The Separation of amino acid by displacement chromatography in a media of Dowex 50W-X8 cation exchange resin in $H^+$ form was investigated.
Equilibria data for the adsorption of amino acids were determined. Adsorption isotherms for Glutamic acid and Alanine were measured in the concentration range up to 100mmol at 30℃. Langmuir and Langmuir-Freundlich isotherms were tested with the experimental data. To estimate the adsorption behavior of the mixture of amino acid, we assumed that the parameter in multicomponent isotherm is equal to that of single component isotherm and the parameter of hydrogen is 1. Also we introduced new variable ion fraction to predict adsorption equilibria indifferent to the initial HCl concentration. And then Langmuir-Freundlich isotherm estimate the adsorption characteristics very well.
Because the overall mass transfer is independent with concentration, the kinetic parameters of the system were determined from the chromatographic measurement at the range of linear adsorption equilibrium by the moment method.
A theoretical model including the mass transfer resistance with nonlinear isotherm was used to evaluate the column performance. The orthogonal collocation method with two interior collocation points was adapted to finite element with six elements to solve the model equation. The solution of the model equation provided a pairly well prediction of the experimental chromatography data.
Various operating conditions such as the eluent flow rate, pH, displacer concentration were tested to find the optimal condition on the separation. The displacer was NaOH or HCl solution. According to the experimental results, as the flow rate and displacer concentration increase, operating time and the concentration of the products improve but the resolution is decreased. When HCl solution was used as a displacer instead of the NaOH solution, chromatography peaks appeared fast but with the tailing.
