Excess heat capacities of (binary + ternary) mixtures containing [emim][BF4] and organic liquids

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Highlights

  • The CPE and CPEijk data have been measured over entire composition range at four temperatures.

  • The observed data have been fitted to Redlich–Kister equation.

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

  • The values determined by Graph theory compare well with experimental values.

Abstract

The excess heat capacities, CPE and CPEijk (calculated from the measured molar heat capacities, Cp data) of binary 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + pyrrolidin-2-one or 1-methylpyrrolidin-2-one or pyridine (j); pyrrolidin-2-one (i) + pyridine (j) and ternary 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + pyrrolidin-2-one or 1-methylpyrrolidin-2-one (j) + pyridine (k) mixtures have been measured as a function of composition at T = (293.15, 298.15, 303.15 and 308.15) K and 0.1 MPa using micro differential scanning calorimeter. The CPEijk values for the present ternary mixtures are positive over entire range of composition. The CPE and CPEijk data have been fitted to Redlich–Kister equation to compute binary and ternary adjustable parameters along with their standard deviations. The topology of the constituent molecules (Graph theory) has been utilized to obtain the expressions that describe well the CPE and CPEijk data of the present mixtures. It has been observed that Graph theory describes well the CPE and CPEijk data of the binary as well as ternary mixtures.

Introduction

Large quantities of solvents are used for numerous processes in chemical and related industries. Consequently, the challenge of non-harmful solvents because of new environmental regulations has promoted a great development of innovative products to protect environment. The appealing set of properties [1], [2], [3], [4] exhibited by ionic liquids suggests the possible use of ionic liquids or their mixtures or their mixtures with organic liquids in a variety of applications [5], [6], [7]. For thermo chemical applications, one of the thermodynamic properties of liquid mixture is heat capacity. Heat capacity data are required for the design of heat exchanger equipment in the gas treating processes. Also this property is most needed in the design of processes and equipment in the part where heat transfer is important [8], [9], [10]. Thus, heat capacity data of ionic liquid mixtures may be of great value in chemical industries and also from theoretical point of view. In continuation of our studies on thermodynamic properties like excess molar volumes, VE, excess isentropic compressibilities, κSE and excess molar enthalpies, HE of binary or ternary mixtures containing 1-ethyl-3-methylimidazolium tetrafluoroborate as one of the component [11], [12], [13], we report here excess heat capacities, CPE data of 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + pyrrolidin-2-one or 1-methyl pyrrolidin-2-one (j) + pyridine (k) and their sub-binary 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + pyrrolidin-2-one or 1-methyl pyrrolidin-2-one or pyridine (j); pyrrolidin-2-one (i) + pyridine (j) mixtures. Graph theory (which deals with the topology of the constituents of the molecules) has recently been successfully utilized [14], [15], [16] to predict excess heat capacities, CPE data of the binary liquid mixtures. It would be of great interest to see how Graph theory describes CPE data of the present binary as well as ternary liquid mixtures containing ionic liquid as one of the constituent molecules. These considerations prompted us to measure CPE data of the investigated (binary + ternary) mixtures.

Section snippets

Experimental

1-Ethyl-3-methylimidazolium tetrafluoroborate [emim][BF4] (mass fraction: 0.980) was used without further purification. The water content in ionic liquid was regularly checked using Karl Fischer titration [17] and found to be less than 318 ppm. Pyrrolidin-2-one (2-Py) (mass fraction: 0.993) was purified by vacuum distillation over calcium oxide [18], 1-methyl pyrrolidin-2-one (NMP) [mass fraction: 0.992) was purified by fractionally distilled under reduced pressure [19], and Pyridine (Py) [mass

Results

The molar heat capacities, Cp and (CP)ijk of [emim][BF4] (i) + 2-Py or NMP or Py (j); 2-Py (i) + Py (j) binary and [emim][BF4] (i) + 2-Py or NMP (j) + Py (k) ternary mixtures measured over entire mole fraction range at T = (293.15, 298.15, 303.15, 308.15) K are listed in TABLE 2, TABLE 3, respectively.

The excess heat capacities, CPE and (CPE)ijk data of the present (binary + ternary) mixtures were determined from the following relationsCPE=CP-i=ijxi(CP)i,(CPE)ijk=(CP)ijk-i=ikxi(CP)i,where Cp, (CP)ijk, (Cp)

Discussion

We are unaware of any CPE and (CPE)ijk data of the present (binary + ternary) mixtures at T = (293.15, 298.15, 303.15 and 308.15) K that are available in literature for comparison with measured results. The CPE values for [emim][BF4] (i) + NMP (j) mixture are negative over entire range of composition. There is a region of negative CPE at low mole fraction of [emim][BF4], passing through a minima and then CPE increases, becoming positive and presenting maxima at high mole fraction of [emim][BF4] for

Excess heat capacities of binary mixtures

Thermodynamic and topological analysis of VE, κSE and HE data of [emim][BF4] (i) + 2-Py or NMP or Py (j) binary mixtures [11], [25] have shown that while [emim][BF4] exist as a monomer; 2-Py, NMP and Py exist as dimer. 2-Py (i) + Py (j) mixture formation was then considered to be comprised of the processes, (1) formation of in  jn (n = 2) contacts; (2) unlike contact formation rupture self association of in and jn to form their respective monomer and leads to increase the randomness; (3) i and j

Conclusion

Molar heat capacities, CP and (CP)ijk of studied (binary + ternary) mixtures containing 1-ethyl-3-methylimidazolium tetrafluoroborate as one of the component were measured with a micro differential scanning calorimeter at T = (293.15, 298.15, 303.15, 308.15) K. Excess heat capacities, CPE and (CPE)ijk have been utilized using the Redlich–Kister equations for the composition dependence to represent the measured CP and (CP)ijk data. The CPE and (CPE)ijk values predicted by employing the topology of

Acknowledgements

S. Bhagour is grateful to University Grants Commission (UGC), New Delhi for the award of Project fellow. The Authors are also grateful to the Head of Chemistry Department and authorities of M. D. University, Rohtak, for providing research facilities.

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