Simulation of fixed-bed adsorption column with axial particle diameter profile for removal of solutes at low concentration

Abstract

This study developed a mathematical model of a fixed-bed adsorption process that allows variations in particle diameter axially in the bed. The mathematical model assumes that: the bed is formed by small spherical particles; the feed solution is diluted (Henry's law region of isotherm); and the external mass transfer resistance is negligible when compared to the resistance within the particle. The mass balance for solute concentration in the adsorbent particles is analytically solved and the mass balance for solute concentration in the mobile phase is numerically solved by different methods, with subsequent adoption of the Thomas algorithm to solve the formed system of equations. These analytical and numerical solutions are joined together with Duhamel’s theorem. Studies adopting a variable profile of the particle diameter along the bed demonstrated that descending profiles along the bed saturate more slowly than ascending profiles, and that the larger the fraction of the bed using larger particle diameters, the closer to ideality is the profile of the breakthrough curve, but the breakpoint time is shorter. These findings allow the improvement of a fixed-bed adsorption process in different ways by changing the particle diameter profile configuration as needed.