Excess molar volumes and excess isentropic compressibilities of ternary mixtures containing ionic liquids and cyclic alkanone

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Highlights

  • The VijkE and (κSE)ijk data of ternary mixtures have been measured over entire mole fractions.

  • The VijkE and (κSE)ijk values have been fitted to Redlich-Kister equation.

  • The observed data have been analyzed in terms of Graph and PFP theory.

  • The VijkE and (κSE)ijk data predicted by Graph theory compare well with experimental values.

Abstract

This paper reports densities, ρijk and speeds of sound, uijk data of ternary {1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i) + 1-butyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium tetrafluoroborate (j) + cyclopentanone or cyclohexanone (k)} mixtures at temperatures 293.15 K to 308.15 K using a digital densimeter and speed of sound analyser. The observed ρijk and uijk data have been employed to determine excess molar volumes, VijkE and excess isentropic compressiblities, (κSE)ijk respectively of the studied mixtures. The topology of the constituent molecules (Graph theory) of the binary ionic liquid mixtures has recently been utilized (Gupta et al., 2016) to predict their VE, κSE, HE and CpE data. In the present studies, the topology of the components of the ternary mixtures (comprise of two ionic liquids and one organic solvent) has been employed (Graph theory) to obtain expressions for VijkE and (κSE)ijk data that describe well the measured VijkE and (κSE)ijk values. The observed VijkE and (κSE)ijk values have also been tested in terms of Prigogine-Flory-Patterson (PFP) theory. It has been observed that VijkE and (κSE)ijk values predicted by Graph theory are comparable with the experimental values.

Introduction

In the era of rapidly changing global environment, more and more research attempts have been made to replace fossil fuels (used in devices) for the control of greenhouse gas emissions. Ionic liquids (ILs), a new novel type of green solvents have received widespread attention as an eco-friendly reaction medium for various processes involved in industries [1], [2], [3], [4]. These liquids are composed of an inorganic anion; a bulky organic cation and possess unique properties such as negligible vapor pressure, wide liquid range, non-flammability, excellent solubility, non-volatility, recyclable, reusability, high thermal and electrochemical stability and good selectivity. Due to the unusual and specific properties, ILs can be considered as safer and more sustainable alternative to volatile organic compounds (VOCs) as solvents in various reactions, catalytic activities, extraction systems, adsorption and separation processes [5], [6], [7], [8], [9]. Among the well-known families of ILs, imidazolium based ILs have recently attracted most attention in experimental investigations such as media for bio-electrochemistry, photovoltaic, metal deposition, exploration for absorption/solubility of CO2 and electrolytes in dye sensitized solar cells (DSSCs) to improve the conversion efficiency etc. [10], [11], [12], [13]. 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium tetrafluoroborate are being used in electrochemistry, catalysis, extraction processes, batteries and capacitors [14], [15], [16], [17]. However, pure ILs are highly viscous, and having relatively high cost which impedes their application [18]. Such disadvantages of ILs can be overcome by mixing with some organic solvents [19], [20]. The physico-chemical and thermodynamic properties of IL mixtures such as densities, viscosities, excess molar enthalpies, excess molar volumes, excess heat capacities etc. can be tuned to an extent by slight changes in the cationic and/or anionic groups of IL or mixing with some organic liquid. Thus it is possible to design ILs or their mixtures containing organic liquids possessing desired properties. Experimental data on thermodynamic properties of IL mixtures are also of considerable interest for selecting appropriate mixtures in many industrial applications such as in the oil and gas industries [21] for flow assurance and oil recovery, in chemical industries [22] for the design and separation processes, in pharmaceutical and polymer industries [23] for solvent selection and emission control and in biotechnology for aggregation/separation of proteins [24]. These properties are also required for the proper design and operation of chemical reactions, pumps and heat transfer equipment [25], [26].

Cyclopentanone has the lowest auto-ignition reactivity of a number of biofuels and thus act as blending component to be used in spark-ignition internal-combustion engines [27]. Cyclopentanone and cyclohexanone have important applications in industries like synthesis of aromas and caprolactum intermediates or as final products in reaction medium; solvents in the synthesis of pharmaceuticals, insecticides, pesticides, flavor and fragrance reagents in pharmaceutical, agricultural and cosmetic industries [28], [29], [30]. In recent studies, we have reported excess molar volumes, VE, excess isentropic compressiblities, κSE, excess molar enthalpies, HE and excess heat capacities, CpE data of {1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i) + 1-butyl-3-methylimidazolium tetrafluoroborate (j)}; {1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i) + 1-ethyl-3-methylimidazolium tetrafluoroborate (j)}; {1-butyl-2,3-dimethylimidazolium tetrafluoroborate or 1-butyl-3-methylimidazolium tetrafluoroborate (i) + cyclopentanone or cyclohexanone (j)} mixtures. In continuation of our related studies, we extend our study to ternary mixtures and report densities, ρijk and speeds of sound, uijk, values of ternary mixtures containing {1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i) + 1-butyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium tetrafluoroborate (j) + cyclopentanone or cyclohexanone (k)}. The main aim of our work is to provide new experimental data on densities, ρijk, and speeds of sound, uijk of IL mixtures. Also it would be of interest to see how Graph and Prigogine-Flory-Patterson (PFP) theory describe the VijkE and (κSE)ijk results for ternary mixtures comprised of two ILs and one organic liquid.

Section snippets

Experimental

1-Butyl-2,3-dimethylimidazolium tetrafluoroborate [Bmmim][BF4]; (mass fraction: 0.990), 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4]; (mass fraction: 0.985) and 1-ethyl-3-methylimidazolium tetrafluoroborate [Emim][BF4]; (mass fraction: 0.990) were obtained from commercial sources and used after purification by vacuum treatment at residual pressure 5 × 10−2 Pa at 338 K to eliminate the water and other volatile compound traces. Cyclopentanone (CPO) (Fluka, mass fraction: 0.990) and

Results

Table 3 contains experimental values for densities, ρijk and speeds of sound, uijk of ternary {[Bmmim][BF4] (i) + [Bmim][BF4] or [Emim][BF4] (j) + CPO or CHO (k)} mixtures at temperatures (293.15, 298.15, 303.15 and 308.15) K. The measured ρijk and uijk values were utilized to determine their excess molar volumes, VijkE and isentropic compressibilities, (κS)ijk using equations:VijkE=i=ikxiMi(ρijk)-1-i=ikxiMi(ρi)-1(κS)ijk=(ρijkuijk2)-1where xi, Mi, ρi are the mole fraction, molar mass and density

Discussion

The ρ and u values for the purified [Bmmim][BF4], [Bmim][BF4], [Emim][BF4], CPO and CHO were taken from literature [33], [34], [35]. The deviations between measured and literature [44], [45], [46] ρ and u values for [Bmmim][BF4] at various temperatures were discussed in Ref. [33]. The experimental ρ and u values of [Bmim][BF4], [Emim][BF4], CPO and CHO are in agreement with their literature values [47], [48], [49], [50], [51], [52], [53], [54], [55], [56], [57], [58], [59], [60], [61], [62],

Graph theory

The thermodynamic, topological, IR and quantum mechanical studies of excess molar volumes, VE, excess isentropic compressibilities (κSE), excess heat capacities, CpE and excess molar enthalpies, HE values for {[Bmmim][BF4] (i) + [Bmim][BF4] or [Emim][BF4] (j), [Bmmim][BF4] or [Bmim][BF4] or [Emim][BF4] (i) + CPO or CHO (j)} mixtures in the literature [33], [34], [35], [56] have revealed that, (1) [Bmmim][BF4], [Bmim][BF4], [Emim][BF4] are characterized by cohesion forces between (a) hydrogen atom

Excess molar volumes

In the development of Prigogine-Flory-Patterson (PFP) theory of liquid mixtures, strong interactions among the constituent molecules are excluded. However, theory still provides in trusting correlation between the thermodynamic properties of liquid mixtures exhibiting strong molecular interactions. It was, therefore, of interest to predict VijkE and (κSE)ijk data of the present mixtures possessing strong interactions among the constituent molecules. According to PFP theory [68], excess molar

Conclusions

The excess molar volumes, VijkE and excess isentropic compressibility, (κSE)ijk values of the present mixtures have been determined using measured densities, ρijk and speeds of sound, uijk values. The excess properties, VijkE, (κSE)ijk have been correlated using Redlich-Kister equation to predict ternary adjustable parameters and standard deviations. The VijkE values for {[Bmmim][BF4] (i) + [Bmim][BF4] (j) + CPO (k)} and (κSE)ijk data of {[Bmmim][BF4] (i) + [Bmim][BF4] (j) + CPO or CHO (k)} mixtures

Acknowledgements

The authors are thankful to Mr. K. Chandrasekhar Reddy, SSBN College, Anantapur, for providing Gaussian-09 facility and C-DAC, PUNE, India for providing the computational work. V. K. Sharma is grateful to University Grant Commission (UGC), New Delhi for the award of SAP.

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