A calculational model is proposed for the pore-diffusion based PSA. In principle the model is identical with that of the previous work on the surface-diffusion based PSA, except for the diffusion coefficient being inversely proportional to pressure. From the calculation for a methane-activated carbon system it is found that the increase in the intraparticle diffusion coefficient in the depressurization stage increases desorption, but a considerable desorption still occurs in the purge stage. In this work we also show that the maximal discharge of sorbate mass increases when the depressurization is accomplished in a short time. The process consisted of the adsorption, depressurization and purge stages is compared with the process having only the adsorption and purge stages in terms of the discharge of sorbate mass and the volume of gas leaving the column bottom.