Chiyen, Kaleng Jim.
Abstract:
Modifications were undertaken to a static high pressure vapour-liquid equilibrium (VLE)
apparatus described by Naidoo [2004]. The alterations were made to improve the sample
analysis technique. These modifications included the incorporation of the ROLSITM sampling
device into the equilibrium cell, a re-design of the air bath which improved the temperature
profile and further alterations described in the text.
The equipment has an operating temperature range of 278.15 K to 473.15 K and pressure range
of absolute vacuum to 150 bars. The apparatus consisted of an agitated cell in an air-bath. The
uncertainties in the temperature and pressure measurements were ±0.02 K and ±4 kPa
respectively. A Shimadzu Gas Chromatograph, Model 2010 was used for sample analysis.
An initial test of the apparatus was carried out to measure the pure component vapour pressure
data for propane and ethane in the temperature range of 279.24 – 360.18K and the results
concurred with literature data (absolute relative deviation <0.153%)
The experimental procedure used in this study was developed from the technique used by
Ramjugernath [2000], with some minor changes implemented only to achieve some
requirements for problems encountered during the project.
Isothermal binary measurements for the hexafluoroethane (R116) + propane system were used
as test system to investigate the accuracy and reliability of the equipment. Three binary
isotherms were measured at 291.22 K, 296.23 K and 308.21 K. The measured data compared
well with literature data.
Particular attention was placed on the fluorinated hydrocarbons. Specific properties of
fluorinated hydrocarbons give them many applications in industry, such as solvents,
refrigerants, propellants, anaesthetics, etc. Hence, a phase equilibria study of a fluorinated
hydrocarbons system was carried out in this project.
The commissioning of the equipment was successfully undertaken and the equipment was
found to be efficient and reliable. As a consequence measurements were made on the
hexafluoropropylene oxide (HFPO) + ethane system. No data has been previously published in
literature for this system. Measurements were undertaken at five different temperatures, 283.15 K, 290.15 K, 298.15 K, 308.15 K and 318.15 K. The isotherms were chosen in order to have
measurements below and above the critical temperature of ethane, in order to see the transition
at the critical temperature.
The experimental data were modelled via the direct (phi-phi) method. The Peng-Robinson
equation of state was applied, including the Mathias-Copeman alpha correlation with the Wong-
Sandler mixing rules incorporating the NRTL activity coefficient model. Good agreement was
found between the correlated and the measured data.
