Comparison of the Adsorption Dynamics of Air on Zeolite 5A and Carbon Molecular Sieve Beds

摘要

Adsorption and desorption in zeolite 5A and CMS beds were compared by using a ternary mixture (N_2/ O_2/Ar; 78 : 21 : 1 vol%). Because the breakthrough curves for both beds show a tail by temperature variance, a non-isothermal mathematical model was applied to the simulation of adsorption dynamics. The LDF model with a constant rate parameter was enough to predict the experimental breakthrough and temperature curves of an equilibrium separation bed, while the modified LDF model with a concentration-dependent parameter should be applied to a kinetic separation bed. In the CMS bed initially saturated with He, Ar was the first breakthrough component with N_2 following after a short interval. Then, after a long interval, the breakthrough of O_2 occurred with a broad roll-up due to its fast diffusion rate and the relatively slow diffusion rate of N_2. In the CMS bed initially saturated with O_2, the breakthrough curves of O_2 and N_2 showed a very broad shape because of the slow diffusion of N_2 into CMS, In the zeolite 5A bed, the breakthrough time sequence was Ar, O_2, and N_2 at very close time intervals. After the sharp roll-ups of O_2 and Ar, the variation of the breakthrough curves was negligible. The inflection of the temperature profile in the zeolite 5A bed was caused by the crossover of the O_2 and N_2 MTZs, while in the CMS bed it was caused by the difference in the diffusion rates of O_2 and N_2.