Fluid Phase Equilibria 332 (2012) 159–164 Contents lists available at SciVerse ScienceDirect Fluid Phase Equilibria jou rnal h omepage: www.elsevier.com/locate/fluid Experimental density and PC-SAFT modeling of Krytox ® (perfluoropolyether) at pressures to 275 MPa and temperatures to 533 K B.A. Bamgbade a,b,∗ , Y. Wu a,b , W.A. Burgess a , M.A. McHugh a,b a National Energy Technology Laboratory, Office of Research and Development, Department of Energy, Pittsburgh, PA 15236, USA b Department of Chemical and Life Science Engineering, Virginia Commonwealth University, Richmond, VA 23284, USA a r t i c l e i n f o Article history: Received 10 April 2012 Received in revised form 2 July 2012 Accepted 4 July 2012 Available online 14 July 2012 Keywords: Perfluoropolyether PFPE Krytox ® Demnum ® Lubricant High pressure Density PC-SAFT a b s t r a c t Density data from 298 to 533 K and to 275 MPa are reported for Krytox ® GPL 102, a poly(perfluoropropyl ether) (PFPE) with a CF 3 -branched fluoropropylether repeat group. The Tait equation fit to each density isotherm have mean absolute percent deviations (MAPD) between 0.11 and 0.30% with standard devia- tions (SD) not exceeding 0.20%. The perturbed-chain statistical associating fluid theory (PC-SAFT) fit to the density data has an MAPD of 0.67% and an SD of 0.67%. Likewise the PC-SAFT fit to previously reported density data of Demnum ® , a PFPE with an n-fluoropropylether repeat group, has an MAPD of 0.22% and a SD of 0.21% for Demnum ® S-20 and an MAPD of 0.27% with a SD of 0.14% for Demnum ® S-65. The trends exhibited by the PC-SAFT pure component parameters obtained from the fits of these three PFPEs are similar to those reported for linear and branched hydrocarbons with the same number of carbons. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Perfluoropolyethers (PFPEs) are a class of synthetic oils used in a variety of high-temperature lubricant and hydraulic fluid appli- cations [1–5]. The physical properties of PFPEs that make them excellent lubricants at extreme conditions include their low vapor pressure, low surface energy, good thermal stability, and non- flammability [3–5]. PFPEs only contain carbon, oxygen, and fluorine atoms and are inert to most chemicals including oxidizing agents, which makes PFPEs compatible in various chemical environments under extreme conditions [6,7]. Krytox ® GPL 102, a branched perfluoropolyether, manufac- tured by DuPont, is a fluorine end-capped, homopolymer of hexafluoropropylene epoxide, with a reported molecular weight of 1726 g/mol. The viscosity characteristics of Krytox ® GPL 102 closely mimic those of light oils produced in ultra-deep well formations and, therefore, this PFPE can be used as a representative standard for these light oils [8,9] There is a need for high-temperature, high- pressure density data for this Krytox ® oil, since the density is used to estimate the oil viscosity [10–12]. The present study reports ∗ Corresponding author at: Department of Chemical and Life Science Engineering, VCU, 601 West Main St., Richmond, VA 23284, USA. Tel.: +1 571 315 2199. E-mail address: bamgbadeba@vcu.edu (B.A. Bamgbade). experimental high-temperature, high-pressure Krytox ® GPL 102 density to temperatures of 533 K and pressures of 275 MPa. The density data are obtained using a variable-volume, high-pressure cell previously used to obtain density data for n-alkanes from pen- tane to eicosane [13,14]. The modified Tait equation [15] is fit to the Krytox ® density data obtained in this study to determine values for the two constants used with this equation. One of the parameters, B, has dimensions of pressure and varies with temperature and the other parameter, C, is a dimensionless constant whose value typically remains fixed for compounds from the same chemical family. The modified Tait equation is a reliable method to calculate liquid densities over wide ranges of temperature and pressure. The Perturbed-Chain Statistical Associating Fluid Theory (PC- SAFT), proposed by Gross and Sadowski [16], is also fit to Krytox ® density data to obtain values for the three pure component param- eters used with this equation. The PC-SAFT equation of state (EOS) represents the Helmholtz free energy as a sum of terms accounting for hard sphere repulsion, chain connectivity, dispersion inter- actions, and segment–segment association. In the present study the segment–segment association term is ignored since Krytox ® does not self-associate. Hence, the thermodynamic properties of non-associating fluids are predicted with the PC-SAFT EOS using parameters accounting for the number of segments in the molecule, m, the temperature-independent segment diameter, , and 0378-3812/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2012.07.008