On the Kinetics of Ionic Liquid Adsorption onto Activated Carbons from Aqueous Solution

Adsorption with activated carbons (ACs) has been recently proposed as a thermodynamically favored treatment to remove and/or recover ionic liquids (ILs) from aqueous streams. In this work, a kinetic analysis of the adsorption of a hydrophobic IL (1-methyl-3-octylimidazolium hexafluorophosphate, OmimPF(6)) by commercial ACs was performed. The results indicated that adsorption kinetics is remarkably slower for the IL than for phenol, used as a reference solute. Then, the effects of the main operating conditions (stirring, AC particle size, temperature, and initial concentration of IL) on the adsorption rate were investigated. For the purpose of developing criteria to improve the kinetics of IL adsorption with ACs, different empirical and phenomenological kinetic models were applied to describe the experimental adsorption data. The kinetic analysis indicated that the mechanism of IL adsorption onto ACs is mainly controlled by the mass transfer into the pores. Therefore, the selection of adequate particle size of the adsorbent plays a major role in the development of feasible IL adsorption. Increasing the temperature led to significantly faster adsorption, which was found to be of interest for removing and/or recovering IL from aqueous solution in spite of the associated decrease of equilibrium capacity.