Single-component and competitive adsorption of levulinic/formic acids on basic polymeric adsorbents

The adsorption equilibria of single-component and binary mixtures of levulinic/formic acids in the aqueous solution on three different types of basic polymeric adsorbents were experimentally measured at 30 °C. Adsorption isotherms such as Langmuir, Freundlich and Sips were applied to correlate the single-solute adsorption data. Results demonstrated that the adsorption isotherms of both acids on all three adsorbents were best described by the Sips model, and that formic acid has higher adsorption capacity and stronger affinity on all three resins. The adsorption of binary mixtures of formic/levulinic acids reveals that formic acid is preferentially adsorbed and levulinic acid can be competitively displaced by formic acid. Binary Sips model and the ideal adsorbed solution (IAS) theory were employed to simulate the binary competitive adsorption data. The binary Sips model cannot predict the competitive adsorption behavior. The IAS model was successfully coupled with Sips isotherm parameters determined from single-component adsorption data to predict the binary competitive adsorption behavior of levulinic/formic acids on all three resins.