Modeling of the static batch desorption and dynamic column elution of geniposidic acid from a porous anion-exchanger

For several decades, plenty of iridoid glycosides including geniposide (GS) and geniposidic acid (GSA) in the gardenia yellow pigment extraction waste water was not recovered effectively. This study is aimed to supply an efficient GSA recycling route. In this study, a model incorporating a superficial desorption rate constant was applied to the batch GSA desorption process, i.e., recycling, for verification. Then, the model was further developed to research the feasibility in dynamic column elutions simulation through porous uniform media. The simulation approach was done by coupling velocity field and mass transfer equations using COMSOL Multiphysics™ Finite element method, with appropriate mesh refinement was employed to solve the equation system. The HCl solutions ranging from 0.03 mol/L to 0.06 mol/L were used to desorb/elute the GSA from a presaturated polymeric porous anionic resin D08. Good results were accomplished in terms of ion exchange desorption rate and GSA recovery. The pore diffusion model (PDM) considering counter ion was established to describe the desorption/elution kinetics in the batch/column experiment. By the least square fitting method, the superficial desorption rate constant K_d of GSA/HCl reaction on the ion-exchange sites of porous resin was fitted to 0.116 L/(mol s). Subsequently, this value was sequentially applied in the simulation of the dynamic elution process. The individual pore diffusion coefficients for GSA and Cl^- were estimated to be 5.07 × 10^-10 and 1.77 × 10^-9 m²/s, respectively. In order to validate the simulation feasibility of this pore diffusion model to a dynamic column elution process, the effects of HCl concentration, flow rate and column's height/diameter ratio on the column performance were investigated systematically. The results from this work should serve as motivation for further experimental and theoretical study in the scaling-up of GSA purification process. Finally, repeated adsorption-elution column cycles were simulated by the PDM model well.