Thermophysical properties of 1-butyl-4-methylpyridinium tetrafluoroborate Javid Safarov a,b,⇑ , Ismail Kul c , Waleed A. El-Awady b,d , Jürgen Nocke a , Astan Shahverdiyev b , Egon Hassel a a Institute of Technical Thermodynamics, University of Rostock, Albert-Einstein-Str. 2, D-18059 Rostock, Germany b Department of Heat and Refrigeration Techniques, Azerbaijan Technical University, H. Javid Avn. 25, AZ1073 Baku, Azerbaijan c Department of Chemistry and Biochemistry, Widener University, One University Place, Chester, PA 19013, USA d Mechanical Power Engineering Department, Mansoura Univeristy, Mansoura, Egypt article info Article history: Received 9 October 2011 Received in revised form 3 February 2012 Accepted 22 February 2012 Available online 3 March 2012 Keywords: Ionic liquid Density Viscosity Vibration tube densimeter Equation of state Isothermal compressibility Isobaric thermal expansibility Internal pressure abstract Thermophysical properties, {(p, q,T) at T = (283.15 to 393.15) K, pressures up to p = 100 MPa, and viscos- ity at T = (283.15 to 373.15) K and p = 0.101 MPa}, of 1-butyl-4-methylpyridinium tetrafluoroborate [b4mpy][BF 4 ] are reported. The measurements were carried out with a recently constructed Anton-Paar DMA HPM vibration-tube densimeter and a fully automated SVM 3000 Anton-Paar rotational Stabinger viscometer. The vibration-tube densimeter was calibrated using double-distilled water, methanol, tolu- ene, and aqueous NaCl solutions. An empirical equation of state for fitting of the (p, q,T) data of [b4mpy][BF 4 ] has been developed as a function of pressure and temperature to calculate the thermal properties of the ionic liquid (IL), such as isothermal compressibility, isobaric thermal expansibility, differences in isobaric and isochoric heat capacities, thermal pressure coefficient, and internal pressure. Internal pressure and the temperature coefficient of internal pressure data were used to make conclusions on the molecular characteristics of the IL. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Ionic liquids (ILs) are salts that are liquid at low temperatures (<100 °C) with very small vapor pressures [1–3]. They are used in various chemical industries. Determination of fundamental ther- mophysical and thermodynamic properties of ILs are necessary for the optimized design of chemical and separation processes as well as heat transfer media applications [4–6]. Thermodynamic properties of ILs have been recently reviewed [7,8]. This work is a continuation of our investigations in the field of (p, q,T) properties of ionic liquids [9–17]. Included are the (p, q,T) properties of [b4mpy][BF 4 ] at T = (283.15 to 393.15) K, at pressures up to p = 100 MPa, and viscosity measurements at T = (278.15 to 373.15) K, at pressures up to p = 0.101 MPa. The (p, q,T) properties were measured using a vibration tube densimeter and viscosity in a fully automated SVM 3000 Anton-Paar rotational Stabinger viscometer. A review of the literature [18–24] reveals that limited data on thermophysical properties (density, viscosity, etc.) exist at ambient pressure. This demonstrates that there is a need for careful (p, q,T) analysis of this IL at elevated pressures and temperatures. Heintz et al. [18,19], in 2001 measured the activity coefficients at infinite dilution c 1 i of 19 alkanes, alkenes, alkylbenzenes, alco- hols, acetone, acetonitrile, ethylacetate, alkylethers, and chlorome- thanes in the [b4mpy][BF 4 ] by gas chromatography using the ionic liquid as the stationary phase. The measurements were carried out at different temperatures between T = 313.1 K and T = 363.1 K. From the temperature dependence of the limiting activity coeffi- cients, partial molar excess enthalpies at infinite dilution H E;1 i of the organic solutes in the ionic liquids have been derived. The den- sity of the purified sample was measured at T = 298.15 K using the vibrating tube method. In 2002 Heintz et al. [20] studied the densities and viscosities for the system [b4mpy][BF 4 ] and methanol at T = (298.15, 313.15, and 323.15) K and ambient pressure using a vibrating-tube den- simeter DMA 602 and an Ubbelohde viscometer. The uncertainty in the density measurement was estimated to be ±2  10 5 g  cm 3 and in the viscosity measurements to be ±0.5%. Ortega et al. [21], in 2007 measured the behavior in solution of [b4mpy][BF 4 ] in water and in the first five alkanols of the series methanol to pentan-1-ol. The density measurements were made with an Anton Paar/Austria DMA-58 vibrating tube densimeter equipped with its own Peltier effect temperature control system, which maintained the temperature of the apparatus at ±0.01 K. The viscosity was measured with a Selecta ST-1000 rotational vis- cosimeter, equipped with a small-volume cell with a reading error of ±1% at the bottom of the scale, the reproducibility was 0.2%. The 0021-9614/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2012.02.018 ⇑ Corresponding author. Address: Lehrstuhl für Technische Thermodynamik, Universität Rostock, Albert-Einstein-Str. 2, D-18059 Rostock, Germany. Tel.: +49 381 4989415; fax: +49 381 4989402. E-mail address: javid.safarov@uni-rostock.de (J. Safarov). J. Chem. Thermodynamics 51 (2012) 82–87 Contents lists available at SciVerse ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct