Excess Enthalpy and Vapor-Liquid Equilibria with the MHV2 and Soave Mixing Rules

Artikel i vetenskaplig tidskrift, 2011

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.