Theoretical Calculation of Henry Constants

In the statistical thermodynamic formulation (see Appendix A) the Henry constant is given by the ratio of the partition functions per unit volume for the adsorbed and vapor phases, with due correction for the difference in potential energy (/, //p. For an inert gas there are no internal degrees of freedom so, assuming classical behavior, this ratio of partition functions is equivalent to the configuration integral and one has the simple result 

TABLE 2.10. Comparison of Theoretical Dispersion Coefficients for Inert Gases in 5A Zeolite with Values derived from Henry Constant Data  

For zeolitic adsorbents consisting of discrete cages interconnected through relatively small windows, Eq. (2.21) assumes a very simple form if the adsorbed species can be regarded as retaining complete translational, rotational, and internal freedom within the free volume of the cage  

It is in principle possible to extend the theoretical calculation of Henry constants to more complex molecules where other contributions to the potential such as dipole and quadrupole energies, as well as restricted rotational freedom, must be considered. Such calculations have been attempted by 

TABLE 2.11. Values of and -d// Giving Temp ture Dependence of Henry Constants for Light Gases in 5A Zeolite According to Eq. (230)  

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