Activity coefficients at infinite dilution of organic solutes in the ionic liquid,methyl(trioctyl)ammonium thiosalicylate, [N1888][TS] by gas–liquid chromatography at T = (303.15, 313.15, and 323.15) K

In this work, activity coefficients at infinite dilution (${\gamma }_{13}^{\infty }$) have been obtained for 19 polar and non-polar organic solutes in the form of n-alkanes, cycloalkanes, 1-alkenes, 1-alkynes, aromatic compounds, and ketones in the ionic liquid methyl(trioctyl)ammonium thiosalicylate by gas–liquid chromatography at three different temperatures, i.e. T = (303.15, 313.15, and 323.15) K. Two columns with different phase loadings of the ionic liquid in the stationary phase (25% and 30%) were employed to obtain ${\gamma }_{13}^{\infty }$ values at each temperature investigated. Partial molar excess enthalpies at infinite dilution ($\mathrm{\Delta }{H}_1^{\text{E,}\infty }$) were calculated for each of the solutes from the temperature dependency of the ${\gamma }_{13}^{\infty }$ values for the temperature range in this study. Selectivity values at infinite dilution ($S_{\text{ij}}^{\infty }$) were computed from the ${\gamma }_{13}^{\infty }$ values to screen the potential candidacy of the ionic liquid for the separation of n-hexane/benzene mixtures. The results from this study have been compared to those available for several other classes of ionic liquids and commercial solvents employed in solvent-enhanced industrial separation processes.     

Liquid-liquid phase equilibrium of (piperidinium-based ionic liquid + an alcohol) binary systems and modelling with NRHB and PCP-SAFT

The phase diagrams for binary systems of {1-propyl-1-methylpiperidinium bis{(trifluoromethyl)sulfonyl}imide [PMPIP][NTf₂] + an alcohol (butan-1-ol, pentan-1-ol hexan-1-ol, heptan-1-ol, octan-1-ol, decan-1-ol and undecan-1-ol} have been determined at atmospheric pressure using a dynamic method. The influence of an alcohol chain length is discussed for this ionic liquid (IL). A systematic decrease in the solubility is observed with an increase of the alkyl chain length of an alcohol. Liquid + liquid phase equilibrium (LLE) with an upper critical solution temperature was observed. The phase diagrams reported are compared to systems published earlier with the 1-alkyl-1-methylpiperidinium-based ionic liquid. The basic thermal properties of the pure IL, i.e. melting temperature and the enthalpy of fusion, the glass transition temperature and heat capacity at melting temperature have been measured using a differential scanning microcalorimetry technique. The density of [PMPIP][NTf₂] as a function of temperature was measured. The results of the LLE correlation with two models viz. the lattice theory based on non-random hydrogen bonding (NRHB) and the Perturbed-Chain Polar Statistical Associating Fluid Theory (PCP-SAFT) are presented. Both models are capable of describing pure fluid properties of IL (densities and solubility parameters) by using one set of parameters and the LLE in binary systems. This is to our knowledge the first paper presenting the SAFT modelling of binary LLE in ionic liquid systems.     

Vapor–liquid equilibrium in the n-butane + methanol system,measurement and modeling from 323.2 to 443.2 K

New experimental vapor–liquid equilibrium (VLE) data for the n-butane + methanol binary system are reported over a wide temperature range from 323.2 to 443.2 K and pressures up to 5.4 MPa. A static–analytic apparatus, taking advantage of two pneumatic capillary samplers, was used. The phase equilibrium data generated in this work are in relatively good agreement with previous data reported in the literature. Three different thermodynamic models have been used to represent the new experimental data. The first model is the cubic-based Peng–Robinson equation of state (EoS) combined with the Wong–Sandler mixing rules. The two other models are the non-cubic SAFT-VR and PC-SAFT equations of state. Temperature-dependent binary interaction parameters have been adjusted to the new data. The three models accurately represent the new experimental data, but deviations are seen to increase at low temperature. A similar evolution of the binary parameters with respect to temperature is observed for the three models. In particular a discontinuity is observed for the k_ij values at temperatures close to the critical point of butane, indicating the effects of fluctuations on the phase equilibria close to critical points.     

Clathrate hydrates modelled with classical density functional theory coupled with a simple lattice gas and van der Waals-Platteeuw theory

Predicting clathrate hydrate phase equilibria is of interest in the area of natural gas exploitation. This proof of concept study presents the application of a simple lattice gas model and classical density functional theory coupled with van der Waals-Platteeuw theory to predict clathrate hydrate phase equilibria for several different hydrate-forming gas species. The dissociation pressure curve is predicted using adsorption isotherms predicted for the gas species in the crystal hydrate lattice. Comparisons are made between predicted phase equilibria (and other properties) and available experimental data.     

Estimation of pure component properties: Part 3. Estimation of the vapor pressure of non-electrolyte organic compounds via group contributions and group interactions

A group contribution method for the estimation of the normal boiling point of non-electrolyte organic compounds, which was published earlier, has been the basis for development of subsequent physical property methods. In this work, the model was extended to enable the prediction of vapor pressure data with special attention to the low-pressure region. The molecular structure of the compound and a reference point, usually the normal boiling point, are the only required inputs and enables the estimation of vapor pressure at other temperatures by group contribution. The structural group definitions are similar to those proposed earlier for the normal boiling point, with minor modifications having been made to improve the predictions. Structural groups were defined in a standardized form and fragmentation of the molecular structures was performed by an automatic procedure to eliminate any arbitrary assumptions. The new method is based on vapor pressure data for more than 1600 components. The results of the new method are compared to the Antoine correlative equation using parameters stored in the Dortmund Data Bank, as well as, the DIPPR vapor pressure correlations. The group contribution method has proven to be a good predictor, with accuracies comparable to the correlations. Moreover, because the regression of group contributions was performed for a large number of compounds, the results can in several cases be considered more reliable than those of the correlative models that were regressed to individual components only. The range of the method is usually from about the triple or melting point to a reduced temperature of 0.75–0.8.