Adsorption kinetics and thermodynamics of theanine onto anion exchange resins

To separate the synthesized theanine by enzymatic method, the adsorption of theanine onto anion exchange resins under alkaline condition was investigated. The results revealed that the adsorption properties of strongly basic resins were better than that of weakly basic resins. While the gel-type basic resin of HZ202 was used, its equilibrium adsorption capacity for theanine was 96.3 mg/g at pH 9.0. The experimental results showed that theanine was loaded on the HZ202 resin with a non-uniform distribution. The isotherm data well fit to Sips model. The ΔG change was all negative at different temperatures, indicating that the adsorption process was exothermic and spontaneous. Enthalpy change lied between 20.9~418.4 kJ/mol, suggesting that the adsorption process was chemical adsorption. The kinetic data of adsorption fit well to the pseudo-second-order model. It suggested that the adsorption rate was limited by chemical reaction. The adsorption rate would be improved with increasing of initial concentration of theanine.