Example P08.01 Solubility of Anthracene and Phenanthrene in Benzene and

Ethanol (Ideal and Modified UNIFAC)

problem:

Calculate the solubility of the isomeric compounds anthracene and phenanthrene in benzene and ethanol at 25 °C assuming ideal behavior and using the group contribution method modified UNIFAC.

general

constants

and

definitions:

input data

Solution

First calculate the logarithm of the activity of the pure solid components anthracene and phenanthrene at 25°C:

In an ideal liquid mixture, the activity in the liquid phase is equal to the mole fraction (solubility).

In this case the nature of the solvent is not relevant. Note though, that this solubility is expressed as a mole fraction. Solvents with different molecular weight would yield different mass based solubilities.

In order to calculate the real liquid mixture behavior using mod. UNIFAC, the required information on the mixture and the UNIFAC parameters have to be defined:

This area contains the mod. UNIFAC parameters, group fragmentation, ...

mod. UNIFAC - Parameters:

This area contains the activity coefficient function for mod. UNIFAC

The activity coefficients of the two solutes in the two solvents can now easily be calculated at the ideal solubility (see above) and the solubility can be iteratively adjusted so that the activity is now equal to the ideal solubility:

Anthracene in Benzene:

initial value:

Phenanthrene in Benzene:

Anthracene in Ethanol:

Phenanthrene in Ethanol:

The results compare well with the experimental findings: