Elsevier

Fluid Phase Equilibria

Volume 406, 25 November 2015, Pages 156-162
Fluid Phase Equilibria

Phase equilibrium data for mixtures involving 1,1,2,3,3,3-hexafluoro-1-propene with either propane or n-butane between 312 and 343 K

https://doi.org/10.1016/j.fluid.2015.07.039Get rights and content

Abstract

Isothermal vapour–liquid equilibrium data are presented for binary mixtures of 1,1,2,3,3,3-hexafluoro-1-propene with either propane or n-butane in the (312–343) K temperature range. The experimental phase equilibrium data were measured using an apparatus based on the “static-analytic” method. The experimental data were correlated with a thermodynamic model comprising of the Peng–Robinson equation of state with the Mathias–Copeman alpha function, the Wong–Sandler mixing rule, and Non-Random Two-Liquid activity coefficient model. The model provided a very satisfactory correlation of the experimental data for both binary systems.

Introduction

Phase equilibrium data, for example vapour–liquid equilibrium (VLE) data, facilitate the design of multi-stage separation processes. Moreover, accurate experimental VLE data provide the basis necessary for the development and improvement of correlative and predictive thermodynamic models. Experimental phase behaviour involving mixtures of perfluorolefins and either paraffinic hydrocarbons or olefins are relatively scarce. On the contrary, we have published isothermal VLE data involving mixtures of 1,1,2,3,3,3-hexafluoro-1-propene (R1216 or HFP) with ethane [1], ethylene [2], propylene [3] and 1-butene [4]. The phase behaviour of these binary systems exhibits positive deviation from Raoult’s law. In addition, the R1216 + 1-butene binary system exhibits quasi-azeotropic behaviour at high concentrations of R1216 within the (313.05–343.10) K temperature range, indicative of the reluctance for mixing between the perfluorolefin and olefin molecules of relatively similar carbon chain lengths. This aversion to mixing was not entirely unexpected as liquid–liquid immiscibility has been observed for mixtures of longer chain perfluoroparaffins and short chain paraffins; e.g. n-butane + decafluorobutane and propane + octafluoropropane [5], [6]. Additionally, de Melo et al. compiled a list tabulating sources of liquid–liquid solubility data for perfluoroalkanes + alkane systems available in open literature [7]. Furthermore, it is interesting to note that a small change in the chain length of the alkane can have a remarkable effect on the phase behaviour. For example, the perfluorobutane + propane binary mixture presents a pressure-maximum azeotrope at high concentrations of propane in the temperature range of (313–343) K, whereas the perfluorobutane + ethane mixture exhibits no azeotrope over the extended temperature range of (263–353) K [8], [9]. In this work, we present isothermal VLE data for mixtures of R1216 with two short-chain paraffins, namely propane (R290) and n-butane (R600), from (312 to 343) K. The experimental VLE data were measured using an apparatus based on the “static-analytic” method. To the best of our knowledge VLE data for these systems have not been published in open literature, thus, the VLE measurements presented herein constitute new data. The new isothermal VLE data were correlated by coupling the Peng–Robinson (PR) equation of state (EoS) [10], Wong–Sandler (WS) mixing rule [11], and Non-Random Two Liquid (NRTL) activity coefficient model [12].

Section snippets

Materials

1,1,2,3,3,3-Hexafluoro-1-propene (C3F6, CAS number: 116-15-4) was supplied by the South African Nuclear Energy Corporation (NECSA, South Africa) with a certified purity greater than 0.999 in volume fraction. Propane (C3H8, CAS number: 74-98-6) was supplied by Messer Griesheim (France) with a certified purity greater than 0.9995 in mass fraction. n-Butane (C4H10, CAS number: 106-97-8) was supplied by Air Products (France) with a certified purity greater than 0.9995 in mass fraction. All

Results and discussion

Experimental vapour pressure data for propane and n-butane are reported in Table 2, the P–T data were modelled using the PR EoS with the MC alpha function. Vapour pressure data for R1216 were reported in our previous work [18]. Table 1 lists the MC parameters for R1216, propane and n-butane. Table 2 lists the experimental vapour pressure data for propane and n-butane, and the respective reference pressure values from REFPROP [19]. The resulting AADs for pressure are 0.004 and 0.001 MPa for

Conclusion

Vapour pressure data are reported for propane and n-butane. Vapour–liquid equilibrium data are presented for two binary systems, propane + R1216 and R1216 + n-butane, at three temperatures within the (312–343) K range. The data were measured using a “static-analytic” method using two ROLSIs. The expanded uncertainties on average are estimated as: U(T) = 0.03 K, U(P) = 0.004 MPa, U(x1) = 0.007 and U(y1) = 0.007. The data are well correlated with the PR EoS (MC alpha function) coupled with the WS mixing rule

Acknowledgement

This work is based upon research supported by the National Research Foundation of South Africa under the South African Research Chair Initiative of the Department of Science and Technology.

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