Fluid Phase Equilibria 228–229 (2005) 367–371
Phase behavior studies of a perfluoropolyether
in high-pressure carbon dioxide
Teresa Casimiro
a
, Alireza Shariati
b
, Cor J. Peters
b
,
Manuel Nunes da Ponte
a
, Ana Aguiar-Ricardo
a,∗
a
REQUIMTE/CQFB, Departamento de Qu´ ımica, Faculdade de Ciˆ encias e Technologia,
Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
b
Laboratory of Applied Thermodynamics and Phase Equilibria, Faculty of Applied Sciences,
Delft University of Technology, The Netherlands
Abstract
This work presents vapor–liquid equilibrium measurements for the binary system carbon dioxide-Krytox 157 FSL, a commercial perfluo-
ropolyether carboxylic acid terminated. The measurements were carried out between 313.15 and 343.15 K and at pressures up to 18 MPa in a
static analytical apparatus. Krytox showed high miscibility with CO
2
and it was possible to define the contour of the vapor–liquid equilibrium
region as well the determination of the critical line. The Sanchez–Lacombe EOS was able to calculate the liquid equilibrium composition of
the CO
2
+ Krytox binary system quite adequately, by fitting two temperature dependent interaction parameters, although it did not predict
any solubility for the vapor phase. Due to lack of thermodynamic data, the characteristic parameters of Krytox were estimated by a method
proposed by Sanchez and Lacombe, using a known heat of vaporization, a vapor pressure and a liquid specific volume at 313 K.
© 2004 Elsevier B.V. All rights reserved.
Keywords: PFPE; Vapor–liquid equilibria; Sanchez–Lacombe; Equation of state
1. Introduction
Krytox, a commercially available carboxylic acid termi-
nated perfluoropolyether (Mn2500) from DuPont is typically
used in industry as lubricant oils for surface pre-treatment of
discs and of stone surfaces against corrosion [1].
Due to the low critical pressure and temperature of car-
bon dioxide, an atomization process from a supercritical CO
2
solution is an alternative method to CFC solvents for the ap-
plication of this protective material [2]. Recently a new in-
DOI of original article:10.1016/j.fluid.2004.07.016.
Please note this article was also published in a recent regular article of
Fluid Phase Equilibria Vol 224/2 pgs 257–261, while it should have been
part of the PPEPPD 2004 proceedings special issue in which it is now pub-
lished. Please use the original article citation. The Publisher regrets any
inconvenience this may cause.
∗
Corresponding author. Tel.: +351 212 949 448; fax: +351 212 948 385.
E-mail address: aar@dq.fct.unl.pt (A. Aguiar-Ricardo).
teresting application was discovered. Krytox has shown to
be an effective pseudo-graph stabilizer in the polymerization
of acrylated monomers such as methyl methacrylate (MMA)
[3–5] and diethylene glycol dimethacrylate (DEGDMA) [6].
In opposition to other stabilizers it is possible to extract com-
pletely Krytox at the end of the reaction by washing the poly-
mer with fresh high-pressure CO
2
.
Newman et al. [7] measured cloud point curves of mixtures
of different molar masses of Krytox in supercritical CO
2
.
However, their data is essentially of Krytox derivates, am-
phiphiles obtained by neutralizing the terminal acid to form
sodium, potassium and calcium salts that are compared with
only three data points of Krytox oil in CO
2
. No data for the
polymer-rich phase was found.
The study of the phase behavior of the binary system CO
2
+ Krytox, in particular the contours of the homogeneous
one-phase region and the compositions of the phases in
equilibrium in the two-phase region, is fundamental for the
0378-3812/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.fluid.2005.03.006