The theoretical calculations of the mass transfer rate are based on a model which considers a nonlinear adsorption isotherms and simultaneous resistance to mass transfer in the pore adsorbent and the convective mass transfer. Numerical solutions to the diffusive-convective-controlled adsorption and desorption processes are calculated for the Langmuir and rectangular adsorption isotherms. It is shown that for the rectangular adsorption isotherm the adsorption kinetics is governed by the diffusive-convective mass transfer over a wide range of times and the desorption kinetics is irreversible process. The equations are derived to calculate from the experimental kinetics data: (a) the coefficient diffusion in the pore adsorbent, (b) the relaxation times characterizing the adsorption and desorption processes, and (c) the times needed to reach the quasiequilibrium state for the adsorption and desorption processes.