Multiphase equilibrium in mixtures of [C(4)mim][PF6] with supercritical carbon dioxide, water, and ethanol: Applications in catalysis

The ionic liquid [C(4)mim][PF6] and supercritical carbon dioxide produce multiphase systems when mixed with ethanol and water. Mixtures of these four solvents can be made to go, by small changes in composition, through a succession of phase changes, involving one, two and three-phase situations. Increasing carbon dioxide pressure induces first the appearance of an intermediate liquid phase and later the merging of this phase with the gas, leaving all the ionic liquid in a separate, denser liquid. This succession is suitable to carry out reaction cycles in ionic liquid-based solvents, with complete recovery of the reaction product by CO2 decompression

Phase behaviour of room temperature ionic liquid solutions: an unusually large co-solvent effect in (water plus ethanol)

A surprising mixed solvent effect, both in its magnitude and direction, has been found in the phase diagram of the ternary mixture of ([C4mim][PF6]+(water+ethanol)). For a molar ratio of 1∶1 of water to ethanol, the co-solvent effect in the near-critical demixing temperature can be as large as 80 K

Pressure, isotope, and water co-solvent effects in liquid-liquid equilibria of (ionic liquid plus alcohol) systems

Liquid-liquid phase splitting in ternary mixtures that contain a room-temperature ionic liquid and an alcohol aqueous solution-namely, [bmim] [PF6] + ethanol + water and [bmim] [NTf2] + 2-methylpropanol + water-is studied. Experimental cloud-point temperatures were obtained up to pressures of 400 bar, using a He-Ne laser light-scattering technique. Although pressurization favors mutual miscibility in the presence of high concentrations of alcohols, the contrary occurs in water-rich solutions. Both ternary mixtures exhibit a very pronounced water-alcohol co-solvent effect. Solvent isotope effects are also investigated. Phase diagrams are discussed using a phenomenological approach based on a "polymer-like" G(E) model coupled with the statistical-mechanical theory of isotope effects. The combined effect of a red shift of -15 cm(-1) for the O-H deformation mode of ethanol with a blue shift of +35 cm(-1) for the O-H stretching mode, both of which occurring after liquid infinite dilution in the ionic liquid, rationalizes the observed isotope effect in the phase diagram. Predicted excess enthalpy (H-E) values are inferred from the model parameters. Furthermore, using the Prigogine-Defay equation, an estimation of the excess volumes (V-E) is obtained

A detailed thermodynamic analysis of [C(4)mim][BF4] plus water as a case study to model ionic liquid aqueous solutions

Since determining experimentally a wide variety of thermophysical properties - even for a very small portion of the already known room temperature ionic liquids ( and their mixtures and solutions) - is an impossible goal, it is imperative that reliable predictive methods be developed. In turn, these methods might offer us clues to understanding the underlying ion - ion and ion - molecule interactions. 1-Butyl-3-methylimidazolium tetrafluoroborate, one of the most thoroughly investigated ionic liquids, together with water, the greenest of the solvents, have been chosen in this work in order to use their mixtures as a case study to model other, greener, ionic liquid aqueous solutions. We focus our attention both on very simple methodologies that permit one to calculate accurately the mixture's molar volumes and heat capacities as well as more sophisticated theories to predict excess properties, pressure and isotope effects in the phase diagrams, and anomalies in some response functions to criticality, with a minimum of information. In regard to experimental work, we have determined: ( a) densities as a function of temperature (278.15 <T/ K <333.15), pressure ( 1 <p/bar <600), and composition (0 <x(IL) <1), thus also excess molar volumes; (b) heat capacities and excess molar enthalpies as a function of temperature ( 278.15 <T/ K <333.15) and composition ( 0 <xIL <1); and ( c) liquid - liquid phase diagrams and their pressure ( 1 <p/ bar <700) and isotopic (H2O/D2O) dependences. The evolution of some of the aforementioned properties in their approach to the critical region has deserved particular attention

Phase behavior and thermodynamic properties of ionic liquids, ionic liquid mixtures, and ionic liquid solutions

An overview of experimental and theoretical studies recently performed in the Oeiras/Lisbon laboratories is provided. Typical showcase examples of UCST demixing of ionic liquid solutions are presented and discussed. Co-solvency, pressure, and isotope effects were investigated. In order to rationalize the observed effects, a phenomenological g(E)-model was successfully applied, which permitted us to establish strong links between phase behavior and excess properties. Speed of propagation of ultrasound waves and densities in pure ILs as a function of temperature and pressure were determined from which several other thermodynamic properties such as compressibilities, expansivities and heat capacities, were derived. The quasi-ideality of mixtures of ILs, as judged by the small values of their excess volumes, could have been predicted by the master linear representation of their pure liquid volumes as the size of either the cation or the anion change. Research has been carried out at a broad range of pressures, typically up to 1600 bar, sometimes inside the metastable liquid region. The current study focuses on [C(n)mim][PF6], [C(n)mim][NTf2], and [C(n)mim][BF4] where n is usually 4, but generally 2 <n <10