Henry constant theoretical calculation

In principle, the Henry constant may be predicted theoretically by evaluation of the configuration integral for an occluded molecule. Such calculations are subject to the considerable uncertainties implicit in theoretical potential calculations (17), and the utility of this approach is now limited to simple spherical molecules such as the inert gases (18, 19). A fair estimate of the standard entropy of sorption or of the value of K0 may, however, be obtained from a simple idealized model. 

Theoretical calculation based on the extremely high Henry s law constant. 

FIGURE 2.6. Comparison of experimenlal and theoretical Henry constants for An Kr, and Xe in 5A xeolile, calculated from the potential profiles derived from the London, Slater-Kirkwood and Kirkwood-Muiler equations [Eqs. 2.7)-(2.9)j. (From ref. 14 reproduced by permission of the National Research Council of Canada from the Canadian Journal of Chemistry. Volume 53, 1975.)... 

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... 

Results of an experimental study of the sorption of several hydrocarbons on NaX and NaY zeolites are summarized in Table 4.2 and Figure 4.7. For these species at all temperatures investigated the saturation capacity was found to be close to 3.0 molecules/cage so only two coefficients A2 and A2) are required in Eq. (4.5). The Henry constants were found from the limiting slopes of the isotherm at low pressure. Values of were then calculated by integration of the isotherms [Eq. (4.5)], and the values so obtained were matched to the theoretical expression ... 

The results of experimental studies of the sorption and diffusion of light hydrocarbons and some other simple nonpolar molecules in type-A zeolites are summarized and compared with reported data for similar molecules in H-chabazite. Henry s law constants and equilibrium isotherms for both zeolites are interpreted in terms of a simple theoretical model. Zeolitic diffusivitiesy measured over small differential concentration steps, show a pronounced increase with sorbate concentration. This effect can be accounted for by the nonlinearity of the isotherms and the intrinsic mobilities are essentially independent of concentration. Activation energies for diffusion, calculated from the temperature dependence of the intrinsic mobilitieSy show a clear correlation with critical diameter. For the simpler moleculeSy transition state theory gives a quantitative prediction of the experimental diffusivity. 

In this chapter we will mostly focus on the application of molecular dynamics simulation technique to understand solvation process in polymers. The organization of this chapter is as follow. In the first few sections the thermodynamics and statistical mechanics of solvation are introduced. In this regards, Flory s theory of polymer solutions has been compared with the classical solution methods for interpretation of experimental data. Very dilute solution of gases in polymers and the methods of calculation of chemical potentials, and hence calculation of Henry s law constants and sorption isotherms of gases in polymers are discussed in Section 11.6.1. The solution of polymers in solvents, solvent effect on equilibrium and dynamics of polymer-size change in solutions, and the solvation structures are described, with the main emphasis on molecular dynamics simulation method to obtain understanding of solvation of nonpolar polymers in nonpolar solvents and that of polar polymers in polar solvents, in Section 11.6.2. Finally, the dynamics of solvation with a short review of the experimental, theoretical, and simulation methods are explained in Section 11.7. 

Comparison between the experimental adsorption isotherms (adsorption pressure as a function of the amotmt of matter adsorbed) and the theoretical expression for the adsorption pressure as a function of the density of the monolayer, obtained from Steele s two-dimensional approximation, Eq (23). In this case, Henry s constant must be previously calculated from experimental data or through the gas-solid virial coefficient [210,211], Eq. (4). 

The theoretical minimum air requirement at equilibrium to strip aromatic-contaminated water can be calculated from the Henry s Law constant. Thus, at 68°F benzene stripping requires 69 SCFM of air, toluene... 

The amount of BTEX absorbed in the contactor is a function of its solubility in the glycol used, concentration in the feed gas, absorption pressure and temperature, number of theoretical trays, and glycol circulation rate. The Henry s law constant for benzene in TEG at 1,000 psia is plotted in Figure 11 37, which presents values calculated by Fitz and Hubbard (1987)... 

Kremser equation An equation used in the calculation of the number of theoretical stages required in the design of an absorption column used for absorption processes such as the drying of natural gas. It is based on the condition that the pressure divided by the product of Henry s law constant and the ratio of moles liquid to moles vapour is a constant. 

The slope of the equilibrium line is the Henry s law constant is 26 (i.e., m = 26). In this section the number of theoretical stages, the column diameter, and column height are to be calculated. 

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