Calculation of Adsorption Energy Distributions of Silica Samples Using Nonlinear Chromatography

Abstract

The estimation of adsorption energy distributions from nonlinear chromatographic data is considered in detail from both experimental and theoretical viewpoints. The experimental data is obtained on DAVISIL, IMPAQ, and VYDAC silica samples. The adsorbates studied include diethyl ether, methanol, ethanol, tetrahydrofuran, pyridine, and heptane. The theoretical models of adsorption studied are the Langmuir, Jovanovic, Fowler-Guggenheim (both random and patchwise), and Brunnauer-Emmett-Teller local isotherms. The chromatographic data is obtained with the use of high-efficiency porous layer open tubular columns. The experimental variables of temperature and maximum solute partial pressure are studied for their effect on the data and estimation. The validity of the technique is assessed. It is concluded that adsorption energy distributions may only be calculated accurately and without bias for systems in which the majority of the adsorption energy is 10 kJ/mol greater than the heat of vaporization of the solute. For adsorption energies less than this, intermolecular interactions decrease the accuracy and confidence of the results. Other experimental parameters also limit the scope of studies of this kind. 14 refs., 12 figs., 2 tabs.