Enthalpy of immersion of activated carbon in aliphatic and aromatic organic solvents: benzene, toluene, cyclohexane, hexane, and in binary mixtures of these compounds

The immersion enthalpy of activated carbons (with different surface characteristics) into benzene, toluene, cyclohexane, and hexane was evaluated. Those activated carbons were obtained from a granular activated carbon prepared from coconut shell (CAG), and the latter was subjected to oxidation processes with a HNO₃ solution and heat treatment at different temperatures (723 K, 1023 K, and 1173 K). The values for the immersion enthalpies are of exothermic nature, and their values are in a range between − 16.36 and − 145.1 Jg⁻¹. The five samples were also immersed in binary mixtures of benzene–cyclohexane (B/CH: benzene solute, cyclohexane solvent), benzene–hexane (B/H: benzene solute, hexane solvent), toluene–cyclohexane (T/CH: toluene solute, cyclohexane solvent), toluene–hexane (T/H: toluene solute, hexane solvent), and cyclohexane–hexane (CH/H: cyclohexane solute, hexane solvent) at different mole fraction concentrations between 0. 2 and 0.8, in order to show the effect of the solute–solvent–solid interaction as the solute concentration increases. The results obtained show values for the immersion enthalpy between − 145.2 and − 9.62 Jg⁻¹. The immersion of porous solids into the pure solvents indicated that the interaction with aromatic compounds released greater energy than the interaction with aliphatic compounds. On the other hand, the immersion into the solvent mixtures showed higher immersion enthalpy values for the porous materials subjected to thermal treatment, and this pointed out that this treatment generated the removal of oxygenated groups, increasing the basic character of the samples related to the presence of delocalized π electrons that interacted mainly with the aromatic compounds; therefore, the immersion enthalpy values were much higher.