RESUMO
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.
RESUMO
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 E o and micropore volume W o. 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 E o W o with the Stoeckli and Kraehenbuehl equations. Subsequently, values of E o W o 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 E o W o, was benzene, because it had a smaller molecular size and a higher dielectric constant.
RESUMO
The objective of this data article is to show by calorimetric curves and the immersion enthalpies the differences between the interactions that occur when two activated carbons of different textural and chemical properties are put in contact with C6 compounds (an aromatic and a closed chain aliphatic: benzene and cyclohexane, respectively) in their pure state, and subsequently in mixtures thereof, with different molar composition. The greatest interaction occurs with the activated carbon that has the lower content of oxygen groups on the surface, both for the pure solvents, as for the mixtures; As for wetting liquids, there is a greater interaction with benzene (-∆Him: 94.98-106.40â¯Jâ¯g-1) than with cyclohexane (-∆Him: 21.23-65.97â¯Jâ¯g-1). The immersion enthalpy values for the different molar fractions are between -36.51 and -79.69â¯Jâ¯g-1 for the oxidized sample, and between -50.43 and -85.59â¯Jâ¯g-1 for the sample without chemical modification.