Density, viscosity and electrical conductivity of protic alkanolammonium ionic liquids

Ionic liquids are molten salts with melting temperatures below the boiling point of water, and their qualification for applications in potential industrial processes does depend on their fundamental physical properties such as density, viscosity and electrical conductivity. This study aims to investigate the structure-property relationship of 15 ILs that are primarily composed of alkanolammonium cations and organic acid anions. The influence of both the nature and number of alkanol substituents on the cation and the nature of the anion on the densities, viscosities and electrical conductivities at ambient and elevated temperatures are discussed. Walden rule plots are used to estimate the ionic nature of these ionic liquids, and comparison with other studies reveals that most of the investigated ionic liquids show Walden rule values similar to many non-protic ionic liquids containing imidazolium, pyrrolidinium, tetraalkylammonium, or tetraalkylphosphonium cations. Comparison of literature data reveals major disagreements in the reported properties for the investigated ionic liquids. A detailed analysis of the reported experimental procedures suggests that inappropriate drying methods can account for some of the discrepancies. Furthermore, an example for the improved presentation of experimental data in scientific literature is presented.     

Evaluation of thermal analysis equipment for the determination of vapor pressure and heat of vaporization

A rapid, relatively simple method for determining vapor pressure and heat of vaporization on small amounts of organic compounds is described. A DuPont 900 differential thermal analyzer (DTA), a Perkin—Elmer Model DSC-1B differential scanning calorimeter (DSC), and a Thomas—Hoover (TH) melting point apparatus were evaluated in this work. Vapor pressure data for a wide variety of organic liquids were obtained by measuring the boiling points of the liquids at pressures ranging from 20 to 735 torr. A computer was used to rapidly plot the experimental data. The average deviations of boiling points from the literature values were 2.3°C for the DTA 1.2°C for the DSC, and 1.5°C for the TH. The vapor pressure data were used to solve the Haggenmacher equation for heat of vaporization (ΔH_v). The deviations of the experimental values for ΔH_v. from the literature values were 5.5%, 8.3%. and 3.3% for the DTA, DSC, and TH methods, respectively.     

A simple and generalized model for predicting the density of ionic liquids

A simple and accurate model to predict the density of ionic liquids is presented. The proposed model is based on a generalized correlation that has been conveniently modified and experimental literature data have been used to fit the five model parameters, to finally propose an equation that allows predicting densities of any ionic liquid. The model uses the critical temperature, the critical volume, the normal boiling temperature and the molecular mass to estimate the density at temperatures commonly used in ionic liquid applications (270–360 K). A set of 602 density data for 146 ionic liquids has been used in the study. The results were compared with predictions of ten generalized corresponding states principle correlations available in the literature. These generalized correlations have not been applied to ionic liquids before so the appropriateness and accuracy of these models to ionic liquid density estimation are unknown until now. Results show that the new simple correlation gives low deviations and can be used with confidence in thermodynamic and engineering calculations.     

Nitrous oxide: Saturation properties and the phase diagram

The experimental values of the coordinates of the triple point and of the critical point of nitrous oxide registered in the literature were assessed and those judged as most reliable have been selected. Empirical equations have been found for the vapour pressure, sublimation and fusion curves. The virial coefficients and saturation properties as functions of temperature along the equilibrium curves are described by reduced equations. They were used in arriving at the molar enthalpies at the triple point and the normal boiling temperature. Equations for the sublimation and fusion curves resulting from the exactly integrated Clapeyron equation compare favourably with the results from the empirical treatment and the 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.     

Analysis of thermoelastic properties and equation of state for cyclopentane,tetramethylsilane and 2,3-dimethylbutane

The thermoelastic properties and equation of state for liquids such as cyclopentane, tetramethylsilane and 2,3-dimethylbutane at high pressures and high temperatures have been analysed. The pressure dependences of thermal expansivity and isothermal compressibility have been determined for these liquids under pressure up to 100?MPa along different isotherms at selected temperatures in the range 208.0–298.15?K. We have formulated the pseudospinodal model for different liquids, along different isotherms for evaluating both thermal expansivity and isothermal compressibility with the change in pressure. It is found that the spinodal pressure is a characteristic property of the liquid depending only on temperature. The results obtained in this study are in good agreement with the experimental data reported in the literature. The plots between thermal expansivity versus pressure along different isotherms intersect each other for tetramethylsilane and 2,3-dimethylbutane. However, in the case of cyclopentane the plots do not intersect each other.     

Thermophysical properties of (diphenyl ether + biphenyl) mixtures for their use as heat transfer fluids

Experimental measurements of density, viscosity and thermal conductivity are reported for pure diphenyl ether and three different binary mixtures of diphenyl ether and biphenyl including the eutectic point. Density has been measured for the liquid phase at temperatures ranging from (298.15 to 363.15) K and for pressures up to 45 MPa using a high-pressure vibrating tube densimeter. A Tammann–Tait correlation of the experimental densities has been proposed for each composition. From these correlations, isothermal compressibility, isobaric thermal expansivity and internal pressure have been determined. Moreover, viscosity and thermal conductivity were experimentally determined at atmospheric pressure for several temperatures by using a rolling ball viscometer and a device based in the hot-wire technique, respectively. All the experimental devices used to determine the thermophysical properties were checked finding good agreements with previous literature data. The experimental viscosity values were correlated using the Vogel–Fulcher–Tammann, Avramov–Milchev and MYEGA equation.     

Dependence of Surface Tension of Near-boiling Non-associated Liquids on Their Molar Volume and Some Critical Constants

Abstract

The equation proposed for near-boiling non-associated liquids describes a new functional dependence of their surface tension on such physico-chemical characteristics as: critical volume, critical temperature and molar volume at the temperatures which are near their normal boiling points. It is shown that, in the case of some low-boiling liquids, possessing small molecules, this equation can be used for the adequate calculation of surface tension at different temperatures in the liquid phase.     

On the critical temperature, normal boiling point, and vapor pressure of ionic liquids

One-stage, reduced-pressure distillations at moderate temperature of 1-decyl- and 1-dodecyl-3-methylimidazolium bistriflilamide ([Ntf(2)](-)) ionic liquids (ILs) have been performed. These liquid-vapor equilibria can be understood in light of predictions for normal boiling points of ILs. The predictions are based on experimental surface tension and density data, which are used to estimate the critical points of several ILs and their corresponding normal boiling temperatures. In contrast to the situation found for relatively unstable ILs at high-temperature such as those containing [BF(4)](-) or [PF(6)](-) anions, [Ntf(2)](-)-based ILs constitute a promising class in which reliable, accurate vapor pressure measurements can in principle be performed. This property is paramount for assisting in the development and testing of accurate molecular models.     

Physicochemical properties determined by ΔpKa for protic ionic liquids based on an organic super-strong base with various Brønsted acids

Neutralization of an organic super-strong base, 1,8-diazabicyclo-[5,4,0]-undec-7-ene (DBU), with different Br?nsted acids affords a novel series of protic ionic liquids (PILs) with wide variations in the ΔpK(a) of the constituent amine and acids. The physicochemical properties of these PILs, such as thermal properties, density, conductivity, viscosity, self-diffusion coefficient, vibrational stretching frequency, and (1)H-chemical shifts of the N-H bond, have been studied in detail. The generated PILs have melting temperatures below 100 °C, and six are liquids at ambient temperatures. Thermogravimetric analyses (TGA) conducted under isothermal and programmed heating conditions have shown that PILs with ΔpK(a)≥ 15 exhibit good thermal stability similar to aprotic ionic liquids. For instance, PILs with ΔpK(a) > 20 show remarkably high short-term thermal stability up to ca. 450 °C under a nitrogen atmosphere. The viscosity, ionic conductivity, and molar conductivity of the PILs fit well with the Vogel-Fulcher-Tamman equation for their dependencies on temperature. The relative cationic and anionic self-diffusion coefficients of the PILs estimated by the pulsed-field gradient spin-echo (PGSE) NMR method appear to be dependent on the structure and strength of the Br?nsted acids. Evaluation of the ionicity based on both the Walden plot and PGSE-NMR revealed that it increases until ΔpK(a) becomes 15 for the PILs.     

Again the Riedel equation

Several literature relations to calculate the vapour pressures of pure compounds are re-examined to evaluate their reliability in predicting the experimental data in a very low pressure range, chosen between the triple point and 1 mmHg. Following a previous work of the author, the performances of the Riedel equation are greatly improved by allowing a temperature dependence of the Riedel parameter 0.0838, which is assumed constant in the unmodified Riedel equation. The resulting relations, which vary for each class of compounds, embody only pure component parameters which can be evaluated by knowing only the normal boiling temperature and the critical constants. With these modifications, the Riedel equation is significantly better than the Miller, Lee–Kesler and Ambrose–Walton equations. This superiority is particularly evident in the case of strongly associated compounds, like alcohols. The strong dependence of the calculated pressures at very low temperatures on the critical temperature value is also stressed.

The proposed method is verified on the basis of nearly 90 compounds, by using as “true” experimental data those reported in three sources: the DIPPR Data Compilation of Pure Compounds Properties, Project 801, the NIST program and a literature paper.     

Estimation of the thermal conductivity λ(T,P) of ionic liquids using a neural network optimized with genetic algorithms

In this study, an artificial neural network was optimized using a genetic algorithm in order to estimate the thermal conductivity of ionic liquids at different temperatures and pressures. Experimental thermal conductivity data of 41 ionic liquids (400 experimental data points) in the range from 0.10 to 0.22 W m⁻¹ K⁻¹ were used to obtain the proposed method for the temperature range of 273–390 K and the pressure range of 100–20,000 kPa. In addition, the molecular mass M and structure of molecules, represented by the number of well-defined groups forming the molecule, were provided as input parameters in order to characterize the different molecules of ionic liquids. A heterogeneous set of ionic liquids includes cations such as imidazolium, ammonium, phosphonium, pyrrolidinium, and pyridinium. It also includes anions such as halides, sulfonates, tosylates, imides, borates, phosphates, acetates, and amino acids. The whole dataset was divided into a training set with 300 experimental data points and a prediction set with 100 experimental data points. Several architectures were studied, and the optimum weights for the network were determined. The results showed that the proposed method to estimate the thermal conductivity of ionic liquids at different temperatures and pressures presented a good accuracy with lower deviations such as AARD less than 0.91% and R² of 0.9969 for the training set, and AARD less than 0.84% with R² of 0.9963 for the prediction set.     

A new three-parameter viscosity-temperature equation for saturated liquids from the triple point to the critical point

A new simple viscosity-temperature equation with only three adjustable parameters is proposed that is valid over the entire saturated liquid curve for a chemically diverse set of compounds. This equation can incorporate the correct near-critical behavior and satisfies the need for a reliable equation for fitting and predicting the viscosity of saturated liquids. It reproduces data within the experimental uncertainty over the entire saturated liquid region. Compared with the previous viscosity-temperature equations, the new equation not only more accurately correlates experimental data but also more effectively extrapolates values from the usual range in which data are available both to the critical point and to the triple point.     

Ionic liquids by proton transfer: vapor pressure, conductivity, and the relevance of DeltapKa from aqueous solutions

We describe the behavior of the conductivity, viscosity, and vapor pressure of various binary liquid systems in which proton transfer occurs between neat Br?nsted acids and bases to form salts with melting points below ambient. Such liquids form an important subgroup of the ionic liquid (IL) class of reaction media and electrolytes on which so much attention is currently being focused. Such "protic ionic liquids" exhibit a wide range of thermal stabilities. We find a simple relation between the limit set by boiling, when the total vapor pressure reaches one atm, and the difference in pK(a) value for the acid and base determined in dilute aqueous solutions. For DeltapK(a) values above 10, the boiling point elevation becomes so high (>300 degrees C) that preemptive decomposition prevents its measurement. The completeness of proton transfer in such cases is suggested by the molten salt-like values of the Walden product, which is used to distinguish good from poor ionic liquids. For the good ionic liquids, the hydrogen bonding of acid molecules to the proton-transfer anion is strong enough that boiling points, but not melting points, may maximize at the hydrogen-bonded dianion composition. High boiling liquids of this type constitute an interesting class of high-temperature protonic acid that may have high-temperature fuel cell applications.     

Influence of Temperature on Liquid–Liquid Equilibrium of Methanol + Toluene + Hexane Ternary Systems at Atmospheric Pressure

Phase equilibria of methanol?+?toluene?+?hexane ternary systems at (278.15, 283.15, 288.15 and 293.15) K at atmospheric pressure were investigated. The influence of temperature on the liquid–liquid equilibrium is discussed. All chemicals were quantified using gas chromatograph with a thermal conductivity detector coupled to a ChemStation and nitrogen as gas carrier, their mass fractions were higher than 0.999. From literature are found two articles from the same system at different temperatures studied here. Experimental data are compared with literature values. Values calculated using the NRTL and UNIQUAC equations are compared with the experimental data and it is found that the UNIQUAC equation fitted the experimental data better than the NRTL model for this ternary system.     

Electrolytic conductivity and molar heat capacity of two aqueous solutions of ionic liquids at room-temperature: Measurements and correlations

As part of our systematic study on physicochemical characterization of ionic liquids, in this work, we report new measurements of electrolytic conductivity and molar heat capacity for aqueous solutions of two 1-ethyl-3-methylimidazolium-based ionic liquids, namely: 1-ethyl-3-methylimidazolium dicyanamide and 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate, at normal atmospheric condition and for temperatures up to 353.2 K. The electrolytic conductivity and molar heat capacity were measured by a commercial conductivity meter and a differential scanning calorimeter (DSC), respectively. The estimated experimental uncertainties for the electrolytic conductivity and molar heat capacity measurements were ±1% and ±2%, respectively. The property data are reported as functions of temperature and composition. A modified empirical equation from another researcher [1] was used to correlate the temperature and composition dependence of the our electrolytic conductivity results. An excess molar heat capacity expression derived using a Redlich–Kister type equation was used to represent the temperature and composition dependence of the measured molar heat capacity and calculated excess molar heat capacity of the solvent systems considered. The correlations applied represent the our measurements satisfactorily as shown by an acceptable overall average deviation of 6.4% and 0.1%, respectively, for electrolytic conductivity and molar heat capacity.     

反相液相色谱中同系物保留值与流动相组成的交点规律

本文在作者提出的反相液相色谱中同系物保留值与常沸点的交点规律基础上，推导出系物保留值与流动相组成的交点规律，用大量实验数据作了检验。并用新交点方程式，由化合物在一个流动相组成下的保留值，预测该化合物在任一流动相组成下的保留值，对１４组同系物在５种色谱柱上５类流动相下的验算结果表明，７２１个数据点的绝对平均误差为２．８％。     

Quantitative Structure-Property Relationship: XIII. Properties of Aliphatic Alcohols

A simple quantitative structure-property relationship was used to calculate a set of properties of aliphatic alcohols including the boiling point; enthalpy of vaporization; heat capacity of liquids at constant pressure; entropy, enthalpy, and free energy of formation; free energy of transfer from the gas phase to water; distribution factor in the octanol-water system; dielectric constant; surface tension; viscosity; thermal conductivity; diamagnetic susceptibility; ionization potential; self-association index; distribution factor between the gas and hexadecane; distribution factor between water and dodecyl sulfate mixelles; solubility of HCl in alcohols; and solvatochromic parameter. The rate constants, activation entropies, and activation energies of the Menshutkin reaction in alcohols were also calculated. The calculated values are in good agreement with the experimental data. The suggested relationship well reproduces the proton affinites of a series of alcohols calculated by rigorous methods.