(335ac) Vapor-Liquid Equilibria For Binary Systems Consisting Of Hexafluoroethane (R116) With Ethane And Propane

Authors: 
Ramjugernath, D., University of KwaZulu-Natal
Valtz, A., Mines ParisTech
Richon, D., MINES ParisTech, CEP/TEP - Centre Énergétique et Procédés


There is a developing interest from Industry in the potential of fluorinated hydrocarbons as solvents for separation. In this study, the potential of R116 as an extractive solvent in the separation of light hydrocarbons was investigated. To this effect vapour-liquid equilibrium measurements were undertaken for the two binary systems, viz. R116 + ethane and R116 + propane, at temperatures above and below the critical temperature of R116. As an extension of the contribution tables for the predictive Soave-Redlich-Kwong (PSRK) model, the contribution of R116 as a single molecule was also computed. From a thermodynamic point of view, R116 + propane and R116 + ethane are classified as Type I systems according to the classification of van Konynenburg and Scott. Moreover, the peculiarity of the R116 + ethane binary system is to present an azeotrope, whereas for the R116 + propane binary system there is a quasi azeotropic behaviour in the very dilute composition in propane. High pressure vapor-liquid equilibria (VLE) data were measured for the binary system R116 + propane at 5 isotherms viz. 263.15, 283.15, 291.15, 296.15 and 308.15 K. The data was measured on a static-analytic apparatus, with analysis of the equilibrium phases via two pneumatic capillary samplers (RolsiTM, Armines patent). The apparatus and the samplers were developed in the CEP/TEP laboratory. The VLE data for the R116 + propane system was modelled using the phi-phi method, incorporating the Peng-Robinson EOS with Wong and Sandler mixing rules. The critical point locus for the system was predicted from the correlated data. The data was also correlated with the PSRK EOS and a group contribution was determined for hexafluoroethane as a single molecule. The VLE for the binary system R116 + ethane was predicted for three isotherms (273.15, 288.15 and 291.15K) using the PSRK EOS with the group contribution parameters obtained for R116. Experimental measurements for the binary system at the three respective temperatures were also undertaken to verify and improve the predictions of the PSRK EOS.