Insight into mass transfer during adsorption of geniposidic acid onto a fixed-bed column by numerical simulation considering influence of operating conditions on column adsorption performance

Abstract

In this work, the adsorption rate of geniposidic acid (GSA) on a fixed-bed column packed with porous adsorbents was studied, thoroughly by a Fick pore diffusion model based on numerical simulation and 3D visualization. Adsorption breakthrough curves of GSA were studied experimentally, under various operation conditions such as feeding concentrations, flow rates and packed column aspect ratio. For ion exchange adsorption of GSA onto the adsorbent used in this paper, a maximum adsorption capacity reached 637.5 mmol·L−1 at 298.5 K. Modeling method for an adsorption packed column was based on the coupling of mass transfer equations with a steady velocity field obtained from Navier-Stokes equation. A finite element method was adopted by COMSOL Multiphysics with proper mesh refinement, to solve the equation system. Moreover, the influences of operation conditions on the magnitude and direction of mass fluxes induced by convection and diffusion were analyzed in details. 3D data of Mass fluxes proved that the existence of forming period and transferring period of mass transfer zone (MTZ), which are important knowledge for comprehending the dynamics of adsorption process. The magnitude of convection flux was almost 107–108 times larger than that of pore diffusion flux. Average pore diffusion diffusivities of GSA and Cl− were fitted to be 5.19 × 10−10 and 1.71 × 10−9 m2·s−1, while their maximal mass fluxes were 9.366 × 10−3 and 3.926 × 10−3 mol m−2·s−1 in simulations, respectively. Finally, adsorption and elution recycle experiments proved the feasibility of the novel GSA adsorption technology in the future scaling-up process.