where D is the crystal or micropore

where D is the crystal or micropore diffusivity and r is the crystal radius. The adsorption equilibrium law gives the boundary condition in the crystal limit. In this work, we used the linear isotherm to describe adsorption equilibrium because the hydrocarbon partial pressures were very low and no difference was observed between introducing the Toth model or the linear model, except that with the linear model, the computation time was much faster.