AbstractThe coupled diffusion equations describing transport in a bi‐porous adsorbent (micropore‐macropore) have been solved in order to obtain the theoretical uptake curves for such a system when the adsorption equilibrium isotherm is rectangular. Solutions are presented for both the step change boundary condition generally encountered in adsorption from the gas phase and for the more complex case which is encountered in studies of adsorption from the liquid phase, when the composition of the ambient fluid changes significantly during the course of an experiment. The theoretical uptake curves are compared with the corresponding curves for a linear sys