IMPROVED HORVATH-KAWAZOE EQUATIONS INCLUDING SPHERICAL PORE MODELS FOR CALCULATING MICROPORE SIZE DISTRIBUTION

Since its publication, the Horvath-Kawazoe (H-K) equation has been rap idly and widely adopted for calculating the micropore size distributio n from a single adsorption isotherm measured at a subcritical temperat ure (e.g. N-2 at 77K or Ar at 87K). In the H-K formulation, the ideal Henry's law (linearity) is assumed for the isotherm, even though the a ctual isotherms invariably follow the typical type I behavior, which i s well represented by the Langmuir isotherm. The H-K formulation is mo dified by including the nonlinearity of the isotherm. Inclusion of non linearity results in sharpening of the pore size distribution and shif ting of its peak position to a smaller size. Furthermore, the H-K equa tion is extended to spherical pores, and the improved H-K equation for spherical pores by including isotherm nonlinearity is also given. It is shown that the spherical-pore model is particularly useful for zeol ites with cavities. Using the literature isotherm data, the improved H -K equations for three pore geometries (slit shape, cylinder and spher e) are compared with the original H-K equations. Clear improvements ar e seen in the calculated micropore size distributions by using the imp roved H-K equations.