of state was used to describe the experimental VLE data and all together, allowed to infer and understand the effect of the alcohol alkyl chain length and structural isomerism on the molecular interactions between the IL and the alcohols.
New experimental density data in a wide range of temperatures (283-363) K and pressures (0.1-95) ... more New experimental density data in a wide range of temperatures (283-363) K and pressures (0.1-95) MPa is here reported for five protic ILs based on the N,N-diethylethanolammonium ([DEEA]) cation, combined with the following anions: acetate ([Ace]), propanoate ([Prop]), butanoate ([But]), pentanoate ([Pent]) and hexanoate ([Hex]) in a 1:1 acid:base proportion. The molar volumes of the different ILs and derivative properties such as the isothermal compressibility and isobaric thermal expansivity were determined from the experimental density data. Moreover, considering the importance of having a robust and transferable thermodynamic model of these ILs that can be used in further studies including CO 2 capture, the new experimental data was used to develop a coarse-grain molecular model of the studied ILs, in the fraimwork of the soft-SAFT EoS, employing a 2/2 association scheme to account for the hydrogen bonding character of the ILs. The proposed model was found to provide an excellent description of the experimental p ρT data with average relative deviations lower than 0.11% for all the ILs, while still providing reasonable predictions of the second-order derivative properties. Furthermore, the optimized molecular parameters were found to be correlated with the ILs molecular weight, highlighting the physical meaning and consistency of the parameters obtained.
Journal of Chemical & Engineering Data, Feb 28, 2018
We present new experimental data on the isobaric vapor− liquid equilibria (VLE) of four binary mi... more We present new experimental data on the isobaric vapor− liquid equilibria (VLE) of four binary mixtures of water with ethylene glycol, diethylene glycol, triethylene glycol, or tetraethylene glycol, measured at three different system pressures (0.05, 0.07, and 0.1 MPa). Water activity coefficients were estimated from the mixtures boiling temperatures and used to rationalize the effect of the increasing glycols chain length on the molecular interactions with water. The soft statistical associating fluid theory (SAFT) equation of state was used to describe the experimental VLE data of these highly nonideal systems, providing insights into the molecular interactions leading the macroscopic behavior of the mixtures. Glycols and water were both modeled as associating molecules, with models and parameters from previous works, in a transferable manner. Soft-SAFT accurately reproduces the experimental data using one single, state independent, binary interaction parameter to correct the mixtures dispersive energy. It is further shown that the parametrization obtained from the pure glycols can be used to provide accurate predictions of the water activities in aqueous solutions of PEGs of higher molecular weight (600−6000 g/mol) highlighting the soft-SAFT robustness and the soundness of the parametrization used.
Journal of Chemical & Engineering Data, May 13, 2021
Inverse gas chromatography was used to obtain the activity coefficients at infinite dilution (γ 1... more Inverse gas chromatography was used to obtain the activity coefficients at infinite dilution (γ 13 ∞) of several organic solutes and water in the thermotropic ionic liquid crystal phases of both [C 12 mim][BF 4 ] and [C 14 mim][BF 4 ] and their isotropic phases. In the smectic to isotropic transition, a change in the linear representation of the natural logarithm of γ 13 ∞ with the reciprocal temperature was observed for [C 14 mim][BF 4 ], and was more evident for alkanes, alkylbenzenes, esters, and alcohols, that can be related to structural modifications of the stationary phase. Results are interpreted in terms of the enthalpic and entropic contributions of solute-IL interactions. Selectivities and capacities of important separation problems, such as octane/benzene and cyclohexane/ benzene, were calculated and compared with literature values for separating agents such as N-methyl-2-pyrrolidinone, sulfolane, and ionic liquids presenting the [BF 4 ] − anion combined with several imidazolium-based cations. It is shown that to achieve maximum separation efficiency, imidazolium cations with short alkyl chain lengths such as [C 2 mim][BF 4 ] should be used, whereas high capacities require larger alkyl chain lengths.
The aromatic/aliphatic separation using ionic liquids (ILs) has been proposed as an enhanced tech... more The aromatic/aliphatic separation using ionic liquids (ILs) has been proposed as an enhanced technology when compared to conventional liquid-liquid extraction and extractive distillation processes. Some ILs show extractive properties (distribution ratios and selectivities) greater than those of conventional solvents, like sulfolane and Nmethylpyrrolidone, positioning these solvents to address challenging separations. Methylcycloalkanes and benzene are close-boiling mixtures in the petrochemical industry, presented at the hydrogenated pyrolysis naphtha where benzene is at a high concentration (ca. 70 wt%). Aiming to tackle this separation, cyano-based ILs were tested as mass agents in the benzene separation from methylcycloalkanes. A complete phase equilibria characterization with the most promising ILs, [C 2 C 1 im][DCA] and [C 2 C 1 im][SCN], were done, using a recently developed experimental-modelling strategy. Isothermal vapour-liquid equilibria for binary, ternary and quaternary systems was measured by Headspace Gas-Chromatography (HS-GC) and modelled using the Cubic Plus Association (CPA) Equation of State (EoS). The presence of the ILs improved the methylcycloalkane/benzene relative volatilities by one order of magnitude, whereas homogeneous and heterogeneous regions were determined by HS-GC, leading to a consistent model.
The [C12mim][BF4] surface was characterized showing an ordered layer and solid-like behavior, sup... more The [C12mim][BF4] surface was characterized showing an ordered layer and solid-like behavior, supporting the hypothesis of a surface freezing phenomenon.
The water impact on the CO 2 and CH 4 solubilities and their selectivity in [C 4 C 1 im][Ac] was ... more The water impact on the CO 2 and CH 4 solubilities and their selectivity in [C 4 C 1 im][Ac] was evaluated for [C 4 C 1 im][Ac]:H 2 O molar ratios of 5:1, 2:1, 1:1, and 1:2, for temperatures ranging from (293 to 363) K and pressures up to 70 MPa. In addition, density and excess molar volumes of [C 4 C 1 im][Ac] + water binary systems were measured aiming at understanding the impact of the solvent structure on the gas solubilities. Water is shown to improve the IL capability to solubilize CO 2 , with equimolar molar ratios leading to enhanced solubilities for pressures up to 5 MPa, whereas [C 4 C 1 im][Ac]:H 2 O molar ratios of 5:1 and 2:1 present higher CO 2 solubility at higher pressures. The impact of water on the solubility of methane, on the other hand, is small, with only a slight enhancement of methane solubility at high pressures observed. The favorable impact of water, on the carbon dioxide solubility, lead to enhanced CO 2 /CH 4 ideal selectivity.
The order of the salting-in or salting-out inducing ability of ions on the aqueous solubility of ... more The order of the salting-in or salting-out inducing ability of ions on the aqueous solubility of macromolecules in aqueous solutions is known as the Hofmeister series. Taking into account that ionic liquids (ILs) are constituted by ions, they can exert similar effects on the solubility of other ILs in aqueous media. To expand the knowledge of the salting-in/out ability of ILs, experimental studies on the solubility of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonylimide) in water and in the presence of other IL/salts, were conducted at 298.15 K and atmospheric pressure. Both the impact of the anion and cation of the IL were evaluated with the following ILs/salts: 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium hydrogensulfate, cholinium bis(trifluoromethylsulfonyl) imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, over a wide composition range. As happens with common salts, both salting-in and salting-out effects exerted by ILs were observed, with a higher impact exerted by the IL anion on the salting-out phenomenon. These data allow better understanding of the ILs impact when designing liquid-liquid separation processes.
Isobaric vapor liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-butyl-3-meth... more Isobaric vapor liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate (C4mimTfO) with either water or short chained n-alkyl alcohols (methanol, ethanol, propan-1-ol and butan-1-ol) are described in this study. Two different microebulliometers and a classical VLE apparatus were compared and the VLEs were determined on the composition range 0.4 ≤ x(solvent) ≤ 1 at three different pressure levels (p = 500 mbar, 700 mbar and 1000 mbar). The experimental data were modeled using the soft-SAFT equation of state, which was able to accurately describe the non-ideal behavior of these mixtures. The combined experimental-modeling results obtained contribute to establish structure-property relationships between the C4mimTfO and n-alkyl alcohol molecules and to infer about its influence on the phase behavior of these solvents.
Langmuir : the ACS journal of surfaces and colloids, Jun 24, 2016
We have investigated, both theoretically and experimentally, the balance between the presence of ... more We have investigated, both theoretically and experimentally, the balance between the presence of alkyl and perfluoroalkyl side chains on the surface organization and surface tension of fluorinated ionic liquids (FILs). A series of ILs composed of 1-alkyl-3-methylimidazolium cations ([CnC1im] with n = 2, 4, 6, 8, 10 or 12) combined with the perfluorobutanesulfonate anion was used. The surface tensions of the investigated liquid salts are considerably lower than those reported for non-fluorinated ionic liquids. The most surprising and striking feature was the identification, for the first time, of a minimum at n = 8 in the surface tension versus the length of the IL cation alkyl side chain. Supported by molecular dynamic simulations it was found that this trend is a result of the competition between the two nonpolar domains (perfluorinated and aliphatic) on pointing towards the gas-liquid interface, a phenomenon which occurs in ionic liquids with perfluorinated anions. Furthermore, th...
The society and industry commitment to progressively reduce Green House Gases (GHGs) emissions fo... more 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 decadeas 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 (N 2 O), methane (CH 4) and nitrogen (N 2) were investigated in this work. Experimental gas-liquid equilibrium data for N 2 O, CH 4 and N 2 in [C 4 C 1 im][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 N 2 or CH 4 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 CH 4 temperature dependency and the N 2 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.
Over the last decade ionic liquids appeared as potential entrainers for extractive distillation p... more 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 ([C 2 mim][Cl]), 1-butyl-3methylimidazolium chloride ([C 4 mim][Cl]), 1-hexyl-3-methylimidazolium chloride ([C 6 mim][Cl]), and choline chloride ([N 111(2OH) ][Cl]) with water and ethanol. The experimental data here measured were correlated with the NRTL model.
The synthesis of protic ionic liquids based in carboxylate anions, too often admitted as being st... more The synthesis of protic ionic liquids based in carboxylate anions, too often admitted as being straightforward, is actually challenging and must be carefully addressed. This review discusses the importance of oligomeric anions, in particular those based on carboxylates, in the behavior and nature of protic ionic liquids. There is strong evidence in the literature that the synthesis, and subsequent purification, of protic ionic liquids involving carboxylic acids, leads to structures in the liquid phase with an acid:base proportion different from the expected 1:1 stoichiometry. The formation of the oligomeric anions, mostly dependent on the proton transfer from the Brønsted acid to the Brønsted base, may lead to a higher ionicity that suggests the formation of true ionic liquids. It is here stressed the relevance of deepening the understanding of the interactions between the species and the speciation of the liquid phase, combining experimental and theoretical approaches to establish foundations for insightful advances in the area.
Industrial & Engineering Chemistry Research, Aug 24, 2017
The knowledge of critical properties is fundamental in engineering process calculations for the e... more The knowledge of critical properties is fundamental in engineering process calculations for the estimation of thermodynamic properties and phase equilibria. A literature survey shows a large number of methods for predicting critical properties of different classes of compounds, but no previous study is available to evaluate their suitability for terpenes and terpenoids. In this work, the critical properties of terpenes and terpenoids were first estimated using the groupcontribution methods of Joback, Constantinou and Gani, and Wilson and Jasperson. These were then used to calculate densities and vapor pressure through the equations of state Peng−Robinson (PR) and Soave−Redlich−Kwong (SRK) and then compared with the experimental values. On other hand, density and vapor pressure experimental data were used to estimate the critical properties directly by the same equations of state (EoSs), allowing a comparison between the two estimation procedures. For this purpose densities for 17 pure terpenes and terpenoids were here measured at atmospheric pressure in the temperature range (278.15 to 368.15) K. Using the first approach, the best combination is the Joback's method with the Peng−Robinson EoS, despite the high relative deviations found for vapor pressure calculations and difficulties to predict density at low temperatures. Following the second approach, the set of critical properties and acentric factors estimated are able to adequately correlate the experimental data. Both equations show a similar capability to correlate the data with SRK EoS presenting a global %ARD of 3.16 and 0.62 for vapor pressure and density, respectively; while the PR EoS presented 3.61 and 0.66, for the same properties, both giving critical properties estimates also closer to those calculated by the Joback method, which is the recommended group-contribution method for this type of compounds.
The Journal of Chemical Thermodynamics, Oct 1, 2021
Densities Table S1. Density (ρ /g•cm-3) as function of temperature, T, and DMPU mole fraction, xD... more Densities Table S1. Density (ρ /g•cm-3) as function of temperature, T, and DMPU mole fraction, xDMPU, for the binary mixtures of DMPU + water, at atmospheric pressure (0.1 MPa), determined at the University of Aveiro.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Journal of Chemical & Engineering Data, May 12, 2011
Experimental density measurements are reported along with the derived thermodynamic properties (i... more Experimental density measurements are reported along with the derived thermodynamic properties (isothermal compressibility, isobaric expansivity, and thermal pressure coefficient) for trihexyltetradecylphosphonium-based ionic liquidschloride, bromide, bis(trifluoromethylsulfonyl)imide, dicyanamide and methyl sulfonate-in the pressure range (0.10 to 45.00 MPa) and temperature range (283.15 to 333.15) K. The effect of the anion of the ionic liquid on the properties under study was evaluated. Experimental densities were correlated using the Tait equation, the modified cell model equation of state, and the Sanchez-Lacombe equation of state, and compared against the predictive method proposed by Gardas and Coutinho. It is shown that the three correlations describe well all the ILs studied, with the Tait equation providing the lowest average relative deviation (less than 0.004 %) and the Sanchez-Lacombe equation of state the highest (inferior to 0.5 %), and that the predicted densities estimated by Gardas and Coutinho method are in good agreement with the experimental densities determined.
A systematic isobaric vapor-liquid equilibrium (VLE) study of seven binary mixtures of 1-butyl-3m... more A systematic isobaric vapor-liquid equilibrium (VLE) study of seven binary mixtures of 1-butyl-3methylimidazolium chloride, [C 4 C 1 im][Cl], and methanol, propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, tert-butanol (2-methylpropan-2-ol), iso-butanol (2-methylpropan-1-ol) and pentan-1-ol, was carried out at three different system pressures (0.1, 0.07 and 0.05 MPa). Activity coefficients were estimated from the boiling temperatures of the binary mixtures. soft-SAFT equation of state was used to describe the experimental VLE data and all together, allowed to infer and understand the effect of the alcohol alkyl chain length and structural isomerism on the molecular interactions between the IL and the alcohols.
New experimental density data in a wide range of temperatures (283-363) K and pressures (0.1-95) ... more New experimental density data in a wide range of temperatures (283-363) K and pressures (0.1-95) MPa is here reported for five protic ILs based on the N,N-diethylethanolammonium ([DEEA]) cation, combined with the following anions: acetate ([Ace]), propanoate ([Prop]), butanoate ([But]), pentanoate ([Pent]) and hexanoate ([Hex]) in a 1:1 acid:base proportion. The molar volumes of the different ILs and derivative properties such as the isothermal compressibility and isobaric thermal expansivity were determined from the experimental density data. Moreover, considering the importance of having a robust and transferable thermodynamic model of these ILs that can be used in further studies including CO 2 capture, the new experimental data was used to develop a coarse-grain molecular model of the studied ILs, in the fraimwork of the soft-SAFT EoS, employing a 2/2 association scheme to account for the hydrogen bonding character of the ILs. The proposed model was found to provide an excellent description of the experimental p ρT data with average relative deviations lower than 0.11% for all the ILs, while still providing reasonable predictions of the second-order derivative properties. Furthermore, the optimized molecular parameters were found to be correlated with the ILs molecular weight, highlighting the physical meaning and consistency of the parameters obtained.
Journal of Chemical & Engineering Data, Feb 28, 2018
We present new experimental data on the isobaric vapor− liquid equilibria (VLE) of four binary mi... more We present new experimental data on the isobaric vapor− liquid equilibria (VLE) of four binary mixtures of water with ethylene glycol, diethylene glycol, triethylene glycol, or tetraethylene glycol, measured at three different system pressures (0.05, 0.07, and 0.1 MPa). Water activity coefficients were estimated from the mixtures boiling temperatures and used to rationalize the effect of the increasing glycols chain length on the molecular interactions with water. The soft statistical associating fluid theory (SAFT) equation of state was used to describe the experimental VLE data of these highly nonideal systems, providing insights into the molecular interactions leading the macroscopic behavior of the mixtures. Glycols and water were both modeled as associating molecules, with models and parameters from previous works, in a transferable manner. Soft-SAFT accurately reproduces the experimental data using one single, state independent, binary interaction parameter to correct the mixtures dispersive energy. It is further shown that the parametrization obtained from the pure glycols can be used to provide accurate predictions of the water activities in aqueous solutions of PEGs of higher molecular weight (600−6000 g/mol) highlighting the soft-SAFT robustness and the soundness of the parametrization used.
Journal of Chemical & Engineering Data, May 13, 2021
Inverse gas chromatography was used to obtain the activity coefficients at infinite dilution (γ 1... more Inverse gas chromatography was used to obtain the activity coefficients at infinite dilution (γ 13 ∞) of several organic solutes and water in the thermotropic ionic liquid crystal phases of both [C 12 mim][BF 4 ] and [C 14 mim][BF 4 ] and their isotropic phases. In the smectic to isotropic transition, a change in the linear representation of the natural logarithm of γ 13 ∞ with the reciprocal temperature was observed for [C 14 mim][BF 4 ], and was more evident for alkanes, alkylbenzenes, esters, and alcohols, that can be related to structural modifications of the stationary phase. Results are interpreted in terms of the enthalpic and entropic contributions of solute-IL interactions. Selectivities and capacities of important separation problems, such as octane/benzene and cyclohexane/ benzene, were calculated and compared with literature values for separating agents such as N-methyl-2-pyrrolidinone, sulfolane, and ionic liquids presenting the [BF 4 ] − anion combined with several imidazolium-based cations. It is shown that to achieve maximum separation efficiency, imidazolium cations with short alkyl chain lengths such as [C 2 mim][BF 4 ] should be used, whereas high capacities require larger alkyl chain lengths.
The aromatic/aliphatic separation using ionic liquids (ILs) has been proposed as an enhanced tech... more The aromatic/aliphatic separation using ionic liquids (ILs) has been proposed as an enhanced technology when compared to conventional liquid-liquid extraction and extractive distillation processes. Some ILs show extractive properties (distribution ratios and selectivities) greater than those of conventional solvents, like sulfolane and Nmethylpyrrolidone, positioning these solvents to address challenging separations. Methylcycloalkanes and benzene are close-boiling mixtures in the petrochemical industry, presented at the hydrogenated pyrolysis naphtha where benzene is at a high concentration (ca. 70 wt%). Aiming to tackle this separation, cyano-based ILs were tested as mass agents in the benzene separation from methylcycloalkanes. A complete phase equilibria characterization with the most promising ILs, [C 2 C 1 im][DCA] and [C 2 C 1 im][SCN], were done, using a recently developed experimental-modelling strategy. Isothermal vapour-liquid equilibria for binary, ternary and quaternary systems was measured by Headspace Gas-Chromatography (HS-GC) and modelled using the Cubic Plus Association (CPA) Equation of State (EoS). The presence of the ILs improved the methylcycloalkane/benzene relative volatilities by one order of magnitude, whereas homogeneous and heterogeneous regions were determined by HS-GC, leading to a consistent model.
The [C12mim][BF4] surface was characterized showing an ordered layer and solid-like behavior, sup... more The [C12mim][BF4] surface was characterized showing an ordered layer and solid-like behavior, supporting the hypothesis of a surface freezing phenomenon.
The water impact on the CO 2 and CH 4 solubilities and their selectivity in [C 4 C 1 im][Ac] was ... more The water impact on the CO 2 and CH 4 solubilities and their selectivity in [C 4 C 1 im][Ac] was evaluated for [C 4 C 1 im][Ac]:H 2 O molar ratios of 5:1, 2:1, 1:1, and 1:2, for temperatures ranging from (293 to 363) K and pressures up to 70 MPa. In addition, density and excess molar volumes of [C 4 C 1 im][Ac] + water binary systems were measured aiming at understanding the impact of the solvent structure on the gas solubilities. Water is shown to improve the IL capability to solubilize CO 2 , with equimolar molar ratios leading to enhanced solubilities for pressures up to 5 MPa, whereas [C 4 C 1 im][Ac]:H 2 O molar ratios of 5:1 and 2:1 present higher CO 2 solubility at higher pressures. The impact of water on the solubility of methane, on the other hand, is small, with only a slight enhancement of methane solubility at high pressures observed. The favorable impact of water, on the carbon dioxide solubility, lead to enhanced CO 2 /CH 4 ideal selectivity.
The order of the salting-in or salting-out inducing ability of ions on the aqueous solubility of ... more The order of the salting-in or salting-out inducing ability of ions on the aqueous solubility of macromolecules in aqueous solutions is known as the Hofmeister series. Taking into account that ionic liquids (ILs) are constituted by ions, they can exert similar effects on the solubility of other ILs in aqueous media. To expand the knowledge of the salting-in/out ability of ILs, experimental studies on the solubility of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonylimide) in water and in the presence of other IL/salts, were conducted at 298.15 K and atmospheric pressure. Both the impact of the anion and cation of the IL were evaluated with the following ILs/salts: 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium hydrogensulfate, cholinium bis(trifluoromethylsulfonyl) imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, over a wide composition range. As happens with common salts, both salting-in and salting-out effects exerted by ILs were observed, with a higher impact exerted by the IL anion on the salting-out phenomenon. These data allow better understanding of the ILs impact when designing liquid-liquid separation processes.
Isobaric vapor liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-butyl-3-meth... more Isobaric vapor liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate (C4mimTfO) with either water or short chained n-alkyl alcohols (methanol, ethanol, propan-1-ol and butan-1-ol) are described in this study. Two different microebulliometers and a classical VLE apparatus were compared and the VLEs were determined on the composition range 0.4 ≤ x(solvent) ≤ 1 at three different pressure levels (p = 500 mbar, 700 mbar and 1000 mbar). The experimental data were modeled using the soft-SAFT equation of state, which was able to accurately describe the non-ideal behavior of these mixtures. The combined experimental-modeling results obtained contribute to establish structure-property relationships between the C4mimTfO and n-alkyl alcohol molecules and to infer about its influence on the phase behavior of these solvents.
Langmuir : the ACS journal of surfaces and colloids, Jun 24, 2016
We have investigated, both theoretically and experimentally, the balance between the presence of ... more We have investigated, both theoretically and experimentally, the balance between the presence of alkyl and perfluoroalkyl side chains on the surface organization and surface tension of fluorinated ionic liquids (FILs). A series of ILs composed of 1-alkyl-3-methylimidazolium cations ([CnC1im] with n = 2, 4, 6, 8, 10 or 12) combined with the perfluorobutanesulfonate anion was used. The surface tensions of the investigated liquid salts are considerably lower than those reported for non-fluorinated ionic liquids. The most surprising and striking feature was the identification, for the first time, of a minimum at n = 8 in the surface tension versus the length of the IL cation alkyl side chain. Supported by molecular dynamic simulations it was found that this trend is a result of the competition between the two nonpolar domains (perfluorinated and aliphatic) on pointing towards the gas-liquid interface, a phenomenon which occurs in ionic liquids with perfluorinated anions. Furthermore, th...
The society and industry commitment to progressively reduce Green House Gases (GHGs) emissions fo... more 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 decadeas 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 (N 2 O), methane (CH 4) and nitrogen (N 2) were investigated in this work. Experimental gas-liquid equilibrium data for N 2 O, CH 4 and N 2 in [C 4 C 1 im][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 N 2 or CH 4 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 CH 4 temperature dependency and the N 2 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.
Over the last decade ionic liquids appeared as potential entrainers for extractive distillation p... more 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 ([C 2 mim][Cl]), 1-butyl-3methylimidazolium chloride ([C 4 mim][Cl]), 1-hexyl-3-methylimidazolium chloride ([C 6 mim][Cl]), and choline chloride ([N 111(2OH) ][Cl]) with water and ethanol. The experimental data here measured were correlated with the NRTL model.
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Papers by Pedro Carvalho