EXCESS ENTHALPY AND VAPOR-LIQUID EQUILIBRIA WITH THE MHV2 AND SOAVE MIXING RULES

Abstract

Calculations and predictions of excess enthalpy (H^E) and vapor-liquid equilibrium (VLE) were performed using the Gibbs energy mixing rules MHV2 and a modification of it by Soave. The Soave-Redlich-Kwong equation of state was combined with the UNIQUAC equation. Four sets of parameters estimated in the UNIQUAC model were used for each of seven binary systems: the first estimated from VLE data, the second and the third estimated from H^E data for two versions of the UNIQUAC equation, and the fourth estimated from both H^E and VLE data simultaneously. It was found that H^E calculations can be performed with the mixing rules; the average relative errors fell from around 200% for the conventional mixing rule to around 60% for MHV2 combined with DECHEMA UNIQUAC parameters and was as little as 20% when the UNIQUAC parameters had been estimated from H^E and VLE data simultaneously. However, the approach suffers from the same shortcomings as far as cross-prediction between H^E and VLE data is concerned, as does the UNIQUAC equation used alone. There is a discrepancy between values obtained with the mixing rule and those obtained with the UNIQUAC equation directly. This discrepancy is smaller for the Soave modification of the mixing rule.

Keywords:

• Equation of state
• Excess enthalpy
• Mixing rule
• Vapor-liquid equilibria

Notes

For temperature-dependent parameters: ν _ij  = ϑ _ij  + μ _ij (T − T ^Ref). The reference temperature (T ^Ref) used was 300 K for all systems.

The Source column refers to the volume, part, and page number in the DECHEMA data series where the experimental data may be found. The UNIQUAC parameters are found in Table II.

x = the Anderson modification was not applicable for these systems.

The Source column refers to the volume, part, and page number in the DECHEMA data series where the experimental data may be found. The UNIQUAC parameters are found in Table II.

x = the Anderson modification was not applicable for these systems.

The Source column refers to the volume, part, and page number in the DECHEMA data series (Gmehling et al., 1977–1996) where the experimental data may be found.

x = the Anderson modification was not applicable for these systems.

– = VLE calculations did not converge.