No abstract

A knowledge of various thermophysical (in particular transport) properties of ionic liquids (ILs) is crucial from the point of view of potential applications of these fluids in chemical and related industries. In this work, over 13 000 data points of temperature- and pressure-dependent viscosity of 1484 ILs were retrieved from more than 450 research papers published in the open literature in the last three decades. The data were critically revised and then used to develop and test a new model allowing in silico predictions of the viscosities of ILs on the basis of the chemical structures of their cations and anions. The model employs a two-layer feed-forward artificial neural network (FFANN) strategy to represent the relationship between the viscosity and the input variables: temperature, pressure, and group contributions (GCs). In total, the resulting GC-FFANN model employs 242 GC-type molecular descriptors that are capable of accurately representing the viscosity behavior of ILs composed of 901 distinct ions. The neural network training, validation, and testing processes, involving 90, 5, and 5% of the whole data pool, respectively, gave mean square errors of 0.0334, 0.0595, and 0.0603 log units, corresponding to squared correlation coefficients of 0.986, 0.973, and 0.972 and overall relative deviations at the level of 11.1, 13.8, and 14.7%, respectively. The results calculated in this work were shown be more accurate than those obtained with the best current GC model for viscosity of ILs described in the literature.

A detailed knowledge of reliable data on physical properties of ionic liquids (ILs) is of great importance, because ILs are still considered as potential replacements for volatile organic solvents in modern and sustainable (“greener”) processes of chemical industry. In particular, liquid density is a very important property that is required in many design problems of chemical engineering and material science. Therefore, development of new methods for estimation of density of ILs is essential. In this work we propose a new method based on generalized empirical correlation and group contributions. It was developed based on a comprehensive database of experimental data containing over 18500 data points for a great variety of 1028 ILs. The collected data covers temperature and pressure ranges of 253–473 K and 0.1–300 MPa, respectively. Molar volume at reference temperature (298.15 K) and pressure (0.1 MPa) was assumed to be additive with respect to defined set of both cationic and anionic functional groups, whereas a Tait-type equation with four adjustable parameters was adopted to describe temperature–pressure dependence of density (P–ρ–T). The model parameters, including contributions to molar volume for 177 functional groups, as well as universal coefficients describing the P–ρ–T surface, were fitted to experimental data for 828 ILs with an average absolute relative deviation (%AARD) of 0.53%. Then, the model was evaluated by a calculation of density for 200 ILs not included in the correlation set. We showed that the proposed GCM allows the accurate prediction of high pressure densities for a variety of ILs. The resulting %AARD of prediction was 0.45% which is the one of the lowest values compared with similar correlations reported in literature. Moreover, we showed that the presented method is able to accurately capture other volumetric properties of pure ILs such as molar volume and derivative properties (thermal expansion coefficient and isothermal compressibility) as well as their temperature and pressure dependencies.

No abstract

We present the results of an extensive study on a novel approach of modeling ionic liquids (ILs) and their mixtures with molecular compounds, incorporating perturbed-chain statistical associating fluid theory (PC-SAFT). PC-SAFT was used to calculate the thermodynamic properties of different homologous series of ILs based on the bis(trifluormethylsulfonyl)imide anion ([NTf2]). First, pure fluid parameters were obtained for each IL by means of fitting the model predictions to experimental liquid densities over a broad range of temperature and pressure. The reliability and physical significance of the parameters as well as the employed molecular scheme were tested by calculation of density, vapor pressure, and other properties of pure ILs (e.g., critical properties, normal boiling point). Additionally, the surface tension of pure ILs was calculated by coupling the PC-SAFT equation of state with density gradient theory (DGT). All correlated/predicted results were compared with literature experimental or simulation data. Afterward, we attempted to model various thermodynamic properties of some binary systems composed of IL and organic solvent or water. The properties under study were the binary vapor-liquid, liquid-liquid, and solid-liquid equilibria and the excess enthalpies of mixing. To calculate cross-interaction energies we used the standard combining rules of Lorentz-Berthelot, Kleiner-Sadowski, and Wolbach-Sandler. It was shown that incorporation of temperature-dependent binary corrections was required to obtain much more accurate results than in the case of conventional predictions. Binary corrections were adjusted to infinite dilution activity coefficients of a particular solute in a given IL determined experimentally or predicted by means of the modified UNIFAC (Dortmund) group contribution method. We concluded that the latter method allows accurate and reliable calculations of bulk-phase properties in a totally predictive manner.

Liquid-liquid equilibria in binary mixtures that contain a room-temperature ionic liquid and an organic solvent-namely, 1,3-dimethylimidazolium methylsulfate, [mmim][CH 3 SO 4 ], or 1-butyl-3methylimidazolium methylsulfate, [bmim][CH 3 SO 4 ] with an aliphatic hydrocarbon (n-pentane, or n-hexane, or n-heptane, or n-octane, or n-decane), or a cyclohydrocarbon (cyclohexane, or cycloheptane), or an aromatic hydrocarbon (benzene, or toluene, or ethylbenzene, or propylbenzene, or o-xylene, or m-xylene, or p-xylene) have been measured at normal pressure by a dynamic method from 270 K to the boiling point of the solvent. Thermophysical basic characterization of pure ionic liquids are presented obtained via differential scanning calorimetry (TG/DSC), temperatures of decomposition and melting, enthalpies of fusion, and enthalpies of glass phase transition. The liquidus curves were predicted by the COSMO-RS method. For [bmim][CH 3 SO 4 ] the COSMO-RS results correspond much better with experiment than those for [mmim][CH 3 SO 4 ]. This can be explained partly by the stronger polarity of [mmim][CH 3 SO 4 ]. The solubilities of [mmim][CH 3 SO 4 ] and [bmim][CH 3 SO 4 ] in alkanes, cycloalkanes and aromatic hydrocarbons decrease with an increase of the molecular weight of the solvent. The differences of the solubilities in o-, m-, and p-xylene are not significant. By increasing the alkyl chain length on the cation, the upper critical solution temperature, UCST decreased in all solvents except in n-alkanes.

Quaternary ammonium salts, which are precursors of ionic liquids, have been prepared from N,N-dimethylethanolamine as a substrate. The paper includes specific basic characterization of synthesized compounds via the following procedures: nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectra, water content, mass spectroscopy (MS) spectra, temperatures of decompositions, basic thermodynamic properties of pure ionic liquids (the melting point, enthalpy of fusion, enthalpy of solid-solid phase transition, glass transition), and the difference in the solute heat capacity between the liquid and solid at the melting temperature determined by differential scanning calorimetry (DSC). The (solid + liquid) phase equilibria of binary mixtures containing (quaternary ammonium salt + water, or + 1-octanol) has been measured by a dynamic method over wide range of temperatures, from 230 K to 560 K. These data were correlated by means of the UNIQUAC ASM and modified nonrandom two-liquid NRTL1 equations utilizing parameters derived from the (solid + liquid) equilibrium. The partition coefficient of ionic liquid in the 1-octanol/water binary system has been calculated from the solubility results. Experimental partition coefficients (log P) were negative at three temperatures.

The solubilities of 1-alkyl-3-methylimidazolium chloride, [C n mim] [Cl], where n 4, 8, 10, and 12, in 1-octanol and water have been measured by a dynamic method in the temperature range from 270 to 370 K. The solubility data was used to calculate the 1-octanol/ water partition coefficients as a function of temperature and alkyl substituent. The melting point, enthalpies of fusion, and enthalpies of solid ± solid phase transitions were determined by differential scanning calorimetry, DSC. The solubility of [C n mim][Cl], where n 10 or 12 in 1-octanol is comparable and higher than that of [C 4 , is not miscible with 1-octanol and water, consequently, the liquid ± liquid equilibrium, LLE was measured in this system. The differences between the solubilities in water for n 4 and 12 are shown only in a 1 and g 1 solid crystalline phases. Additionally, the immiscibility region was observed for the higher concentration of [C 10 mim][Cl] in water. The intermolecular solute ± solvent interaction of 1-butyl-3-methylimidazolium chloride with water is higher than for other 1-alkyl-3-methylimidazolium chlorides.The data was correlated by means of the UNIQUAC ASM and two modified NRTL equations utilizing parameters derived from the solid ± liquid equilibrium, SLE. The root-mean-square deviations of the solubility temperatures for all calculated data are from 1.8 to 7 K and depend on the particular equation used. In the calculations, the existence of two solid ± solid first-order phase transitions in [C 12 mim][Cl] has also been taken into consideration. Experimental partition coefficients (log P) are negative at three temperatures; this is evidence for the possible use of these ionic liquids as green solvents.