Evaluation of the performance of an agricultural residue-based activated carbon aiming at removal of phenylalanine from aqueous solutions

Phenylalanine removal is a necessary step for production of protein hydrolysates appropriate for consumption by phenylketonuria patients. In this study, the feasibility of employing an agricultural residue as precursor material in the production of adsorbents for phenylalanine removal from model solutions was studied. The adsorbent was prepared by treatment of the residue (defective coffee press cake) with H3PO4 and activation at 350 °C. Batch adsorption studies were conducted at 25, 35 and 45 °C. Distinct mechanisms were observed for adsorption of phenylalanine onto the prepared adsorbent depending on the solution pH. Hydrophobic interactions between carbon rings at the adsorbent surface and phenyl rings of the adsorbate molecules was deemed the predominant mechanism. Adsorption kinetics was satisfactorily described by a pseudo-second-order model and Langmuir model provided the best-fit for equilibrium description. Maximum uptake capacity of phenylananine was comparable to values encountered in the literature for synthetic adsorbents. The results show that agricultural residues present potential as materials for production of adsorbents for phenylalanine removal from aqueous solutions.

► The prepared adsorbent was microporous, with an adequate surface chemical make-up. ► The predominant adsorption mechanism was of hydrophobic type. ► Adsorption was spontaneous, homogeneous and exothermic. ► Maximum uptake capacity (65.4 mg g−1) comparable to non-residue-based adsorbents. ► Production of an agricultural residue-based adsorbent for phenylalanine removal.