Densities Of Pure Ionic Liquids Research Articles

Density Prediction of Ionic Liquids at Different Temperatures Using the Average Free Volume Model.

In this work, based on the average free volume model, the correlation between the molar volume and the van der Waals volume Vw for the ionic liquids (ILs) was derived. With this model, the density of pure ILs and binary and ternary mixtures of ILs over a wide range of temperature (278–473.15 K) can be calculated with good accuracy only with the information of the chemical components. A total number of 1859 data points of 41 pure ILs and IL mixtures based on imidazolium, pyridinium, pyrrolidinium, phosphonium, and ammonium cations were used to verify the model. For pure ILs and IL mixtures, the average absolute relative deviations (ARDs) are 1.04 and 1.19%, respectively. The overall discrepancies are less than 4%.

Density modelling of ionic liquids using the electrolyte Soave–Redlich–Kwong equation of state

A considerable amount of literature has recently been published on the study of ionic liquids (ILs). Due to their diversity and to the possibility of being designed to fit a specific application, predictive tools are required to understand their properties and their behaviour when mixed with other substances. One of these tools is thermodynamic modelling with equations of state (EoS). In this work, the Soave–Redlich–Kwong equation of state, coupled to the Debye–Hückel electrolyte model, was applied to correlate the densities of pure ILs. It was assumed that the ILs were totally dissociated, forming a binary mixture of cations and anions. In the modelling, the required EoS parameters were assessed through group contribution methods. One scale parameter was introduced to buffer the uncertainty of the calculations, and it was tuned to fit the model to the ILs’ measured densities. Three strategies were adopted to describe the densities in a wide range of temperatures and pressures: (i) adjusting this single IL parameter in order to fit the model to the reported densities at low pressure; (ii) determining it from one measured datum and (iii) from the obtained parameters in the second approach, generating an empirical function that correlates them with their molar masses. At 0.1MPa (458 data points), the overall absolute average deviations from the experimental data were 0.9%, 1.3% and 4.0% for each of these strategies, respectively. High-pressure densities were also predicted (3270 points), with computed deviations from the measurements of 1.4%, 1.4% and 3.4%. The proposed method can be used for IL density predictions, as a function of temperature and pressure, when no or only one measured datum is available.

Prediction of densities of pure ionic liquids using Esmaeilzadeh-Roshanfekr equation of state and critical properties from group contribution method

In this paper, the group contribution Esmaeilzadeh-Roshanfekr (GC-ER) was used to obtain the group increments for normal boiling point, critical temperature, and critical pressure on the basis of 1775 experimental density data for 294 pure ionic liquids forming 35 groups (28 non-ring groups and 7 group rings) at temperature in the range of 273.15 K–473.15 K and ambient pressure. The average absolute relative deviation (AARD) of the proposed model is 11.49%. For validating the model, density of 53 ionic liquids were predicted and compared with 520 experimental literature density data at different temperatures and ambient pressure that average absolute relative deviation is 9.33%. Also the accuracy of model was compared with the group contribution-Patel Tejja (GC-PT), group contribution-Peng Robbinson (GC-PR), and the group contribution-Van der Waals (GC-VW) model. The results showd that the error of the model is lower than that of the other equations that assess in this work.

Modeling the density of ionic liquids with ePC-SAFT

ePC-SAFT was used to model the densities of ionic liquids (ILs) up to high pressures and temperatures. The ILs under consideration contained one of the IL-cations [Cnmim]+, [Cnpy]+, [Cnmpy]+, [Cnmpyr]+ or [THTDP]+, and one of the IL-anions [Tf2N]−, [PF6]−, [BF4]−, [tfo]−, [DCA]−, [SCN]−, [C1SO4]−, [C2SO4]−, [eFAP]−, Cl−, [Ac]− or Br−, respectively. Within the ePC-SAFT framework, IL-ion specific parameters were applied that are valid independent of the IL they are part of. Each IL-ion was modeled as a non-spherical species exerting repulsive, dispersive and Coulomb forces. The ePC-SAFT parameters for [Cnmim]+ (n = 2, 4, 6 and 8), [Tf2N]−, [PF6]−, and [BF4]- were taken from our previous work (Fluid Phase Equilibria 2012 (335) 64–73). Based on these parameters, all parameters of the other IL-ions were fitted to experimental density of pure ILs up to high pressures in a broad temperature range. Being provided with ion-specific and linearly molecular-weight-dependent parameters, ePC-SAFT allows reliably representing/predicting pure-IL and mixed-IL density up to high pressures.

Densities of Pure Ionic Liquids and Mixtures: Modeling and Data Analysis

Our two-parameter corresponding states model for liquid densities and compressibilities has been extended to more pure ionic liquids and to their mixtures with one or two solvents. A total of 19 new group contributions (5 new cations and 14 new anions) have been obtained for predicting pressure effects over wide ranges of temperature and pressure. Comparisons of the technique with contemporary treatments based on equations of state show that it compares favorably with all other approaches.

An artificial neural network to calculate pure ionic liquid densities without the need for any experimental data

In this study, a feed-forward artificial neural network, with three layers and seventeen neurons, was constructed to estimate the densities of a wide range of ionic liquid families including those based on the imidazolium, ammonium, pyridinium, pyrrolidinium, and isoquinolinium cations, together with various anions, as well as varying lengths of alkyl side chain lengths. The model is a function of the molecular weight and structure of the ionic liquid, and the system condition of temperature and pressure, which covers a temperature range of (273.15 to 393.17)K and a pressure range of (0.1 to 100)MPa. Therefore, no additional experimental data on the ionic liquid is required as input parameter(s), which makes this technique quite versatile. It was observed that the estimated values of densities of pure ionic liquids have very good agreement with the experimental data. The training correlating coefficient (R), the training performance (MSE), and the average absolute error on the training dataset were 0.99997, 6.04×10−6, and 0.019%, respectively. The average absolute error value on the test dataset is 0.014%.

P–V–T properties of binary mixtures of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with anisole or acetophenone at elevated pressures

The isothermal densities of pure ionic liquids, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C4mim][NTf2], and its mixtures with anisole or acetophenone were measured by using a vibrating tube densimeter over temperatures ranging from (298.15 to 348.15)K and pressures from (0.1 to 50)MPa. The Tait equation was used to correlate the density data and accurately represents densities varying with pressure at given temperature and composition. The excess volumes were calculated from the experimental data and found that those are all negative, except for (acetophenone+[C4mim][NTf2]) at 298.15K with containing acetophenone of 0.1 in mole fraction. The modified Redlich–Kister was applied to correlate the excess volumes. The Flory–Orwoll–Vrij (FOV) and the Schotte equations of state were also employed to correlate the density data over entire experimental conditions.

Critical properties and acentric factors of ionic liquids

Since most ionic liquids (ILs) decompose before reaching their critical state, the experimental measurement of their critical properties are not possible. In this study, the critical temperatures, critical pressures and acentric factors of ten commonly investigated ILs were determined by making an optimum fit of the calculated vapor-liquid equilibrium data of binary mixtures of CO2+IL to the experimental values found in literature. For this purpose, the Peng-Robinson equation of state (PR EoS) and the differential evolution optimization method were used. The ILs considered were 1-ethyl-3-methylimidazolium hexafluorophosphate ([emim][PF6]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([emim][Tf2N]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([bmim][Tf2N]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim][BF4]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]), 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([hmim][Tf2N]), 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF4]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF6]). To evaluate the ability of the determined parameters in predicting the phase behavior of systems other than the systems that were used for parameter optimization, both sets of parameters obtained in this work and that of Valderrama et al. were used to predict bubble-point pressures of CHF3+[bmim][PF6] (by using the PR EoS and the Soave-Redlich-Kwong equation of state. The bubble-point pressures of CO2+IL systems optimized in this study by the PR EoS were also determined using the Soave-Redlich-Kwong equation of state (SRK EoS). In addition, liquid densities of pure ILs were predicted using a generalized correlation proposed by Valderrama and Abu-Shark. In all cases, the various predicted properties of these ten ILs, were in better agreement with the experimental data, using the critical properties and acentric factor obtained in this study, compared to the values suggested by Valderrama et al.

Volumetric properties of ionic liquids from cubic equation of state: Application to pure and mixture

In this work, we developed a cubic equation of state (CEOS) for modeling the volumetric properties of various ionic liquids (ILs). Two temperature-dependent parameters presented in the CEOS, have been determined from two sets of corresponding states correlations which are based on the critical point data or the surface tension of ILs. The predicted densities of pure ILs were compared with the experimental data over a broad pressure range from 1 to 100MPa. The total average absolute deviations (AADs) of the calculated densities of 948 data points from the experimental data are 1.82% using the critical property and 0.96% using the surface tension and liquid density as scaling parameters. Furthermore, the proposed CEOS was successfully extended to mixtures including IL+IL and IL+solvent systems. 1282 literature data points for mixtures were taken to check the reliability of the mixture version of the proposed CEOS. The AAD of the calculated densities of the mixtures using the surface tension and liquid density as scaling parameter is 0.37%. Furthermore, the excess molar volumes (VE) of the studied binary mixtures have been successfully computed by the use of the proposed CEOS.

Volumetric properties of the ionic liquids: [C6mim][MeSO4], [C6mim][EtSO4], [C4mim][EtSO4] and their mixtures with methanol or ethanol

Densities of pure ionic liquids, 1-hexyl-3-methylimidazolium methylsulfate [C6mim][MeSO4], 1-hexyl-3-methylimidazolium ethylsulfate, [C6mim][EtSO4], 1-butyl-3-methylimidazolium ethylsulfate [C4mim][EtSO4] and their mixtures with either methanol or ethanol, were measured at temperatures T/K=(283.15, 298.15, 313.15, 328.15) at ambient pressure. The excess volumes VE were correlated by the van Laar equation with the temperature-dependent parameters. Isobaric expansivity and excess isobaric expansivity were described as functions of temperature and composition. The negative deviations from ideal mixing were observed for excess volume VE and the excess isobaric expansivity αE.

Group contribution lattice fluid equation of state (GCLF EOS) for ionic liquids

This work focuses on the extension of group parameters and application of the group-contribution lattice-fluid equation of state (GCLF EOS) for the systems with ionic liquids (ILs). The new group parameters ekk and Rkk for ILs in GCLF EOS were obtained by means of correlating the liquid density of pure ILs at different temperatures, while the group binary interaction parameters αmn were obtained by means of correlating the activity coefficients of solutes at infinite dilution in ILs at different temperatures, which were exhaustively collected from references. New IL groups were added into the current parameter matrix. It was verified that GCLF EOS for ILs can be used for predicting liquid densities of pure ILs or the mixture of IL and solute, vapor–liquid equilibria (VLE) and liquid–liquid equilibria (LLE) at finite concentration, as well as identifying the structure–property relation in separation science. This is the first work for us to extend the predictive GCLF EOS to the systems with ILs.

A New Group Contribution Method For Prediction of Density of Pure Ionic Liquids over a Wide Range of Temperature and Pressure

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, w...

Modeling the volumetric properties of mixtures involving ionic liquids using perturbed hard-sphere equation of state

This work addresses a detailed procedure of the application of previously developed equation of state (EOS) to estimate liquid densities of pure ionic liquids (ILs) containing tetrafluoroborate and hexafluorophosphate anions as a function of temperature and pressure. Besides, the present EOS is successfully extended to binary mixtures IL + water, IL + DMSO, IL + ethanol, IL + methanol, IL + 1-propanol, and IL + tetrahydrofuran (THF) to compute their mixture density and excess volumes. In this study, our focus is on improving the previous EOS through a reparametrization procedure. Moreover, we have demonstrated the density behavior of studied ILs in terms of alkyl chain length of imidazolium cation and the anion size via proposed model. The accuracies of our calculations are of the order of ± 3%. The average absolute deviation (AAD) of the calculated densities of pure ILs for 962 examined data points was found to be 1.55%. Finally, the AAD for the mixture densities for 665 examined data points was found to be 0.58%.

Surface Tension and Density of Pure Ionic Liquids and Some Binary Mixtures with 1-Propanol and 1-Butanol

The pendant drop method has been used for measuring the surface tension of the pure ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide, methyltrioctylammonium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium ethylsulfate, and 1-butyl-3-methylimidazolium octylsulfate in the range of (278 to 333) K. In addition, densities and thermal expansion coefficients of these ionic liquids are presented. The values of surface tension lie between (25 and 48) mN·m−1 and decrease with temperature. Surface tension σ of the mixtures of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide + 1-propanol and + 1-butanol have also been determined as a function of the mole fraction at 298 K. Since the pendant drop method requires precise density measurements of the mixtures, densities were also measured.