Wilson/Redlich-Kwong model

Table 5.11 Binary interaction parameters of the Wilson/Redlich-Kwong model.

The most important aspect of the simulation is that the thermodynamic data of the chemicals be modeled correctly. It is necessary to decide what equation of state to use for the vapor phase (ideal gas, Redlich-Kwong-Soave, Peng-Robinson, etc.) and what model to use for liquid activity coefficients [ideal solutions, solubility parameters, Wilson equation, nonrandom two liquid (NRTL), UNIFAC, etc.]. See Sec. 4, Thermodynamics. It is necessary to consider mixtures of chemicals, and the interaction parameters must be predictable. The best case is to determine them from data, and the next-best case is to use correlations based on the molecular weight, structure, and normal boiling point. To validate the model, the computer results of vapor-liquid equilibria could be checked against experimental data to ensure their validity before the data are used in more complicated computer calculations. 

Firstly, we will examine the VLE of binary mixtures. The Wilson model is selected for liquid activity with Redlich-Kwong EOS for vapor phase. The predictions offered by Aspen Plus [9] are in agreement with experimental data [5], except... 

The fugacity coefficient is usually obtained by solving an equation of state (e.g., Peng-Robinson Redlich-Kwong). The activity coefficient is obtained from a liquid phase activity model such as Wilson or NRTL (see Walas, 1985). 

A better approach is to start from a particular model for g (T, P, x) A ), such as the Porter, Margules, or Wilson models introduced in 5.6. Here the A) are the model parameters, whose values are usually obtained by fits to phase-equilibrium data. We then select a PvTx model often a cubic is used. In this discussion, we consider the Redlich-Kwong equation ( 4.5.8). This model contains parameters a, b that depend on composition via some mixing rules ( 4.5.12). Our strategy is to find those mixing rules by matching the model to given by the PvTx equation. 

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