Correlation of aqueous-phase adsorption isotherms

A correlation was developed to estimate the adsorption equilibrium capacity of various adsorbents and organic compounds using a combination of Polanyi potential theory and linear solvation energy relationships (LSERs). Polanyi theory provided the basic mathematical form for the correlation. LSERs were used to normalize the Polanyi theory based on the fundamental interaction forces between the solvent, adsorbate, and adsorbent expected in aqueous-phase adsorption. The correlation was developed using 56 organic compounds and eight adsorbents. The following classes of organic compounds were used: (i) halogenated aliphatics, (ii) aromatics and halogenated aromatics, (iii) polyfunctional organic compounds and (iv) sulfonated aromatics. The adsorbents were (i) three coal-based activated carbons (F-300, F-400, and APA), (ii) one coconut shell based activated carbon (580-26), (iii) one unspecified activated carbon, and (iv) three synthetic polymeric adsorbents (XAD-4, XAD-7, and XEN-563). The proposed correlation, which considers the fundamental solvent-adsorbate-adsorbent interaction forces, showed a significant improvement in predicting the adsorption capacity over a correlation that considered only van der Waals forces. However, the correlations did not predict the adsorption capacities of highly soluble organic compounds such as polysulfonated aromatics and polyfunctional organic compounds.