Thermodynamic Properties Of Ionic Liquids Research Articles

Thermodynamic Study of Alkylsilane and Alkylsiloxane-Based Ionic Liquids.

The thermodynamic properties of ionic liquids (ILs) bearing alkylsilane and alkylsiloxane chains, as well as their carbon-based analogs, were investigated. Effects such as the replacement of carbon atoms by silicon atoms, the introduction of a siloxane linkage, and the length of the alkylsilane chain were explored. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the thermal and phase behavior (glass transition temperature, melting point, enthalpy and entropy of fusion, and thermal stability). Heat capacity was obtained by high-precision drop calorimetry and differential scanning microcalorimetry. The volatility and cohesive energy of these ILs were investigated via the Knudsen effusion method coupled with a quartz crystal microbalance (KEQCM). Gas phase energetics and structure were also studied to obtain the gas phase heat capacity as well as the energy profile associated with the rotation of the IL side chain. The computational study suggested the existence of an intramolecular interaction in the alkylsiloxane-based IL. The obtained glass transition temperatures seem to follow the trend of chain flexibility. An increase of the alkylsilane chain leads to a seemingly linear increase in molar heat capacity. A regular increment of 30 J·K-1·mol-1 in the molar heat capacity was found for the replacement of carbon by silicon in the IL alkyl chain. The alkylsilane series was revealed to be slightly more volatile than its carbon-based analogs. A further increase in volatility was found for the alkylsiloxane-based IL, which is likely related to the decrease of the cohesive energy due to the existence of an intramolecular interaction between the siloxane linkage and the imidazolium headgroup. The use of Si in the IL structure is a suitable way to significantly reduce the IL's viscosity while preserving its large liquid range (low melting point and high thermal stability) and low volatilities.

Synthesis and characterization of physicochemical properties of two new hydroxyl-functionalized ionic liquids

Two hydroxyl functionalized ionic liquids, 1-(2-hydroxyethyl)-3-methylimidazolium acetate [HEMIM][AC], and 1-(2-hydroxyethyl)-3-methylimidazolium propionate [HEMIM][Pro] ionic liquids were synthesized. The ionic liquids were characterized by 1H NMR and 13C NMR respectively. The density ρ, surface tension γ, and viscosity η of the two ionic liquids were measured in the temperature range (288.15–333.15 K). The contributions of anionic structure to molecular volume Vm, standard molar entropy S0 and the crystal energy UPOT, as well as the variation rules of surface entropy Sa, surface energy Ea and sound velocity W were calculated and discussed. In addition, according to Eyring viscosity equation and thermodynamic equation, the activation Gibbs energy of viscous flow activation ΔG≠ is calculated at different temperatures. And the influence of different anions on the thermodynamic properties of ionic liquids was discussed.

A review of group contribution models to calculate thermodynamic properties of ionic liquids for process systems engineering

Ionic liquids are compounds with interesting physical and chemical properties that can be applied to a wide variety of processes. The knowledge of their thermodynamic properties is essential for the design of products and processes. These properties include heat capacity, density, viscosity, thermal conductivity, melting point, surface tension, electrical conductivity, refractive index, thermal decomposition temperature, normal boiling point, critical properties, freezing point, isobaric expansivity, isothermal compressibility and static dielectric constant. However, the experimental database available of such properties for ionic liquids is limited, thus affecting the process design and modeling. Different thermodynamic models have been developed to estimate these properties and, group contribution models offer several advantages for these applications. This review covers different group contribution models reported and applied to estimate the thermodynamic properties of ionic liquids. The application, performance, and accuracy of these models for predicting the ionic liquids properties were analyzed and discussed. Some approaches combining group contribution models with artificial neural networks to estimate the thermodynamic properties of ionic liquids have been also described and exemplified. This review offers a survey of a variety of group contribution approaches that can be used to predict several thermodynamic properties of ionic liquids for process systems engineering.

Prediction of second order derivative thermodynamic properties of ionic liquids using SAFT-VR Morse equation of state

The variable range statistical associating fluid theory (SAFT-VR) equation of state (EoS) based on the Morse potential was used to describe the second order derivative thermodynamic properties of ionic liquids. The isothermal compressibility coefficient, heat capacities, thermal expansion coefficient, isentropic compressibility coefficient, thermal pressure coefficient, and speed of sound of ionic liquids were predicted up to high pressure and temperature. In this regard, the ionic liquids were considered long chain molecules with two associating sites on cation and anion. The model parameters were obtained by fitting the experimental liquid density data. The average deviation of the calculated liquid density was about 0.09%. The predicted results were compared to the ePC-SAFT EoS to evaluate the capability of the SAFT-VR Morse model. The performance of SAFT-VR Morse EoS was comparable with ePC-SAFT, especially in the heat capacity coefficient and the speed of sound. The average deviation of predicted the isothermal compressibility coefficient, thermal expansion coefficient, isochoric heat capacities, isobaric heat capacities, thermal pressure coefficient, isentropic compressibility coefficient, and speed of sound are 6.46%, 8.32%, 8.18%, 9.55%, 8.10%, 2.67%, and 2.98%, respectively. Obtained results prove that SAFT-VR Morse can be used efficiently to predict second order derivative thermodynamic properties of ionic liquid over a wide range of pressure and temperature.

New Experimental Data on Thermodynamic Properties of the Aqueous Solution of N,N-Diethyl-N-methylammonium Bromide and N,N-Diethyl-N-methylammonium Methanesulfonate

In this work, new experimental data on thermodynamic properties of ionic liquid (IL) aqueous solutions are presented. The (vapor + liquid) phase equilibria, liquid density, and dynamic viscosity of binary mixtures composed of N,N-diethyl-N-methylammonium bromide ([NH,1,2,2][Br]), or N,N-diethyl-N-methylammonium methanesulfonate ([NH,1,2,2][CH3SO3]) and water are presented as functions of temperature and composition. Both ILs were synthesized and specific basic characterization including the NMR spectra and the water content determination was done. The basic thermal properties of the pure IL, including the glass-transition temperature, heat capacity at glass transition, and temperature and enthalpy of (solid + solid) phase transition as well as the temperature and enthalpy of melting were determined using the differential scanning calorimetry (DSC) technique. The isothermal (vapor + liquid) equilibrium (VLE) was measured by the ebulliometric method within a temperature range from T = 338.15 to 368.15 K and pressures up to 85 kPa. Experimental VLE data were successfully correlated using the NRTL equation. The experimental VLE data were tested for thermodynamic consistency using the Van Ness test. The liquid density and the dynamic viscosity were determined as a function of IL’s mole fraction over a wide temperature range. For the correlation of physicochemical properties, empirical equations were applied. From the experimental density data, the excess molar volumes were determined and correlated using the Redlich–Kister-type equation.

Comprehensive analysis and correlation of ionic liquid conductivity data for energy applications

Ionic liquids have emerged as potentially safer and more sustainable electrolytes for energy storage and renewable energy applications, such as Li-ion batteries, Na-ion batteries, supercapacitors and fuel cells. Conductivity is one of the key physical properties influencing the performance of an electrolyte in such applications. In this study, an extensive database for conductivity of ionic liquids was compiled, containing around 3800 data points over the temperature range from 234 K to 484 K, from 134 previously published literature sources. A total of 285 unique ionic liquids consisting of 152 unique cations and 82 unique anions, were included. The data were systematically analyzed to gain a deeper understanding of the relationships between the ionic liquid conductivity and various structural parameters, such as cation type, anion type, hydrocarbon chain length and functional groups. The correlations between conductivity and several other transport and thermodynamic properties of ionic liquids were also investigated and the COSMO-RS method was evaluated as a predictive tool for IL conductivity. Finally, the temperature dependence for each individual ionic liquid was correlated using the Arrhenius equation and the VTF equations. This work will assist in improving the design of ionic liquids as electrolytes in energy storage and renewable energy applications.

From volatility to solubility: Thermodynamics of imidazolium-based ionic liquids containing chloride and bromide anions

Ionic liquids (ILs) are effectively used for tuning the composition and the morphology of nanoparticles or stabilizing agents for nanoparticles for catalytic dehydrogenation. Thermodynamic properties of ionic liquids, e.g. vapor pressures and vaporization enthalpies help optimise these processes. Vapor pressures and vaporization enthalpies of the series of 1-alkyl-3-methylimidazolium ionic liquids with chloride and bromide anions have been measured by using quartz-crystal microbalance (QCM). Possible thermal decomposition pathways of [C2C1Im][Br] during vaporization were analyzed by using high-level quantum-chemical methods. These theoretical results explained and supported the absence of decomposition in QCM experimental conditions. According to the measured vapor pressures the [CnC1Im][Cl] and [CnC1Im][Br] series are very suitable for catalytic applications, taking also into account their sufficient thermal stability at the level of 523–543 K. Solubility parameters of ILs and practically relevant solutes were assessed with help of experimental vaporization enthalpies.

Paving the way to solubility through volatility: Thermodynamics of imidazolium-based ionic liquids of the type [CnC1Im][I

Ionic liquids are effectively used for manufacturing of nanoparticles for thermoelectric generators and in the field of hydrogen storage. Development and optimization of these processes require knowledge of the thermodynamic properties of ionic liquids. Thermochemical study of the series of 1-alkyl-3-methylimidazolium iodides is presented in this work. Vapor pressures and vaporization enthalpies have been measured by using quartz-crystal microbalance. Solution enthalpies were measured by using solution calorimetry. Thermodynamics of aqueous solutions, solubility parameters and miscibility of ILs in eleven organic solvents were derived and discussed. The absence of thermal decomposition of [C4C1Im][I] under vaporization conditions has been demonstrated experimentally and theoretically. It has been shown that vaporization enthalpies are linearly dependent on the chain length of the alkyl substituent and linearly dependent on the surface tension. Aqueous-phase enthalpies of formation of alkyl imidazolium cations have been derived with help of solution calorimetry.

An ionic fragments contribution-COSMO method to predict the surface charge density profiles of ionic liquids

A rapid and reliable method to predict the thermodynamic properties of ionic liquids (ILs) is important for both academic study and industrial application. In this study, an ionic fragment contribution COSMO (IFC-COSMO) method is developed to predict the σ-profiles, VCOSMO and ACOSMO of ILs which are the basic parameters to calculate thermodynamic properties. In the IFC-COSMO method, the increments of σ-profiles, VCOSMO and ACOSMO of fragments are obtained through regressing the σ-profiles, VCOSMO and ACOSMO of cations and anions calculated by quantum chemistry COSMO (QC-COSMO) method. Based on the obtained increments of σ-profiles, VCOSMO and ACOSOM of fragments, the σ-profiles, VCOSMO and ACOSMO of ILs are calculated by linear summation. The results show that the predicted σ-profiles of ILs from the IFC-COSMO method are consistent with those from the QC-COSMO method in overall, and the predicted VCOSMO and ACOSMO agree well with those from the QC-COSMO method showing a low average absolute relative deviation (AARD) of 0.41% and 1.33%, respectively. Afterwards, the equilibrium pressures of binary IL-containing systems are calculated based on the results from IFC-COSMO method. Compared with experimental data, the accuracies of IFC-COSMO and QC-COSMO methods to predict equilibrium pressures are comparable, but the computational cost is much less using IFC-COSMO method due to its independence on the quantum chemistry. Thus, the proposed IFC-COSMO method is an effective method to calculate σ-profiles, VCOSMO and ACOSMO of ILs, then to predict the vapor-liquid phase equilibrium of systems containing ILs.

Conceptual Design of an Energy-Efficient Process for Separating Aromatic Compounds from Naphtha with a High Concentration of Aromatic Compounds Using 4-Methyl-N-butylpyridinium Tetrafluoroborate Ionic Liquid

To obtain aromatic compounds from a crude mixture such as reformate or pyrolysis gasoline, three different processes are simulated with the realistic composition of reformate and product specification. Simulations were performed by Aspen Plus supported with COSMO-RS method to predict the physical and thermodynamic properties of ionic liquid. Furthermore, utility analysis and economic evaluation are presented. Conventionally, aromatic compounds are extracted from a crude mixture either by extraction or by extractive distillation using a solvent such as sulfolane and separated by a series of distillation columns. In this study, the sulfolane-based commercial process is first introduced, and two novel processes that use 4-methyl-N-butylpyridinium tetrafluoroborate ionic liquid as solvent are proposed. The second process shows that energy consumption has successfully decreased, but the high price of ionic liquid offset the cost advantage. The third process is therefore proposed to reduce the amount of ionic l...

Synthesis and characterization of physical, thermal and thermodynamic properties of ionic liquids based on [C12mim] and [N444H] cations for thermal energy storage

This work characterizes the ionic liquids (ILs) [N444H][Cl], [N444H][Tf2N], [N444H][PF6], [C12mim][Cl], [C12mim][Tf2N] and [C12mim][PF6] for use in thermal energy storage. The thermal properties of these liquids have not been reported previously. The liquids were synthesized and characterized by nuclear magnetic resonance (NMR), elemental analysis (EA), and Fourier transform infrared spectroscopy (FTIR). Physical properties including density, speed of sound, and dynamic viscosity were measured at different temperatures. Thermal properties were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the ILs combined with the [Tf2N] anion had good thermal properties for use as heat transfer fluids (HTF), such as wide temperature ranges as liquids and high decomposition temperatures. The thermal storage densities of [C12mim][Tf2N] and [N444H][Tf2N] are 177 and 200MJm−3, respectively.

The study of thermodynamic properties of the ternary (1-ethyl-3-methylimidazolium hydrogen sulfate + lithium chloride + water) system and corresponding binary systems at different temperatures and ambient pressure

Thermodynamic properties of ionic liquid, 1-ethyl-3-methylimidazolium hydrogen sulfate ([Emim][HSO4]) in lithium chloride (LiCl) aqueous solutions have been investigated. Osmotic and activity coefficients of the ternary system ([Emim][HSO4]+LiCl+H2O) and their corresponding binary mixtures at T=298.15K are evaluated using isopiestic method. Using these data, the vapor pressures for these systems are determined. For binary systems, the Pitzer, Pitzer-Archer and modified-Pitzer models are satisfactorily correlated to the osmotic coefficients data. The Scatchard neutral-electrolyte model is fitted to the osmotic coefficients for ternary systems and corresponding mean activity coefficients for the binary and ternary systems are appraised. The densities of the ternary system ([Emim][HSO4]+LiCl+H2O) are measured at T=(293.15–313.15) K using a vibrating U-tube densimeter. Based on experimental density data, the apparent molar volumes, Vφ, are computed. The equation that reported in Redlich-Meyer article was used to correlate the Vφ values and apparent molar volumes at infinite dilution, Vφ0, are also calculated. Our results showed a negative transfer volume of [Emim][HSO4] from water to the aqueous (LiCl) solution which decreases by enhancing the (LiCl) mass fraction and temperature. The solute–solvent interactions and structure making or breaking ability of 1-ethyl-3-methylimidazolium hydrogen sulfate have been discussed in details.

Synthesis and thermodynamic properties of a new task-specific ionic liquid 1-butyl-3-methylimidazolium salicylate

Task-specific ionic liquid 1-butyl-3-methylimidazolium salicylate ([BMI]Sal) was synthesized in two steps. In the temperature range of 298.15–353.15 K, the density and surface tension for pure ionic liquid were determined and the thermodynamic properties of the ionic liquid were discussed in terms of Glasser’s theory. The standard molar entropy and lattice energy for [BMI]Sal have been estimated. In addition, the thermal expansion coefficient, α = 5.53 × 10−4 K−1, calculated by the interstice model is in extreme agreement with α (experimental) = 5.50 × 10−4 K−1.

Excess thermodynamic properties of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate and N-octyl-2-pyrrolidone from T = (298.15 to 323.15) K at atmospheric pressure

Density (ρ), refractive index (nD) and speed of sound (u) values are measured for the binary mixture of 1-butyl-3-methylimidazolium tetrafluoroborate and N-octyl-2-pyrrolidone over the entire range of mole fraction at temperatures from T=(298.15 to 323.15)K under atmospheric pressure. Using the basic experimental data, various acoustic and excess thermodynamic parameters are calculated and are discussed in terms of molecular interactions between the present investigated binary system. The excess values are fitted to Redlich–Kister polynomial equation to estimate the binary coefficients and standard deviation between the experimental and calculated values. Further, the molecular interactions in the binary mixture system are analysed using the experimental FT-IR spectrum recorded at room temperature.

Determination of the solubility parameter of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate by inverse gas chromatography.

Thermodynamic properties of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM] BF4) were determined via inverse gas chromatography (IGC). Two groups of solvents with different chemical natures and polarities were used to obtain information about [BMIM] BF4-solvent interactions. The specific retention volume, molar heat of sorption, weight fraction activity coefficient, Flory-Huggins interaction parameter as well as solubility parameter were also determined in a temperature range of 333 - 373 K. The results showed that the selected solvents n-C10 to n-C12, carbon tetrachloride, cyclohexane and toluene were poor solvents for [BMIM] BF4, while dichloromethane, acetone, chloroform, methyl acetate, ethanol and methanol were favorite solvents for [BMIM] BF4. In addition, the solubility parameter of [ BMIM] BF4 was determined as 23.39 (J/cm3)0.5 by the extrapolation at 298 K. The experiment proved that IGC was a simple and accurate method to obtain the thermodynamic properties of ionic liquids. This study could be used as a reference to the application and research of the ionic liquids.

Study on Thermodynamic Properties of Ionic Liquid 1-Ethyl-3-methylimidazolium Alanine

用中和法合成了氨基酸离子液体1-乙基-3-甲基咪唑丙氨酸([C2mim][Ala]),并利用恒温环境的溶解反应热量计,在(288.15±0.01)K-(308.15±0.01)K温度范围内每隔5K,测定不同质量摩尔浓度离子液体在水中的溶解焓(△sol Hm).根据Archer的方法,通过线性拟合得到了该离子液体的标准摩尔溶解焓(△solHmθ),并计算了其相对表观摩尔溶解焓(ΦL).在298.15 K下,根据Glasser经验方法得到了格子能UPOT=566 kJ· mol-1,并计算了其阴阳离子水化焓值(△H++ △H-)=-620 kJ·mol-1及阴离子水化焓△H-([Ala]-)=-387 kJ· mol-1此外,估算了[C2mim][Ala]水溶液的热容(Cp(sol))和表观摩尔热容(ΦCp).

Surface thermodynamic properties of ionic liquids from new molecular thermodynamic model and ion-contribution equation of state

We aim to develop a new molecular thermodynamic model for predicting the surface thermodynamic properties of pure ionic liquids (ILs) based on the statistical mechanical expression developed by Winterfeld et al. (1978. AIChE. J. 24, 1010). In this respect, contributions to surface tension from the hard-sphere repulsion, Lennard–Jones dispersion force, and electrostatic interactions were considered and assumed to be additive in the development of the model. According to Winterfeld et al. approach, the surface tension of ILs is closely related to their pair potential function, pair radial distribution function and liquid densities. The required densities were predicted from our previous ion-contribution equation of state. The reliability of the proposed model was checked by calculating 464 surface tension data points for 13 different ILs over temperature range within 268.6–393K. The overall average absolute deviation of the correlated surface tensions from the experimental ones was found to be 1.55%. This result demonstrates the good performance of the proposed model and the rationality of molecular parameters, i.e., the soft-sphere diameter, σ dispersive energy, ε and inverse shielding length parameter, Γ. The uncertainty of the predicted surface tension was of the order of ±8.14%. Finally, our method has also been employed to estimate the sound velocities in ILs. The uncertainty of the calculated sound velocities was equal to ±9.25%.

Determination of the thermodynamic parameters of ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate by inverse gas chromatography

Inverse gas chromatography (IGC) was used to characterize the thermodynamic properties of ionic liquid (IL) 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM] BF4) in the temperature range from 343.15 K to 373. 15 K. A series of solvents with different chemical natures were used to determine the [HMIM] BF4-solvent interactions. The thermodynamic parameters including Flory-Huggins interaction parameter, partial molar heats of sorption, mixing and evaporation as well as the activity coefficient at infinite dilution were obtained to judge the interactions between [HMIM]BF4 and the selected solvents. In addition, the solubility parameters of [HMIM] BF4 at different temperatures were determined. The results showed that among the selected solvents, n-C6, n-C7, n-C8, n-C9, diethyl ether, tetrahydrofuran, benzene and cyclohexane were poor solvents for [HMIM] BF4, while toluene, m-xylene, methanol, ethanol, dichloromethane, tetrachloromethane, chloroform, acetone, ethyl acetate and methyl acetate were the favorite ones. The solubility parameter of [HMIM]BF4 at room temperature (298.15 K) was 23.70 (J x cm(-3)(0.5), which was obtained by the linear extrapolation method. The experiment proved that IGC is a simple and accurate method to obtain the thermodynamic properties of ionic liquids. The obtained thermodynamic parameters revealed the strength of the interactions between the selected solvents and the ionic liquid, which could be used as a reference to the further applications of the ionic liquid.

Ecotoxicity of Pyridinium Based Ionic Liquids: A Review

Ionic Liquids (ILs) are an exciting class of compounds with unique properties that make them attractive for industrial applications. Pyridinium-based ILs have been used in many applications, such as organic synthesis, electrochemical applications, biocatalysis, and polymerization. Although intensive information and data regarding to the physical and thermodynamic properties of ILs have been reported and continuously published, only limited data with regards to the toxicity and ecotoxicity of ILs were reported. Toxicity tests are conducted against many aquatic organisms such as: Guppy fish, Gold fish, and Zebra fish, besides many different strains of Microorganisms such as: Staphylococcus aureus, E. coli, and Salmonella typhi, and yet more research regarding the toxicity of ionic liquids is yet to be conducted to increase the toxicity profile for these valuable chemicals.

Exergy analysis of an ionic-liquid absorption refrigeration system utilizing waste-heat from datacenters

Ionic-liquid (IL) was introduced as an absorbent of an absorption refrigeration system designed for high power electronics cooling. IL is a salt in liquid-state, which is nonvolatile, thermally-stable, nonflammable, and environmentally-benign. It provides an alternative to the normally toxic working fluids, such as ammonia, also eliminates crystallization and metal-compatibility issues of the water/LiBr system. The performance of IL absorption refrigeration system was theoretically examined using exergy analysis. Various combinations of refrigerant and imidazolium-based ILs were chosen as working fluid pairs. The thermodynamic properties of ILs were evaluated using the correlations based on group contribution methods. A non-random two-liquid (NRTL) model was built and used to predict the solubility of the mixtures. Both the coefficient of performance (COP) and the exergetic coefficient of performance (ECOP) were evaluated. The effects of operating conditions on ECOP were explored. Also, the exergy destruction of each component was evaluated and discussed as a means to identify the critical component(s) of the system that would require optimization.