Recovery of Citric Acid from Fermentation Broth Using Supported Ionic Liquids

Citric acid is widely used in the pharmaceutical, food, and cosmetic industries. However, the recovery of bioproduced citric acid from fermentation broths typically involves purification steps that generate substantial waste. This work proposes an alternative recovery strategy based on the selective adsorption of citric acid using supported ionic liquids (SILs). Two SILs were prepared by immobilizing the IL ligands diethylpropylethanolammonium chloride ([Si]-[N_3222OH]-Cl) and 1-propyl-3-methylimidazolium chloride ([Si]-[C₃C₁Im]-Cl) onto a solid silica support. The materials were characterized by ¹³C NMR spectroscopy, elemental analysis, and determination of the specific surface area (S _BET). Batch adsorption experiments were conducted to evaluate the effects of contact time, initial citric acid concentration, temperature, and pH. Adsorption kinetics were analyzed using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Boyd models, while equilibrium data were interpreted using the Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. The pseudo-second-order model best described the adsorption kinetics, whereas the Freundlich model provided the best fit for the equilibrium data. Maximum adsorption capacities of 577 and 793 mg·g^-1 were obtained for [Si]-[N_3222OH]Cl and [Si]-[C₃C₁Im]-Cl, respectively. Reusability of the SILs was also assessed through successive adsorption-desorption cycles. The SILs enabled a citric acid desorption range of 43.8% to 100%. Finally, the materials were applied to the recovery of citric acid directly from a fermentation broth to evaluate their potential for industrial application. Overall, these results highlight the potential of SILs as promising adsorbent materials for the efficient recovery of citric acid from fermentation broths, paving the way for their widespread use at the industrial scale.