EVALUATION OF THE ENERGY-DISTRIBUTION FUNCTION FROM LIQUID-SOLID ADSORPTION MEASUREMENTS

Various problems associated with numerical evaluation of the adsorption energy distribution function, F(U21), from the experimental excess adsorption isotherms of binary nonelectrolytic liquid mixtures on heterogenous solid surfaces have been discussed. Several methods known in the literature did not address the numerical ill-posed character of the integral equation, which has been used for calculating F(U21). In the current work two alternative approaches, which take into account the ill-posed nature of this integral equation, have been presented. In the first approach a regularization method has been employed, whereas in the second one an expansion of the Stieltjes' transformation has been utilized. Also, the problem of choice of the local adsorption model has been considered. A representation of the overall excess adsorption isotherm in the form of the M(t)-plot has been found to be useful for selecting this model. Illustrative calculations have been carried out for various mixtures on the same adsorbent and for one mixture on different adsorbents. Such as methodological approach is especially useful for analyzing differences between the systems studied. By use of the regularization method, the distribution functions F(U21) for n-hexane/1-hexanol, n-hexane/toluene, and n-hexanol/toluene on an active carbon have been calculated and compared. Another comparison of the F(U21) functions have been presented for water/ethanol on ZSM-5 zeolites of different Si/Al ratios.