(338j) Adsorption of Cationic Surfactants Onto Nonionic Polymeric Adsorbents - Influence of Micelle Formation
Hydrophobic polymeric adsorbents offer two advantages in adsorptive removal of surfactants from water: high adsorption capacity and a possibility to regenerate the adsorbent by using an aqueous ethanol solution.
In this work, adsorption of cationic surfactants (C12 and C14 homologues of benzalkonium chloride) onto polymeric resins XAD-7 and XAD-16 was investigated in a batch adsorber. The influence of adsorbate concentration, temperature and ionic strength of the liquid phase on adsorption equilibrium was studied. In particular, the influence of micelle formation in the liquid phase at concentrations higher than the critical micelle concentration was of interest.
It was found that adsorption depends strongly on the hydrophobisity of the surfactants and the polymers. Highest affinity was found between styrenic XAD-16 polymer and the C14 homologue. Adsorbed amounts were found to decrease with increasing temperature as expected. The adsorption enthalpy and entropy were calculated from the temperature dependence of the adsorption equilibrium constant at infinite dilution. Increased adsorption with increasing ionic strength could stem either from ?salting out? or from decreasing range of electrostatic interaction between the adsorbates. Micelle formation was found to have a strong influence on the adsorbed amounts. The experimental data were successfully correlated with adsorption models assuming multilayer adsorption and micelle formation in the liquid phase.