An analysis of gas chromatography pulse dispersion data for the system n-butanelzeolite NaY is presented. The data were analyzed in terms of two models, an intracrystalline diffusion limiting model and a surface barrier model. Both models provided acceptable fits to the pulse dispersion data; however, the temperature dependence of the apparent mass transport parameters strongly suggests that a surface barrier is responsible for the observed transport resistance. The Henry's law constants were independent of choice of model and the isosteric heat of sorption was consistent with literature values. Chen-Chen SCOPEThere are indications in the literature that diffusion measurements in zeolites by the sorption rate technique may under certain circumstances be controlled by a surface barrier resistance. This is most likely to occur for rapid diffusion in small crystals of large-pore zeolites. However, another phenomenon must be considered in analyzing such systems, namely the sorption heat effect. Failure to take into account either the surface barrier or the sorption heat effect will result in erroneously low reported values of intracrystalline diffusivity. It is important to distinguish between these effects because of the many applications of large-pore zeolites in industry.Pulse gas chromatography offers a potential means for eliminating the sorption heat effect, and at the same time it should be sensitive to a surface barrier. In the present study we have undertaken a study of n-butane sorption and diffusion on a commercial sample of zeolite Nay. The data are analyzed on the basis of an intracrystalline diffusion model and a surface barrier model. We earlier reported results on the n-butanelNaY system, but it was not possible to obtain quantitative results due to a system nonlinearity (Hsu and Haynes, 1981). This problem was eliminated in the present study by using much more sensitive detectors. CONCLUSIONS AND SIGNIFICANCEBy injecting highly diluted n-butane pulses into our system it was possible to operate in a linear region where complications from nonlinear sorption, non-fickian diffusion and sorption heat effects were absent. Henry's law constants were independent of the choice of model, and the isoteric heat of sorption compared favorably with literature values on a similar zeolite (NaX). It was not possible t o distinguish between anCorrespandencz concerning this paper should be addressed to H. W. Haynca. Jr. 1848November 1986 intracrystalline diffusion model and a surface barrier model on the basis of goodness of fit. However, arguments based on the apparent activation energies support the surface barrier model. Furthermore, it appears that the surface barrier is due to a finite rate of adsorption from the gas phase, as opposed to pore constrictions just under the zeolite crystal surface. This interpretation leads to the conclusion that the sticking coefficient for molecules colliding with the external surface is of the order of lo-'. Such a small value of the Vol. 32, No. 11 AICbE Journal sticking coeff...