From Phases to Method (Models) Selection
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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 H2 + 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 4-7: Comparison of experimental values and different model with H2 + n-hexane mixture
Experimental values of VLE of hydrogen + n-hexane mixture have been published by Nichols et al. (1957). In figure 1, these experimental data at 377.6 K are compared with three models: Grayson-Streed, Peng-Robinson with BIP equal to zero and Peng-Robinson with BIP estimated by Moysan et al. . The cubic EoS without BIP strongly underpredicts the bubble pressure, and is clearly not recommended for hydrogen-containing mixtures. This effect is adequately corrected up to a liquid containing 50 % hydrogen with the BIP evaluated with Moysan procedure. The Grayson-Streed model  is adequate for bubble pressure prediction up to 30 % of hydrogen for this mixture at this temperature. The dew line is adequately predicted by the cubic EoS with the Moysan BIP. Grayson-Streed is less accurate. The same behaviour have been obtained at different temperatures.
A comparison with additional models has been reported by Ferrando and Ungerer (2007 ). They have shown that the error in the hydrogen solubility prediction in the liquid phase remains close to 5 % for all paraffins, except for the Grayson-Streed model that overpredicts the hydrogen solubility by more than 20 % when the solvent is heavier than C16 (figure 2). All theses models predict the hydrogen concentration in the vapour phase with less than 2 % error.
 NICHOLS W.B., REAMER H.H., SAGE B.H., Volumetric and phase behavior in the hydrogen-n-hexane system, AIChE Journal, 1957, 3, n°2, p. 262-267. http://dx.doi.org/10.1002/aic.690030223
 MOYSAN J.M., PARADOWSKI H., VIDAL J., Correlation Defines Phase-Equilibria for H2, Ch4 and N2 Mixes, Hydrocarbon Processing, 1985, 64, n°7, p. 73-76.
 GRAYSON H.G., STREED C.W., Vapor-Liquid Equilibria for high temperature, high pressure hydrogen-hydrocarbon systems, Frankfurt, p. 233-245, 1963.
 FERRANDO N., UNGERER P., Hydrogen/hydrocarbon phase equilibrium modelling with a cubic equation of state and a Monte Carlo method, Fluid Phase Equilibria, 2007, 254, n°1-2, p. 211-223. http://dx.doi.org/10.1016/j.fluid.2007.03.016