Vapour–liquid equilibrium measurements and correlation for the pentafluoroethane (R125) + n-butane (R600) system
Introduction
In the search for alternative refrigerants with zero ozone depletion potential (ODP) and low global warming potential (GWP), mixtures formed by hydrocarbons (HC) and hydrofluorocarbons (HFC) seem to be very interesting. Following our studies on vapour–liquid equilibria (VLE) of several HC + HFC systems, such as 1,1,1,2-tetrafluoroethane (R134a) + isobutane (R600a), R600a + 1,1,1,3,3,3-hexafluoropropane (R236fa) [1], 1,1,1-trifluoroethane (R143a) + propane (R290), R290 + R134a [2], R290 + R245fa [3], R290 + R236fa [4], R290 + 1,1,1,2,3,3-hexafluoropropane (R236ea) [5], R600a + 1,1,1,3,3-pentafluoropropane (R245fa) [6], R290 + 1,1,1,2,3,3,3-heptafluoropropane (R227ea) [7], pentafluoropropane (R125) + R290 [8], difluoromethane (R32) + R290 [9] and R32 + n-butane (R600) [10], and on liquid–liquid equilibria (LLE) of R32 + R290 [11], R32 + R600 [12] and R125 + R600 system [13], vapour–liquid equilibria (VLE) data for this last system were measured at temperatures of 278.15 and 298.15 K and presented in this work. The experimental data were used for a comparative analysis of the correlating ability of few equations of state with various mixing rules for this strongly non-ideal system.
Section snippets
Materials
R125 (pentafluoroethane, C2HF5) was provided by Solvay, with a declared purity >99.9% and R600 (n-butane, C4H10) by Aldrich with a stated purity >99%. After the elimination of the non-condensable gases, neither thermal conductivity nor flame ionization (FID) detectors of a gas chromatograph identified any impurities; a Porapak Q column with a length of 2 m and an external diameter of 1/8 in. was used. All samples were used with no further purification.
Apparatus
VLE measurements were performed using the
Results and discussion
The VLE (T–P–x–y) were measured at two isotherms (T = 278.15 and 298.15 K) and the experimental data are presented in Table 1 and Fig. 1. Within this temperature range the liquid phase is completely miscible and zeotropic over the whole composition range but with a strong positive deviation from the Raoult's law. For this system, the appearance of a partial miscibility of liquid phase was observed at temperatures below 216 K [13]. In [13], 24 solubility P–T–x data for the R125 + R600 system were
Conclusions
Twenty six vapour–liquid equilibria experimental data were measured at two temperatures (278.15 and 298.15 K). The data show a strong positive deviation from the Raoult's law, even if the system is zeotropic.
Several models were considered to represent the system behaviour. The RKS, the PR and the CSD EoS, together with the classical mixing rule, did not prove to work successfully. An improvement was found using a composition dependent mixing rule with the same EoS. The best results were obtained
Acknowledgments
Mauro Scattolini is gratefully acknowledged for his help in the measurements. Roman Stryjek is indebted to CNR-ITC in Padova for financial support during his visit.
References (25)
- et al.
Fluid Phase Equil.
(1998) - et al.
J. Chem. Thermodyn.
(2000) - et al.
Fluid Phase Equil.
(2000) - et al.
Fluid Phase Equil.
(2001) - et al.
Fluid Phase Equil.
(2002) - et al.
Fluid Phase Equil.
(2002) - et al.
Fluid Phase Equil.
(2003) - et al.
Fluid Phase Equil.
(2003) - et al.
Fluid Phase Equil.
(2004) Chem. Eng. Sci.
(1972)