Thermophysical properties of the paramagnetic ionic liquid 1-butyl-3-methylimidazolium tetrachloroferrate over an extended range of temperature and pressure

Abstract

The paramagnetic ionic liquid 1-butyl-3-methylimidazolium tetrachloroferrate [BMIM][FeCl4] was subject to multiple high-precision thermophysical property measurements under both ambient and high pressure. Density ρ(p0,T) / kg·m−3 and speed of sound u(p0,T) / m·s−1 data at ambient pressure were recorded at temperatures T = (278.15 to 343.16) K using a DSA 5000 M combined vibrating tube densimeter and speed of sound analyser with a standard uncertainty of Δρ(p0,T) = ±0.001 kg·m−3 and Δu(p0,T) = ±0.1 m·s−1, respectively. High-pressure volumetric (p,ρ,T) data were measured on an Anton Paar DMA HPM vibrating tube densimeter at T = (273.16 to 413.15) K and at pressures up to p = 140 MPa with an estimated experimental relative combined average percentage deviation (APD) of Δρ(p,T) / ρ(p,T) = ±(0.01 to 0.08) %.The specific isobaric heat capacity cp(p0,T) / J·kg−1·K−1, a caloric property, was determined at T = (273.15 to 413.15) K with an uncertainty Δcp / cp = ±0.5 % using a Perkin Elmer Pyris 1 DSC differential scanning calorimeter. To gain knowledge of transport properties, the dynamic viscosity η(p0,T) / mPa·s at ambient pressure was recorded at T = (275.03 to 413.18) K by an Anton Paar SVM 3000 Stabinger viscometer and additionally an Anton Paar rheometer MCR 302 device with uncertainties of Δη / η = ±0.35 % and Δη / η = ±1 %, respectively.The obtained data were first correlated by empirical polynomial equations of state and further processed by the application of classic thermodynamic potentials to determine isothermal compressibility κT(p,T) / MPa−1, isobaric thermal expansivity αp(p,T) / K−1, thermal pressure coefficient γ(p,T) / MPa⋅K−1, internal pressure pint(p,T) / MPa, specific heat capacity at constant pressure cp(p,T) / J⋅kg−1⋅K−1 and at constant volume cv(p,T) / J⋅kg−1⋅K−1, the difference of isobaric and isochoric heat capacity (cp–cv)(p,T) / J⋅kg−1⋅K−1, speed of sound u(p,T) / m⋅s−1 and ultimately isentropic exponent κs(p,T).This work extends knowledge about the thermophysical properties of [BMIM][FeCl4] particularly to high temperatures and pressures.