FREQUENCY-RESPONSE FOR NONISOTHERMAL ADSORPTION IN BIPOROUS PELLETS

The frequency response for nonisothermal adsorption in a biporous pell et is analyzed theoretically, using a mathematical model which include s heat and mass transfer resistances in both micropores and macropores . It is confirmed that, when the heat effect is involved, the out-of-p hase component may exhibit a bimodal form. Moreover, it is shown that when both macropore diffusion and micropore diffusion resistances are comparable, macropore diffusion behaves like a surface barrier and lea ds to an intersection of the in-phase and out-of-phase response functi ons. When either micropore diffusion or macropore diffusion alone is d ominant, the frequency response is essentially the same and, therefore , provides no information concerning the nature of the controlling dif fusional resistance. Experimental data for light linear paraffins-5A, reported by Yasuda et al. (1991, J. phys. Chem. 95, 2486-2492), are re analyzed by the present nonisothermal model. It turns out that the rep orted experimental response can be equally well represented by a nonis othermal model using several different combinations of mass transfer r esistances. It, therefore, appears that the bimodal behavior of the ex perimental out-of-phase data is caused by the heat effect, thus contra dicting the conclusion of Yasuda that there are two adspecies with dif ferent mobilities. With the reported data, it is, however, not possibl e to extract reliable values for the intracrystalline diffusion coeffi cient, and the nature of the controlling mass transfer resistances can not be established with certainty.