2-STEP ADSORPTION MODELS IN MOLECULAR-SIEVES

Starting from analysis of the behaviour of peak retention time vs. the adsorption constant and vs. the mass transfer coefficient, we propose a simple macroscopic model describing adsorption in molecular sieves at high Peclet numbers and at low temperatures. The model is based on the hypothesis that adsorption kinetics evolve through the superposition of an instantaneous adsorption step and a slower step controlled by mass transfer resistance. A detailed moment analysis is performed by comparing the results of the two-step model with those deriving from classical adsorption models (linear driving force model and macropore-micropore model) and with experimental chromatographic data of H-2-D-2 adsorption on NaCa-Mordenite. The experimental results at low temperatures validate the proposed model.