Thermodynamics of adsorption from solution. The systems (benzene + ethanol)/Graphon and (n-heptane + ethanol)/Graphon

Abstract

Measurements have been made of the adsorption by graphitised carbon black (Graphon) from liquid mixtures of benzene + ethanol and n-heptane + ethanol over the temperature range 283 to 333 K. The data have been subjected to thermodynamic analysis to obtain the standard differences between the surface excess properties of the solid/pure component interfaces, and between the enthalpies of immersion of the solid in the pure liquids. When taken with previously reported data for the system (benzene + n-heptane)/Graphon, these results demonstrate the thermodynamic consistency of the measurements of adsorption from the three pairs of binary mixtures derived from benzene, n-heptane and ethanol. The enthalpy data agree with direct calorimetric measurements. The adsorption data are also used to test the validity of the monolayer model of adsorption: this is compatible with the data for (benzene + n-heptane)/Graphon, but a minimum thickness of three layers for (benzene + ethanol)/Graphon and four layers for (n-heptane + ethanol)/Graphon is required to achieve thermodynamic consistency between a surface-phase model and the experimental data. Surface activity coefficients are calculated and show that deviations from ideality in the surface phase are roughly comparable with those in the bulk solutions.