Improved recovery of carboxylic acids using sequential cationic-anionic adsorption steps: A highly competitive ion-equilibrium model

A strong cationic resin (Lewatit-S2568H) was used to pre-treat four actual broths rich in carboxylic acids (CAs) to obtain free Na+ streams (final pH 1.5–2.4). Thereafter, three weak anionic resins (AnRes) were compared for the recovery of CAs by performing multicomponent batch adsorption tests using one of the pre-treated broths. Subsequently, further multicomponent adsorption tests were performed using the other three broths and the most performant AnRes (Lewatit-A365). This allowed to define adsorption isotherm profiles of CAs, Cl−, phosphates and other organic compounds (CODOther) for each broth. Besides confirming anions competition for resin exchange sites, results also evidenced that Na+ competed with the AnRes exchange sites for binding the CAs, while CODOther exerted a negligible competition for CA adsorption. A homogeneous mass action ideal model, that also considers Na+ competition, was calibrated using the collected data. It shows a very good capability to predict adsorption isotherms despite very dissimilar broths were used.