[C2mim][CH3SO3]─A Suitable New Heat Transfer Fluid? Part 2: Thermophysical Properties of Its Mixtures with Water

Abstract

Ionic liquids have proved to be excellent heat transfer fluids and alternatives to common HTFs used in industries for heat exchangers and other heat transfer equipment. However, its industrial utilization depends on the cost per kg of its production, to be competitive for industrial applications with biphenyl and diphenyl oxide, alkylated aromatics, and dimethyl polysiloxane oils, which degrade above 200 °C and possess some environmental problems. The efficiency of a heat transfer fluid depends on the fundamental thermophysical properties influencing convective heat transfer (density, heat capacity, thermal conductivity, and viscosity), as these properties are necessary to calculate the heat transfer coefficients for different heat exchanger geometries. In Part 1, the thermophysical properties of pure 1-ethyl-3-methylimidazolium methanesulfonate [C2mim][CH3SO3] (CAS no. 145022-45-3), (ECOENG 110), produced by BASF, under the trade name of Basionics ST35, with an assay ≥97% with ≤0.5% water and ≤2% chloride (Cl–), were presented, for temperatures slightly below room temperature and up to 355 K. In this paper, we report the thermophysical properties of mixtures of [C2mim][CH3SO3] with water, in the whole concentration range, at P = 0.1 MPa. The properties measured were density and speed of sound (293.15 < T/K < 343.15), viscosity, electrical and thermal conductivities, refractive index (293.15 < T/K < 353.15), and infinite dilution diffusion coefficient of the ionic liquid in water (298.15 K). The properties for the mixture like the isobaric expansion coefficient, the isentropic compressibility, apparent molar volumes, apparent molar isentropic compressions, and the thermodynamic excess properties, like excess molar volume, excess molar isobaric expansion and isentropic compression, excess viscosity, thermal conductivity, molar refraction, and infinite dilution diffusion coefficients of the cation, anion and other common anions in ionic liquids were obtained within this temperature range. The validity of the Walden relation for this ionic liquid was also determined. This amount of experimental information, in addition to recent molecular simulation studies available in the literature give a clear picture of the structure of these binary mixtures and the influence of composition and temperature, paving the way to a technological discussion of the possible application of these mixtures as new heat transfer fluids or battery electrolytes.