Binary vapour-liquid equilibrium data for C7 and C9 straight-chain perfluorocarbons with ethylene

Abstract

Experimental vapour-liquid equilibrium data are reported for the binary systems of ethylene + perfluoro-n-heptane and ethylene + perfluoro-n-nonane. Isothermal measurements were performed within the temperature range of (293–354) K, and at pressures up to 9 MPa, using an apparatus based on the “static-analytic” method. The experimental data were correlated using the Peng–Robinson equation of state utilizing either the van der Waals mixing rule or the Wong–Sandler mixing rule coupled with the Non-Random Two-Liquid (NRTL) activity coefficient model. Both model combinations provided adequate representation of the experimental data, with the model involving the Wong-Sandler mixing rule providing a slightly better fit.

Introduction

Perfluorocarbons (PFCs) have been noted to exhibit interesting physicochemical properties due to the high intramolecular and low intermolecular forces that characterize them [1]. At room temperature common perfluoro-n-alkanes can be grouped into gaseous and liquid compounds based on their boiling points. Perfluorocarbon organic molecules are useful in variety of applications and fields, ranging from environmental sciences (potential replacements for chlorofluorocarbons), material sciences (precursors in the production of polytetrafluoroethylene) to medical sciences (blood substitutes) [1], [2], [3], [4]. Additionally, it has been noted that the solubility of certain surfactant molecules in supercritical carbon dioxide increases by the presence of perfluorinated chains [5], [6]. PFCs are non-toxic and exhibit low ozone depleting potentials (ODPs). On the contrary, they do possess high Global warming potentials (GWPs), which limits the use of PFCs in industry to longer carbon chains variants. However, both the density and the viscosity of PFCs increase with an increase in the carbon chain length of the molecule; an increase in such properties can reduce the efficiency of multi-phase separation processes. This work forms part of a large research programme, currently being undertaken, which concerns the investigation of thermodynamic and thermophysical properties of pure fluorocarbons (hexafluoropropylene and hexafluoropropylene oxide) [7], [8], mixtures of fluorocarbons (hexafluoropropylene, hexafluoropropylene oxide, hexafluoroethane, tetrafluoroethene, and octafluorocyclobutane) [9], [10], [11], [12], and mixtures of fluorocarbons (decafluorobutane, hexafluoroethane, hexafluoropropylene, hexafluoropropylene oxide, perfluoropropane, decafluorobutane, perfluorohexane, and perfluorooctane) with either hydrocarbons (methane, ethane, ethylene, propane, propylene, and 1-butene) or non-hydrocarbons (carbon dioxide, carbon monoxide, nitric oxide, and hydrogen sulphide) [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27]. In a previous paper, vapour-liquid equilibrium (VLE) data for the binary system of ethylene + perfluoro-n-octane were reported [17]. The context of this work is to extend the current knowledge of phase behavior between PFCs and olefins. High-pressure (up to 9 MPa) isothermal VLE data were measured for the binary systems of ethylene with either perfluoro-n-heptane or perfluoro-n-nonane. The experimental VLE data were modelled using the Peng-Robinson (PR) [28] Equation of State (EoS) with either the van der Waals mixing rule or the Wong-Sandler (WS) mixing rule [29] coupled with the Non-Random Two Liquid (NRTL) activity coefficient model [30]. To the best of our knowledge the data measured in this study is novel and we have not been able to find phase data for these systems in the literature.