Elsevier

Fluid Phase Equilibria

Volume 316, 25 February 2012, Pages 141-146
Fluid Phase Equilibria

Vapor–liquid equilibrium data for the dimethyl ether (RE170) + decafluorobutane (R3-1-10) system at temperatures from 313.28 to 392.83 K and pressures up to 4.9 MPa

https://doi.org/10.1016/j.fluid.2011.11.026Get rights and content

Abstract

Isothermal vapour–liquid equilibrium data have been measured for the RE170 + R3-1-10 binary system at nine temperatures between 313.28 and 392.83 K, and pressures between 0.57 and 4.9 MPa. The experimental method used in this work is of the static-analytic type, taking advantage of two pneumatic capillary samplers (ROLSI™, Armines’ patent) developed in the CEP/TEP laboratory. The data were obtained with accuracies within ±0.02 K, ±0.0006 MPa and ±0.009 for molar compositions. The particularity of this system is to present an azeotrope. The isothermal P, x, y data are well represented with the Peng and Robinson equation of state using the Mathias Copeman alpha function and the Wong–Sandler mixing rules involving the NRTL gE model.

Highlights

► We determine new experimental data concerning RE170 + R3-1-10 binary system. ► An equipment based on “static analytic” method with phase sampling. ► Cubic equation of state is used for the data treatment. ► Data and model are used to generate complete phase diagram of the system and identify azeotropic behavior.

Introduction

In the recent year, organic Rankine cycle (ORC) has become a promising technology for the conversion of low or medium temperature heat to electricity. The heat source can be of various origins but one interesting source is the waste stream of industrial processes. The temperature is below 200 °C. Initially, the working fluids used in Rankine cycle engines was steam but is generally apply for higher temperature Rankine Engines. Steam is not very expensive and chemically stable. But concerning low grade energy application [1], steam is not the best choice of working fluid. Moreover, the selection of the working fluids is very important for the use of ROC process. A bad choice leads to a low thermodynamic efficiency and technico-economy [2]. The thermodynamic properties for a good fluid are [1], [2]:

  • Critical temperature value must be above the highest temperature of the cycle

  • Not excessive vapour pressure but it must be above atmospheric pressure at the minimum temperature of the cycle (condensing pressure)

  • Triple point value is below the minimum ambient temperature to avoid solidification

  • Small specific volume, low viscosity at the liquid phase,

  • No ozone depletion potential (ODP) and law global warming potential (GWP)

  • Non corrosivity and compatibility with common system materials

  • The fluid should be chemical stable (no thermal decomposition)

  • Non toxicity, non flammability

  • Good lubrification properties

  • Low cost and available in large quantity

In this communication we propose to determine the thermodynamic properties (phase equilibria) of the possible candidate which is a mixture of dimethyl ether (RE170) and perfluorobutane (R3-1-10). The critical properties and CAS numbers of the two fluids are presented in Table 1. We can see that the values of their critical temperature can be adequate for ORC. The GWP (100 years) of the R3-1-10 is 7000 [4] or [5]. The GWP of RE170 is equal to 1 [5]. Otherwise, the R3-1-10 is non flammable which is not the case of the RE170.

The new enclosed experimental results are fitted using the Peng and Robinson equation of state (PR EoS). This work reveals that the binary system can be classified as type I according to Scott and van Konynenburg classification [6] with a positive deviation to ideality involving an azeotrope. At the knowledge of the authors, it exists not data in the open literature.

Section snippets

Materials

RE170 was obtained from Arkema (France) with a certified purity higher than 99.9 vol.%. R3-1-10 was purchased from Pelchem (South Africa) and has a certified purity higher than 98 vol.%. RE170 was carefully degassed before use to remove uncondensed gases.

Apparatus

The apparatus used in this work is based on a static-analytic method with liquid and vapour phase sampling. This apparatus is similar to that described by Valtz et al. [7], [8], [9], [10].

The equilibrium cell is contained in a liquid thermostatic

Vapour pressures

The vapour pressures of pure R3-1-10 and RE170 were measured between 263.15 and 395.74 K (see Table 2). The Mathias-Copeman coefficients adjusted on these experimental data are reported in Table 3. Concerning the perfluorobutane, the bias and the absolute relative deviation are respectively −0.05% and 0.22%. Concerning the Dimethyl ether, the bias and the absolute relative deviation are respectively −0.002% and 0.05%. The reason of higher deviation with the perfluorobutane can be attributed to

Conclusion

In this paper we present VLE data for the system RE170 + R3-1-10 at 9 temperatures that are either below or above the R3-1-10 critical temperature. We used a static-analytic method to obtain our experimental data. We chose the Peng and Robinson EoS, with the Mathias-Copeman alpha function and the Wong–Sandler mixing rules involving the NRTL model to fit experimental data. The experimental results are given with following accuracies: ±0.02 K, ±0.0006 MPa and ±0.009 for vapour and liquid mole

List of symbols

    a

    parameter of the equation of state (energy parameter [J m3 mol−2])

    A

    molar Helmhotz energy [J]

    b

    parameter of the equation of state (molar co volume parameter [m3 mol−1])

    c

    Mathias-Copeman coefficient

    C

    numerical constant, Eq. (3)

    F

    objective function

    g

    molar Gibbs energy [J mol−1]

    n

    number of moles

    P

    pressure [MPa]

    R

    gas constant [J mol−1 K−1]

    T

    temperature [K]

    x

    liquid mole fraction

    y

    vapour mole fraction

    Greek letters

    αij

    NRTL model non-random parameter (Eq. (5))

    τij

    NRTL model binary interaction parameter (Eq. (5)), [J mol−1]

    ω

    acentric

Acknowledgement

The authors would also like to thank Pelchem and NECSA (South Africa) who supplied the perfluorobutane.

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