Enthalpic and Liquid-Phase Adsorption Study of Toluene-Cyclohexane and Toluene-Hexane Binary Systems on Modified Activated Carbons.

The liquid-phase adsorption of toluene in cyclohexane and hexane solutions on modified activated carbons was evaluated; the energy involved in the interaction between these solutions and the solids was determined by immersion enthalpies of pure solvents and their mixtures, and the contribution of the system constituents was calculated by differential enthalpies. The thermal treatment generated modifications that favored adsorption and interaction with the evaluated solutions, since it increased the textural parameters and the basic character of the samples. Cyclohexane could create greater competition with the adsorption sites compared to hexane, but it favored the increase in adsorption capacities (0.416 to 1.026 mmol g-1) and the interactions with the solid evaluated through the immersion enthalpies. The immersion enthalpies of pure solvents (-16.36 to -112.7 J g-1) and mixtures (-25.65 to -104.34 J g-1) had exothermic behaviors that were decreasing due to the possible displacement of solvent molecules when increasing the solute concentration in the mixtures. The differential enthalpies for toluene were negative (-18.63 to -2.14 J), mainly due to the π-π interaction with the solid, while those of the solvent-solid component tended to be positive values (-4.25 to 55.97 J) due to the displacement of the solvent molecules by those of toluene.