The objective of this work is to propose a calculational model for the surface-diffusion based Pressure Swing Adsorption. The assumptions inherent in the model are that the PSA column behaves as a series of stirred cells and then on the application of Fick's law in each cell the transfer of sorbed species in a particle is calculated; in the depressurization period the column pressure is assumed to decrease in a step-wise manner and the intraparticle species mass transfer is evaluated for each constant pressure step. The calculational results for a benzene-activated carbon system show little desorption taking place in the depressurization stage.