Characterization of sorption kinetics of CO2 from N2-rich gas mixtures studied by breakthrough experiments on Zeolites

Presented at:

• AiChE Annual Meeting 2019, November 10-15, Hyatt Regency, Orlando by Dr. Andreas Möller
• EBA 13, Encontro Brasileiro sobre Adsorção, December 1st, 2020 by Dr. Andreas Möller

The removal of CO2 from CO2-containing gas mixtures is essential in many purification processes. This purification step plays a major role for cleaning of natural gas, for upgrade of bio- or synthesis gas as well as for the purification of hydrogen after a steam reforming process and removal of CO2 from air before cryogenic air separation [1,2,3]. For dry gas mixtures this purpose can be achieved by adsorption of CO2 on zeolites. Along with the knowledge of isotherms the comprehension of the kinetic behavior of such materials is of high interest for an optimal process design.
In this study we investigated the shape and steepness of breakthrough curves for CO2 from mixtures with N2 on zeolite 3A, 4A, 5A and 13X. All materials were purchased from the same supplier with same particle sizes of 1.6 mm to 2.5 mm. Superficial velocities up to 0.8 m s-1 were investigated. The breakthrough of CO2 on zeolite 3A results in a spontaneous breakthrough curve due too narrow pore size in this material and therefore by kinetic-steric exclusion of CO2. All other zeolites exhibit considerable adsorption behavior with different shapes of the breakthrough curves and some differences in the corresponding temperature profiles in the adsorber bed. Zeolites 5A and 4A have similar breakthroughs in the initial part of the curves. As we expect, one can observe the steepest breakthrough curve for the zeolite 13X material. Although the pure component isotherm of CO2 in the pressure range of 50 mbar results in a higher sorption capacity for CO2 on 5A zeolite, the initial breakthrough for CO2 on 13X starts latest. This observation can be explained by the highest sorption kinetics for 13X.
Based on triples of pure component isotherms for CO2 and N2, mixed equilibria were predicted with simple multi component approaches and compared to the experimental results. Afterwards mass- and energy balances were used to calculate breakthrough curves and to estimate Linear Driving Force constants by fitting the model on experimental breakthrough curves.
[1] S. Cavenati, C.A. Grande, A.E. Rodrigues, Energy Fuels, 20 (6), 2648–26591 (2006)
[2] A. Möller, R. Eschrich, C. Reichenbach, J. Guderian, M. Lange, J. Möllmer, Adsorption., 23 (2-3), 197-209 (2017)
[3] C.A. Grande, R. Blom, A. Möller, J. Möllmer, Chem. Eng. Sci., 89, 10-20 (2013)