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.