Select thermodynamic models for process simulation
A Practical Guide to a Three Steps Methodology

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 (kij = 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 (kij = 0.00865).

image Figure 4 24: Comparison of experimental VLE and different models for a mixture of hexane + benzene at 343.15 K.

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