Two-Dimensional Transport Dispersive Model for Separating Glycolic Acid and NaCl with Ligand Exchange Chromatography

A two-dimensional transport dispersive (TD) model, based on the Navier-Stokes equation, describing an energy conservation of fluid motion, and a one-dimensional TD model, were built to describe the diffusions of glycolic acid (GA) and NaCl in the axial and radial directions in a preparative column. The elution and breakthrough curves of GA and NaCl were simulated with the models, and the instantaneous concentrations of GA and NaCl in the column were further studied. The results indicated that the two-dimensional TD model simulated the elution curve of GA, whereas that of NaCl could be simulated with the one- or two-dimensional TD models. The parameters of the models were obtained by combining the empirical and inverse methods, which enhanced the simulation accuracy. The external transfer diffusion was the rate-controlling step during adsorption of GA due to a Biot constant less than 10. Moreover, the concentration of NaCl was slightly higher than that of GA at the same axial position in the column, and the diffusion fronts of GA and NaCl were in a parabolic form. On increasing the column temperature, the retention time of GA and the resolution gradually decreased, whereas the diffusion of NaCl did not change appreciably. The breakthrough volumes of both NaCl and GA remained unchanged, and the total transfer coefficient of GA showed a downward trend overall within the experimental range.

Automated summary

A two-dimensional transport dispersive model based on the Navier-Stokes equation and a one-dimensional transport dispersive model were built to describe the diffusions of glycolic acid (GA) and NaCl in a preparative column. The models successfully simulated the elution and breakthrough curves of GA and NaCl, and the concentration profiles in the column. The results indicated that the external transfer diffusion was the rate-controlling step for GA adsorption, and the concentration of NaCl was slightly higher than that of GA. Increasing the column temperature led to a decrease in the retention time of GA and its resolution, while the diffusion of NaCl remained relatively unchanged.