Adsorption behaviour of lactic acid on granular activated carbon and anionic resins: Thermodynamics, isotherms and kinetic studies

Solid-liquid extraction (adsorption or ion exchange) is a promising approach for the in situ separation of organic acids from fermentation broths. In this study, a diluted concentration of lactic acid (<10 g/L) separation from a model fermentation broth by granular activated carbon (GAC) as well as weak (Reillex® 425 or RLX425) and strong (Amberlite® IRA-400 or AMB400) base anion exchange resins under various operating conditions was experimentally investigated. Thermodynamic analysis showed that the best lactic acid adsorption performances were obtained at a pH below the pKa value of lactic acid (i.e., 3.86) for GAC and RLX425 by physical adsorption mechanism and above the pKa value for the AMB400 resin by an ion exchange mechanism, respectively. The adsorption capacity for GAC (38.2 mg/g) was the highest, followed by AMB400 (31.2 mg/g) and RLX425 (17.2 mg/g). As per the thermodynamic analysis, the lactic acid adsorbed onto GAC and RLX425 through a physical adsorption mechanism, whereas the lactic acid adsorbed onto AMB400 with an ion exchange mechanism. The Langmuir adsorption isotherm model (R2 > 0.96) and the pseudo-second order kinetic model (R2 ∼ 1) fitted better to the experimental data than the other models tested. Postulating the conditions for the real fermentation broth (pH: 5.0-6.5 and temperature: 30-80°C), the resin AMB400 represents an ideal candidate for the extraction of lactic acid during fermentation.