Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Most of the industrial applications of ester-based synthetic lubricants are performed at medium and high pressures, but in the case of viscosity and density, the existing studies are carried out mainly at atmospheric pressure. Lubricants are normally composed by several compounds; hence, it is interesting to know how the pressure and the temperature affect the volumetric properties of mixed pentaerythritol esters (PE). In this work, the densities of two binary mixtures of pentaerythritol tetra(2-ethylhexanoate), PEB8, with pentaerythritol tetrapentanoate, PEC5, or with pentaerythritol tetraheptanoate, PEC7, and of one multicomponent mixture containing several pentaerythritol esters have been measured at temperatures from 278.15 K to 353.15 K and at pressures up to 45 MPa, using a vibrating tube densimeter. A correction factor, due to the viscosity of the sample, was applied to the density experimental values. The uncertainty in the measured densities is estimated to be 0.2 kgam-3. The composition of each mixture was chosen so that its kinematic viscosity at 313.15 K and atmospheric pressure was around 34a10-6 m2as-1 (ISO VG32). The experimental data have been used to study the behavior and the influence of temperature and pressure on the isothermal compressibility, the isobaric thermal expansion coefficient, and the internal pressure. In addition, according to Roland et al. [J. Chem. Phys. 2006, 125, 124508], for the three mixtures and four pure PEs, we have found that the viscosity is a unique function of TVc, where the exponent c is related to the steepness of the intermolecular repulsive potential.