PHYSICAL ADSORPTION OF GASES .I. ISOTHERMS FOR MONOLAYER AND MULTILAYER ADSORPTION

Some criticisms of the Langmuir and the BET adsorption models are presented which reveal the fallacy of the Langmuir conception of physical adsorption. These errors are corrected and new isotherms for monolayer and multilayer physical adsorption derived. These isotherms are represented by the exponential functions V=V m {1-exp (-a x)} for monolayer adsorption and V=V m {1-exp (-a x)} exp (b x) for multilayer adsorption, where V is the volume adsorbed, Vm the monolayer volume, x the relative pressure of the surrounding gas phase in equilibrium with the adsorbed phase, and a and 6 two constants which describe adsorption in the first and in the second and higher layers, respectively. They are given by a=σ τ p0/√2 π m kT b=σ τ L p0/2 π m kT where σ is the area ascribed to one admolecule, τ and τ L are the average settling time of admolecules in the first and in the second and higher layers, respectively, p 0 the saturation pressure, m the mass of one molecule, and T the absolute temperature. © 1969 Dr. Dietrich Steinkopff Verlag.