Transient rates of gas sorption. II. Rate equations for transport and adsorption in porous adsorbents

Equations are derived to describe the rate at which gas passes into a bed of adsorbent under conditions of constant volume and diminishing pressure. Of the processes which may be responsible for the observed rate of gas uptake, the following three are considered : (i) Knudsen flow within the bed, or within the granules of which it is composed, with simultaneous adsorption that is too fast to be a limiting factor ; (ii) chemisorption which is controlled by the rate of Knudsen flow ; (iii) unrestricted chemisorption.It is shown how the rate constants used in the equations are related to the overall reaction rate constant in a catalyst pore.