Reaction submodel for HF hexamerization

You must provide an HF reaction submodel to model the reaction equilibrium between the monomer and hexamer formations of HF in the vapor phase.

In the Fluids Library, we provide the RXHF reaction submodel that uses the reaction equilibrium kinetics from Long, Hildebrand, and Morrell1. You can use this reaction submodel in your HF Fluid Types if you do not have reaction equilibrium data of your own. You can also use this reaction submodel as a starting point if you want to build your own HF reaction submodel with customized reaction equilibrium data. The following documentation describes the basics of the RXHF reaction submodel.

The hexamerization equilibrium reaction is:

The following equation gives the corresponding chemical equilibrium constant (Keq) for this reaction, which is a function of temperature:

where

f1 is the fugacity coefficient of the monomer species

f6 is the fugacity coefficient of the hexamer species

y1 is the actual mole fraction of the monomer species

y6 is the actual mole fraction of the hexamer species

P is the total pressure

Currently, we use the fugacity coefficient values from the CompositionalState fluid state submodel. This allows us to rewrite the preceding equation as:

where

P is the total pressure in kPa

f1 and f6 are known values

Once we know the value of Keq, we can solve this equation to obtain the value for y1 and the corresponding value for y6.

We use the following equation from Long, Hildebrand, and Morrell1 to calculate the equilibrium constant for HF hexamerization:

where

Keq is the equilibrium constant in 1/(mmHg)5

T is the temperature in K

After we calculate the y1 and y6 compositions, we then calculate the HF monomer-hexamer mixture properties according to the mixing rules for the thermodynamic method that you select in the System list for the Fluid Type.