Adsorption kinetics, isotherms and thermodynamics of aromatic amino acids in feather hydrolysate onto modified activated carbon

The main objective of this study was to produce low cost activated carbons for the adsorption of aromatic amino acids (AA) from feather hydrolysate. By optimizing the static adsorption conditions (time, pH and concentration) of amino acids, the adsorption amounts of tyrosine and phenylalanine reached 15.2 and 20.1 mg/g, respectively, under optimal conditions. Furthermore, it exhibits excellent reusability as it maintains a removal efficiency of 82.0% and 82.8% for tyrosine and phenylalanine after being reused 4 times. The effects of NaOH modified activated carbon (NA-AC) on the adsorption capacity of AA in feather hydrolysate at different temperatures (298.15, 308.15, 318.15 K) were investigated, and the static adsorption kinetics curves were plotted. The adsorption isotherm (Langmuir, Freundlich model), kinetics (pseudo-first-order-mode, pseudo-second-order-mode, particle diffusion model) and thermodynamics were studied. The results shown that the adsorption process of AA onto NA-AC accorded with the pseudo-second-order-mode. The adsorption rate was mainly controlled by the liquid film diffusion and the particle diffusion. The adsorption isotherm accorded with the Langmuir adsorption isothermal model. Adsorption was an endothermic process, and increasing temperature was conducive to adsorption. Gibbs energy & UDelta;G indicated that the adsorption process was spontaneous, and enthalpy oH indicated that the adsorption process was mainly physical adsorption. The proposed adsorption mechanisms provide a theoretical basis for the optimization of AA separation and purification process in feather hydrolysate by NA-AC, which may further improve the separation and purification efficiency of other amino acids in feather hydrolysate.