## Chapter 4:

From Phases to Method (Models) Selection

### Abstract

Read the abstract### Table of contents

See the table of contents### List of examples

- 4-1: Calculation of the condensation enthalpy of the acetone + water mixture with NRTL at a given pressure (1 bar)
- 4-2: Distribution coefficients in an ideal mixture (propane + n-pentane)
- 4-3: Comparison of phase envelope predictions for the ethane + n-pentane mixture
- 4-4: Behaviour of a methane + n-decane mixture and its models
- 4-5: Behaviour of the benzene + n-hexane mixture and its models
- 4-6: Calculation of the eutectic of para- and ortho-xylene
- 4-7: Comparison of experimental values and different model with H
_{2}+ n-hexane mixture - 4-8: Prediction of a heteroazeotrope with total liquid immiscibility
- 4-9: Formation of hydrates
- 4-10: Example of a vapour-liquid-liquid equilibrium of an acid gas system in the presence of water
- 4-11: VLE and LLE calculation of the methanol + n-hexane mixture

# Example 4-5: Behaviour of the benzene+ n-hexane mixture and its models

Benzene and hexane have very similar volatility but different polarity. As a result, a positive deviation from ideality is expected. In the figure, the Peng-Robinson equation of state is used and compared with the ideal mixture behaviour and the experimental data of Susarev and Chen (1963)[1]. The behaviour is nearly azeotropic, which the ideal mixture is unable to represent. The equation of state with zero interaction parameter catches the positive deviation, but using a small value for the binary interaction parameter (k_{ij} = 0.0074) improves the plot. For the purpose of comparison, the BIP has been calculated using the PPR78 predictive method of Jaubert et al.[2], giving a very similar result (k_{ij} = 0.00865).

### References

[1] SUSAREV M.P., CHEN S.T., Calculation of the Liquid-Vapor Equilibrium in Ternary Systems from Data for Binary Systems. The Benzene - n-Hexane - cyclo-Hexane System, *Zhurnal Fizicheskoi Khimii*, 1963, **37**, n°8, p. 1739-1744.

[2] JAUBERT J.N., MUTELET F., VLE predictions with the Peng-Robinson equation of state and temperature dependent kij calculated through a group contribution method, *Fluid Phase Equilibria*, 2004, **224**, p. 285-304. http://dx.doi.org/10.1016/j.fluid.2004.06.059