## 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 4-3: Comparison of phase envelope predictions for the ethane + n-pentane mixture

Various models can be used to predict phase envelope. For the ethane + n-pentane mixture, the Reamer *et al.* [1] data of 1960 is available. Bubble and dew curves are represented on figure 1 with solid dots and empty dots respectively.

Given that ethane is supercritical at this temperature, and a critical point is observed on the diagram, only an equation of state (homogeneous approach) can be used.

The cubic Peng-Robinson EoS with binary interaction parameters (BIP) equal to zero gives a very good approximation of the complete envelope. There is a small under-prediction of the critical point but the general shape is correct. A small improvement can be made using the Nishiumi *et al.* [2] predicted BIP. An even better improvement is possible using fitted BIP obtained directly from experimental data.

Finally, a modern equation of state such as SAFT, in this case using the group contribution version (GC-SAFT), allows accurate representation of the whole envelope based only on predictive behaviour of molecules as described by Nguyen-Huynh et al. (2009)[3].

### References

[1] REAMER H.H., SAGE B.H., LACEY W.N., Phase Equilibria in Hydrocarbon Systems. Volumetric and Phase Behavior of the Ethane-n-Pentane System, *Journal of Chemical & Engineering Data*, 1960, **5**, n°1, p. 44-50. http://dx.doi.org/10.1021/je60005a012

[2] NISHIUMI H., ARAI T., TAKEUCHI K., Generalization of the binary parameter of the Peng and Robinson equation of state by component family, *Fluid Phase Equilibria*, 1988, **42**,p. 43-62. http://dx.doi.org/10.1016/0378-3812(88)80049-9

[3] NGUYEN-HUYNH D., PASSARELLO J.P., TOBALY P., In Situ Determination of Phase Equilibria of Methyl Benzoate plus Alkane Mixtures Using an Infrared Absorption Method. Comparison with Polar GC-SAFT Predictions, *Journal of Chemical and Engineering Data*, 2009, **54**, n°6, p. 1685-1691. http://dx.doi.org/10.1021/je800757j