The mass transfer mechanisms and rates of CO2 and N-2 in 13X zeolite beads were determined using volumetric frequency response (VFR) methods. The VFR experiments were conducted with each gas over a wide range of frequencies from 7 X 10(-5) to 9.5 Hz at 100, 200, and 750 Ton at 25 degrees C for CO2 and at 200, 400, and 750 Torr at 25 degrees C and at 40 and 55 degrees C at 400 Torr for N-2. The resulting experimental intensity response curves were fitted to four different non-isothermal mass transfer models, including micropore diffusion, macropore gas diffusion, macropore viscous (Poiseuille) flow, and macropore surface diffusion. The resulting experimental phase lag response curves were predicted from the resulting model parameters. The macropore gas diffusion model fitted and predicted the experimental response curves the best for both gases, confirming the mass transport of both CO(2)( )and N-2 in 13X zeolite beads is macropore gas diffusion controlled. The corresponding diffusional time constant D-p/R-p(2) values were 3.32 s(-1) for CO2 and 5.1 s(-1) for N-2.