Interaction between Hydrocarbons C6 and Modified Activated Carbons: Correlation between Adsorption Isotherms and Immersion Enthalpies.

Abstract

Adsorption isotherms of benzene, cyclohexane, and hexane were determined from the gas phase on microporous activated carbons with Brunauer–Emmett–Teller areas between 816 and 996 m2 g–1. The Dubinin–Radushkevich equation was used to calculate the parameters of characteristic energy Eo and micropore volume Wo. Also, immersion enthalpies of activated carbons in solvents were obtained (benzene: −95.0 to −145.1 J g–1; cyclohexane: −21.2 to −91.7 J g–1; and hexane: −16.4 to −66.1 J g–1), and they were used to calculate the product EoWo with the Stoeckli and Kraehenbuehl equations. Subsequently, values of EoWo from the two techniques (between 512 and 2223 J cm3 mol–1 g–1 for the adsorption isotherms; between 1204 and 12008 J cm3 mol–1 g–1 for immersion enthalpies) were correlated with some characteristics of the adsorbate such as molecular size, the molar volume, and the dielectric constant. It was found that modifying the activated carbon affected the adsorption process, being favored by temperature changes and restricted by oxidation processes. The adsorbate, which showed the highest values for EoWo, was benzene, because it had a smaller molecular size and a higher dielectric constant.