Ana Soto

Bis{(trifluoromethyl)sulfonyl}amide ionic liquids as solvents for the extraction of aromatic hydrocarbons from their mixtures with alkanes: effect of the nature of the cation

The liquid–liquid equilibria of two ternary systems comprising hexane, benzene and a bis{(trifluoromethyl)sulfonyl}amide ionic liquid, [A][NTf2] (where A = cation), have been determined at 40 °C. Specifically, the cations of the ionic liquids investigated are 1-ethylpyridinium, [C2py]+, and (2-hydroxyethyl)trimethylammonium, [N1 1 1(C2OH)]+. The effectiveness of each ionic liquid as solvent for the separation of benzene from its mixtures with hexane was evaluated, and compared to that of 1-ethyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide, [C2mim][NTf2], as well as of trihexyl(tetradecyl)phosphonium bis{(trifluoromethyl)sulfonyl}amide, [P6 6 6 14][NTf2]. It was observed that the ammonium ionic liquid leads to higher selectivities in a certain range of global compositions, but it presents lower distribution ratios. No significant difference was observed between the pyridinium and the imidazolium ionic liquids. It was concluded that these ionic liquids can be envisioned as potential alternatives for the replacement of conventional organic solvents currently used for the separation of aromatic and aliphatic hydrocarbons. The liquid–liquid equilibrium data were acceptably correlated by means of the ‘Non-Random Two-Liquid’ (NRTL) equation.

Apparent molar volume, isentropic compressibility, refractive index, and viscosity of DL-alanine in aqueous NaCl solutions

New experimental data at 25°C for the density, velocity of sound, refractive index, and viscosity of aqueous solutions of DL-alanine and NaCl are reported. The apparent molar volume and isentropic compressibility of DL-alanine in aqueous electrolyte solutions have been calculated from the measured properties. The results show that DL-alanine exhibits a positive volume transfer to solutions of a higher NaCl concentration and a negative apparent isentropic compressibility for DL-alanine in the presence of NaCl. These effects indicate that the apparent volume of DL-alanine is larger in solutions with higher electrolyte concentration and the water molecules surrounding the DL-alanine molecules are less compressible than the water molecules in the bulk solution. The results also show an increase in the viscosity of the solution with an increase in both DL-alanine and NaCl concentrations. These effects are attributed to the two charged groups of DL-alanine and the interactions between the charged groups and the hydrocarbon backbone of DL-alanine with the ions. A model, consisting of a short-range interaction term represented by a virial expansion and a Debye-Hückel term that considers long-range interactions, has been developed to correlate the measured experimental data.

Thermodynamics of Diglycine and Triglycine in Aqueous NaCl Solutions: Apparent Molar Volume, Isentropic Compressibility, and Refractive Index

New experimental data for the density, speed of sound, and refractive index of aqueous solutions of diglycine + NaCl and triglycine + NaCl have been reported. The apparent molar volume and apparent molar isentropic compressibility of these peptides at various NaCl concentrations have been calculated from the measured properties. The results show that both peptides exhibit a positive volume transfer to solutions with higher NaCl concentrations and a negative apparent isentropic compressibility in the presence of NaCl. These effects indicate that the apparent volumes of the peptide molecules are larger in solutions with higher NaCl concentrations and that the water molecules around the peptide molecules are less compressible than the water molecules in the bulk solvent. These effects are attributed to the doubly charged nature of the peptides and the interactions between the charged groups and hydrocarbon backbone of peptides with the ions.

Use of a green and cheap ionic liquid to purify gasoline octane boosters

This work demonstrates the ability of the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO4]) to act as an extraction solvent for liquid–liquid extraction and as an azeotrope breaker for extractive distillation, to separate the azeotropic mixture ethyl tert-butyl ether (ETBE) + ethanol, thus purifying the tertiary ether, which is the most used additive to improve the octane index of gasolines. To assess the suitability of [emim][EtSO4] to perform the mentioned separation, the liquid–liquid equilibrium (LLE) at 298.1 K and the isobaric vapour–liquid equilibrium (VLE) at 101.3 kPa have been determined for the ternary system ETBE + ethanol + [emim][EtSO4]. The separation sequence for the extractive distillation has been obtained from the residue curve map and checked by simulation. The equilibrium data have been adequately correlated by means of the NRTL equation, thus facilitating their computerized treatment.

Experimental data and modelling of apparent molar volumes, isentropic compressibilities and refractive indices in aqueous solutions of glycine + NaCl.

Experiments have been performed at 298.15 K to measure the density, sound velocity and refractive index of glycine in aqueous solutions of NaCl over a wide range of both glycine and NaCl concentrations. The values of apparent molar volume and isentropic compressibility of glycine were calculated from the measured data. The results show a positive transfer volume of glycine from an NaCl solution to a more concentrated NaCl solution. This indicates that the size of a glycine molecule is larger in a solution with higher NaCl concentration. The negative values of apparent isentropic compressibility imply that the water molecules around the glycine molecules are less compressible than the water molecules in the bulk solution. These effects are attributed to the doubly charged behaviour of glycine and to the formation of physically bonded ion-pairs between the charged groups of glycine and sodium and chloride ions. The formation of ion-pairs, whose extents of binding reactions depend on the concentrations of both NaCl and glycine, alter the hydration number of glycine. This also explains the reason for the increase in the size of glycine with an increase in the NaCl concentration. A model based on the Pitzer formalism has been developed to correlate the activity coefficient, apparent molar volume and isentropic compressibility of glycine in aqueous solutions of NaCl. The results show that the model can accurately correlate the interactions in aqueous solutions of glycine and NaCl.

Physical and equilibrium properties of diisopropyl ether+isopropyl alcohol+water system

Abstract Molar volume, isentropic compressibility, and molar refraction changes of mixing of the system diisopropyl ether (DIPE)+isopropyl alcohol (IPA)+water were determined at 298.15 K. These deviational properties were satisfactorily correlated with the composition data by means of Redlich–Kister polynomials. Tie line data have been determined at 298.15, 308.15, and 318.15 K for the ternary liquid–liquid equilibria, and were adequately correlated by means of the NRTL and UNIQUAC equation, and compared with results predicted by the UNIFAC method.

Effect of the cation and the anion of an electrolyte on the solubility of dl-aminobutyric acid in aqueous solutions: measurement and modelling

The solubilities at 298.2 K of dl-aminobutyric acid in aqueous solutions of NaCl, KCl, NaNO(3) and KNO(3) were measured. The solubility of DL-aminobutyric acid was found to be influenced by the concentration and by the nature of both the cation and the anion of the electrolyte. Comparison of the results obtained in this study and those for other amino acids reported in the literature, indicates that the structure of the hydrocarbon backbone of an amino acid plays an important role in the interactions of an amino acid with an electrolyte. A thermodynamic model has been used to correlate the solubilities of DL-aminobutyric acid in aqueous electrolyte solutions. The activity coefficients of the amino acid in the electrolyte solutions, were represented by a model proposed by Khoshkbarchi and Vera [M.K. Khoshkbarchi, J.H. Vera, AIChE J. 42 (1996) 2354; M.K. Khoshkbarchi, J.H. Vera, Ind. Eng. Chem. Res. 35 (1996) 4755]. This model, which considers a combination of both long- and short-range interactions, contains only two adjustable parameters. All other parameters are available in the literature. The model can accurately correlate the solubility of dl-aminobutyric acid in aqueous solutions of electrolytes.

VLE for water + ethanol + 1-octanol mixtures. Experimental measurements and correlations

Abstract Molar excess Gibbs free energies ( G E RT ) for the ternary system water + ethanol + 1-octanol were evaluated from the corresponding isobaric (101.32 kPa) vapour-liquid equilibrium data. The ( G E RT - composition data were then correlated by means of the Redlich-Kister polynomial and the NRTL and UNIQUAC equations, using an optimized value of 5.50 for the q′ UNIQUAC area parameter of 1-octanol. The experimental data were compared with data predicted using the ASOG, UNIFAC and UNIFAC-Lyngby group contribution methods.

Effect of cation and anion of an electrolyte on apparent molar volume, isentropic compressibility and refractive index of glycine in aqueous solutions.

Experiments at 298.15 K have been performed to measure the density, velocity of sound and refractive index in three water+glycine+electrolyte systems. The electrolytes studied were KCl, KNO3 and NaNO3. The values of apparent molar volume and isentropic compressibility of glycine in aqueous electrolyte solutions were calculated from the measured data. The results obtained in this study and those reported previously for water+glycine+NaCl system have been comparatively studied. The results show that the nature of both the cation and the anion of an electrolyte influence the behaviour of glycine in aqueous solutions. For all four electrolytes studied, the comparison shows a positive volume transfer for glycine from an electrolyte solution to a more concentrated solution of the same electrolyte. The results also show a negative apparent isentropic compressibility for glycine in the presence of the electrolytes studied. These effects indicate that the volume of a glycine molecule is larger in solutions with higher electrolyte concentration and the water molecules around the glycine molecules are less compressible than the water molecules in the bulk solution. These effects were attributed to the doubly charged behaviour of glycine and to the formation of physically bonded ion-pairs between the charged groups of glycine and the cation and the anion of the electrolyte.

Measurements and modelling of the solubility of a mixture of two amino acids in aqueous solutions

Abstract Measurements were performed to determine the solubilities at 298.2 K of two pairs of amino acids in aqueous solutions. The systems studied were water+glycine+ dl -aspartic acid and water+glycine+ dl -phenylalanine. The results show that for these systems the solubility of an amino acid increases as the concentration of the other amino acid increases. The solubility of dl -phenylalanine passes through a maximum with an increase in the glycine concentration. Comparison of the results obtained in this work with those reported in previous studies, indicates that the solubility of an amino acid in the presence of another amino acid depends not only on the concentration of the second amino acid, but also on the chemical structure of both amino acids. A model has been developed to correlate the solubilities of an amino acid in aqueous solutions of another amino acid. The activity coefficients of the amino acids, required to correlate the solubility were represented by two different models. An NRTL and a perturbed hard sphere model, with two amino acid–amino acid adjustable interaction parameters, were used. The water–amino acid interaction parameters in the NRTL model for the amino acids with low solubilities, namely dl -aspartic acid and dl -phenylalanine, were set to zero. Both activity models can accurately correlate the solubility of an amino acid in aqueous solutions of another amino acid. It was found that, at amino acid concentrations higher than the saturation in pure water, the NRTL model can extrapolate the activity coefficients of amino acids better than the perturbed hard sphere model.