Ramesh L. Gardas

Measurements and Correlation of High-Pressure Densities of Imidazolium-Based Ionic Liquids

In the present work, experimental density measurements are reported along with the derived thermodynamic properties, such as the isothermal compressibility (κT), the isobaric expansivity (Rp), and the thermal pressure coefficient (γV) for imidazolium-based ionic liquids (ILs), namely, 1-ethyl-3-methylimidazolium methylsulfate [C2mim][MeSO4], 1-ethyl-3-methylimidazolium ethylsulfate [C2mim][EtSO4], 1,3-diethylimidazolium bis(trifluoromethylsulfonyl)imide [C2eim][Tf2N], and 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C10mim][Tf2N] in the pressure (0.10 < P/MPa < 35.00) and temperature (293.15 < T/K < 393.15) domains. It is shown that experimental densities are in good agreement with the predicted densities obtained by the Gardas and Coutinho method and the correlation using the Tait equation and Sanchez-Lacombe equation of state.

Thermodynamic studies of ionic interactions in aqueous solutions of imidazolium-based ionic liquids [Emim][Br] and [Bmim][Cl].

Experimental measurements of density at different temperatures ranging from 293.15 to 313.15 K, the speed of sound and osmotic coefficients at 298.15 K for aqueous solution of 1-ethyl-3-methylimidazolium bromide ([Emim][Br]), and osmotic coefficients at 298.15 K for aqueous solutions of 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) in the dilute concentration region are taken. The data are used to obtain compressibilities, expansivity, apparent and limiting molar properties, internal pressure, activity, and activity coefficients for [Emim][Br] in aqueous solutions. Experimental activity coefficient data are compared with that obtained from Debye-Hückel and Pitzer models. The activity data are further used to obtain the hydration number and the osmotic second virial coefficients of ionic liquids. Partial molar entropies of [Bmim][Cl] are also obtained using the free-energy and enthalpy data. The distance of the closest approach of ions is estimated using the activity data for ILs in aqueous solutions and is compared with that of X-ray data analysis in the solid phase. The measured data show that the concentration dependence for aqueous solutions of [Emim][Br] can be accounted for in terms of the hydrophobic hydration of ions and that this IL exhibits Coulombic interactions as well as hydrophobic hydration for both the cations and anions. The small hydration numbers for the studied ILs indicate that the low charge density of cations and their hydrophobic nature is responsible for the formation of the water-structure-enforced ion pairs.

Thermophysical properties of ionic liquids

Low melting point salts which are often classified as ionic liquids have received significant attention from research groups and industry for a range of novel applications. Many of these require a thorough knowledge of the thermophysical properties of the pure fluids and their mixtures. Despite this need, the necessary experimental data for many properties is scarce and often inconsistent between the various sources. By using accurate data, predictive physical models can be developed which are highly useful and some would consider essential if ionic liquids are to realize their full potential. This is particularly true if one can use them to design new ionic liquids which maximize key desired attributes. Therefore there is a growing interest in the ability to predict the physical properties and behavior of ionic liquids from simple structural information either by using group contribution methods or directly from computer simulations where recent advances in computational techniques are providing insight into physical processes within these fluids. Given the importance of these properties this review will discuss the recent advances in our understanding, prediction and correlation of selected ionic liquid physical properties.

Alkyltributylphosphonium chloride ionic liquids: synthesis, physicochemical properties and crystal structure.

A series of alkyltributylphosphonium chloride ionic liquids, prepared from tributylphosphine and the respective 1-chloroalkane, C(n)H(2n+1)Cl (where n = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12 or 14), is reported. This work is a continuation of an extended series of tetraalkylphosphonium ionic liquids, where the focus is on the variability of n and its impact on the physical properties, such as melting points/glass transitions, thermal stability, density and viscosity. Experimental density and viscosity data were interpreted using QPSR and group contribution methods and the crystal structure of propyl(tributyl)phosphonium chloride is detailed.

Effect of protic ionic liquid on the volumetric properties and taste behaviour of sucrose

The volumetric properties and taste behaviour of sucrose in aqueous solutions of a protic ionic liquid (3-hydroxypropylammonium acetate) have been studied at temperatures, T=(293.15-318.15)K and at atmospheric pressure. Apparent molar volumes, V2,ϕ, apparent specific volumes, ASV, apparent molar isentropic compressibilities, Ks,2,ϕ, and apparent specific isentropic compressibilities, ASIC, were calculated from measured density, ρ and speed of sound, u data. Partial molar volumes, V2(°), and partial molar isentropic compressibilities, Ks,2(°) at infinite dilution, transfer parameters (ΔtV2(°) and ΔtKs,2(°)), expansion coefficients, [(∂V2(°)/∂T)P and (∂(2)V2(°)/∂T(2))P], interaction coefficients, (YAB and YABB) and hydration numbers, Nw, were also evaluated and discussed in terms of solute-cosolute interactions. Further, the effect of protic ionic liquid on the taste behaviour of sucrose has been discussed from ASV and ASIC parameters, as these parameters, which are sensitive to solvation behaviour of solute, are divided into four basic taste qualities occupying certain ranges.

Speeds of sound and isentropic compressibilities of binary mixtures containing trialkylamines with alkanes and mono-alkylamines at 303.15 and 313.15 K

Abstract Isentropic compressibilities κS, and excess isentropic compressibilities κSE have been determined from measurements of speeds of sound u and densities ρ of 14 binary mixtures of triethylamine (TEA) and tri-n-butylamine (TBA) with n-hexane, n-octane, iso-octane, n-propylamine, n-butylamine, n-hexylamine and n-octylamine. The relative magnitude and sign of κSE have been interpreted in terms of molecular interactions and interstitial accommodation. The values of κSE for TEA + alkane are positive while for TBA + alkane are negative. The values of κSE for TEA + primary amine become progressively less positive and eventually to negative with the increase in chain length of alkylamine. In case of TBA + primary amine, the values of κSE increase from n-propylamine to n-butylamine, and then decrease with chain length of primary amine. The experimental speeds of sound u have been analyzed in terms of collision factor theory, free length theory and Prigogine–Flory–Patterson statistical theory of solutions.

Viscosity of binary mixtures of cycloalkane with cycloalkane, alkane and aromatic hydrocarbon at 303.15 K

Abstract The viscosity ν for eighteen binary mixtures cyclopentane + cyclohexane and + cyclooctane; cyclohexane + cycloheptane, + cyclooctane, + methylcyclohexane, + n-hexane, + n-heptane, + n-octane, + i-octane, + benzene, + toluene, + ethylbenzene, + p-xylene, and + propylbenzene; methylcyclohexane + n-hexane, + i-octane, and + benzene; and cyclooctane + benzene have been reported at 303.15 K over the entire range of composition. The viscosity deviations Δν and excess Gibbs energy of activation ΔG ∗E of viscous flow based on Eyrings theory have been calculated. The effects of molecular sizes and shapes of the component molecules and of interaction energy in the mixture have been discussed. The viscosity data have been correlated with the equations of Grunberg and Nissan, Hind, McLaughlin and Ubbelohde, Tamura and Kurata, Katti and Chaudhri, McAllister, Heric and Brewer, and of Auslaender.

Eco-efficient and green method for the enhanced dissolution of aromatic crude oil sludge using ionic liquids

The upstream petroleum industry faces operational and technical problems due to increased deposition of waxes, aromatics and asphaltene from crude oil sludge in oil storage tanks in the form of tank-bottom sludge (TBS). This results in huge production losses, and threatens environmentally safe operation; therefore, safer solutions are needed. In this work, nine aromatic ionic liquids (ILs) are synthesized and tested for the dissolution of TBS with the aid of five solvents, namely, toluene, heptane, decane, ethyl acetate and hexane. The UV absorbance values of the standard solutions (TBS in solvent) are compared with the sample solutions (TBS in solvent + ILs). It is observed that ILs significantly improve the dissolution of TBS in solvents compared with neat solvent alone. Different weight ratios of TBS : ILs (1 : 1, 1 : 0.5 and 1 : 0.1) are considered in this study. Ionic liquids (ILs) based on an imidazolium cation and various anions, such as [Cl]−, [Br]−, [BF4]−, [H2PO4]−, [HSO4]−, and [PF6]−, are considered in this investigation. It is observed that the dissolution of TBS in heptane in the presence of [HMIM]+[Br]− is efficient to a maximum extent of 66% with other solvents showing similar increased solubility effect with various ILs. In the case of hexane, it should be noted that the efficiency of dissolution of TBS goes on decreasing with increasing concentration of TBS in hexane. A hold-time study is also performed with heptane containing ILs and heptanes without ILs to determine the maximum time required for efficient dissolution of TBS. It is observed that the efficiency is increased beyond 66% in the presence of ILs for the dissolution of TBS in heptane, provided that the mixture of solvent and ILs are in contact with the TBS for a prolonged period of 30 days, or even longer as required. FT-IR and 13C-NMR spectral analyses are also performed so as to understand the efficiency of the ILs in the dissolution of TBS in various solvents, and it was observed that there is a decrease in the intensity of the peaks in the spectra of treated TBS with solvents, which is further enhanced by the addition of ILs.

Elucidation of molecular interactions between a DBU based protic ionic liquid and organic solvents: thermophysical and computational studies

Precise determination of thermodynamic properties of binary mixtures containing ionic liquids (ILs), plays an important role in process design and potential engineering applications of these mixtures. Thermodynamic studies can provide an insight into the nature of intermolecular interactions occurring between the solute and solvent in solutions. In this regard, thermodynamic properties of 1,8-diazabicyclo[5.4.0]undec-7-en-8-ium trifluoroacetate [DBUTFA] in two organic solvents viz. N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) have been evaluated at different temperatures (293.15 to 328.15) K. Apparent molar property data were fitted to a Redlich–Mayer type of equation to compute infinite dilution values and empirical parameters. The experimental studies suggest that the nature of the interactions between DBUTFA and organic solvents are influenced by temperature. DBUTFA interacts more strongly with DMF at low temperature ( 308.15 K). Density functional level of theory (DFT) was employed to investigate intra-ionic and inter-ionic interactions between the ions of PIL and organic solvents. The computational results are in good agreement with experimental results.

Apparent molar properties of aqueous protic ionic liquid solutions at T = (293.15 to 328.15) K

Apparent molar volumes and apparent molar isentropic compressibilities of newly synthesized ammonium-based protic ionic liquid (PIL), namely diethylethanolammonium propionate, at T = (293.15 to 328.15) K and at atmospheric pressure were obtained from experimentally measured density and speed of sound data. Redlich-Mayer type of equation was used to calculate infinite dilution apparent molar volumes, V2∞, infinite dilution apparent molar isentropic compressibilities, Ks,2∞, and corresponding empirical parameters (Sv, Bv, Sk, and Bk). Positive magnitude of limiting volumetric slope Sv versus m1/2 for protic ionic liquid (PIL) + water binary solutions, suggests that PIL-water interactions are weak. Further, the temperature dependence of V2∞ values has also been evaluated.