Modeling of fixed-bed columns for gas physical adsorption

Abstract

Adsorption processes may be classified as purification or bulk separation, depending on the feed concentration of the compounds to be adsorbed (adsorbates). The adsorption dynamics of a fixed-bed is crucial for a well-designed adsorption process. This work focuses on physical adsorption and provides a modeling to predict the breakthrough curves using a minimum set of experimental data. The modeling does not require one to obtain key parameters from the experiment unlike other modeling found in the literature. In addition, boundary conditions, thermal effects, correlations to be used, and the homogeneous/heterogeneous modelings are discussed for 1-D modeling, after verifying that it provides the same output as 2-D modeling does. Moreover, it is demonstrated that pseudo-homogeneous modeling is realistic, so a more complex heterogeneous modeling is not necessary. The modeling has been tested against five sets of experimental data: three cases of bulk separation and two cases for purification. The simulation was carried out by Comsol Multiphysics software, and a good match between the experimental data and the simulation output was achieved, which demonstrates the applicability of the modeling, so it may be used with confidence. Purification can be modeled as an isothermal process, and no energy balance equation is needed. However, for bulk separation, noticeable thermal effects may take place due to the relatively high adsorbed gas that consequently releases a higher amount of heat; at the same time, the superficial fluid velocity is reduced due to the decrease in the flow-rate, and the gas properties change, affecting the breakthrough curves.