Henrique J. R. Guedes

Phase behaviour of room temperature ionic liquid solutions: an unusually large co-solvent effect in (water + 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.

Changing from an unusual high-temperature demixing to a UCST-type in mixtures of 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide and arenes

Upper critical solution temperature (UCST) combined with a high-temperature demixing type of phase diagrams are reported for binary liquid mixtures containing the ionic liquids, 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ([Cnmim][NTf2], where n = 2, 4, 6, 8, 10) and benzene, toluene, or α-methylstyrene (PhC(Me)CH2), at atmospheric and moderately high pressure. The phase diagrams were determined either using a dynamic method with visual detection of phase transitions or a laser light scattering technique. In our investigations, as the imidazolium alkyl chain length of the ionic liquid increases, the mixtures containing an arene evolve from a rarely found high-temperature demixing behaviour, to “hour-glass”, to the common phase splitting as temperature diminishes (UCST, whenever a critical point was found). For the three systems containing specifically [C10mim][NTf2] with benzene, toluene, or α-methylstyrene, data were also collected up to 5 MPa using a high-pressure laser light scattering apparatus. For all phase diagrams, the critical compositions correspond to low concentrations of the ionic liquid. This fact underlies the possibility that ionic liquids, even in relatively dilute solutions, tend to form multiple-ion aggregates. This was corroborated by electro-spray mass spectrometry.

Thermodynamic properties of liquid mixtures of carbon monoxide and methane

Abstract The equations of state of liquid methane at 125.00 K and of six liquid mixtures of carbon monoxide and methane at 116.30, 120.00 and 125.00 K have been measured from just above the saturation vapour pressure to the freezing pressure of methane. The results show that the excess volume VE is large and negative at low pressures but becomes less negative as the pressure is increased, being almost zero at the highest pressures. The curve of VE against the mole fraction x is very asymmetrical at low pressures, but becomes more symmetrical with rising pressure. The effect of pressure on the excess functions GE, HE and T·SE has been calculated. HE and T·SE prove to be much more sensitive to pressure than GE. Conformal solution theory, in the van der Waals one-fluid form, reproduces the experimental results very successfully.

Dimerization and thermodynamic properties of nitric oxide

Abstract Measurements are presented of p-v-T properties of saturated and compressed liquid nitric oxide which complete an earlier report. It can be shown that literature values on the critical properties are in error. The new estimations are T c = 177 K, p c = 5.834 MPa, and v c = 70.62 cm 3 mol −4 , with an uncertainty (due to extrapolation) of 0.5 % in T c and 3 % in p c and v c (the four digits in p c and v c are given because of use in subsequent calculations). The anomalies of the temperature dependencies of orthobaric liquid volume, vapour pressure, and isothermal compressibility are characterized and explained by the varying degree of dimerization. The amount of dimers could be quantitatively estimated by a novel form of the theory of corresponding states for mixtures.

Simple liquid mixtures under pressure and the van der waals - one fluid theory

Abstract pVT measurements performed on a series of simple liquid mixtures at pressures up to 140MPa (Ar + Kr, Ar + CH 4 , Ar + N 2 , Kr + Xe, Kr + CH 4 , CO + CH 4 , N 2 + CH 4 ) allowed the calculation of excess properties over a wide range of temperatures and pressures. The van der Waals - one fluid model of Leland and Rowlinson successfully reproduces the experimental values for all systems studied. The agreement is particularly striking for excess enthalpies and excess entropies, which are the most sensitive functions of pressure and temperature.