Temperature and Pressure dependence of Branched Pentaerythritol Esters Density

Synthetic lubricants, which seem to be the most compatible oils with new refrigerants, are generally mixtures of pure components. At the moment, the literature reports only few works concerning experimental measurements and modeling of the volumetric properties for these fluids. The present study was conceived to measure the pFT behavior in the liquid phase of three branched pentaerythritol tetraalkyl esters (PEBMs), i.e. 2-methylbutyric ester oil (PEBM5), 2-methylpentanoic ester oil (PEBM6), and 2-methylhexanoic ester oil (PEBM7). They are commonly used as precursors for the commercial polyol ester (POE) lubricants. The measurements were executed by means of a vibrating tube densimeter along four isotherms, for T ) (283 to 343) K and p ) (0 to 17) MPa. The validation of the experimental procedure was made by measuring the density of liquid decane along six isotherms, for T ) (283 to 333) K and p ) (0 to 35) MPa, and comparing the results with the literature. A dedicated equation of state, derived from the Tait equation, was used to correlate the experimental density data for PEBMs and for decane. A procedure to evaluate saturation density was also defined.