Adsorption from binary solutions of polar n-decyl derivatives and heptane onto alumina

The preferential adsorption of n-decanol, n-decylamine, n-decanoic acid, and ethyl octanoate from binary solutions with heptane onto alumina was studied. The net surface excess isotherms were measured and resolved into component isotherms. The heat of immersion of the alumina in n-decanol, ethyl octanoate, and n-decanoic acid solutions was measured. The heats of immersion support the resolved isotherms which indicate that the order of preferential adsorption is n-decanoic acid > n-decanol ≃ n-decylamine ≃ ethyl octanoate. However, adsorption equilibrium constants calculated for each system indicate that the order of preferential adsorption is ethyl octanoate > n-decanol > n-decylamine > n-decanoic acid. An explanation for the discrepancy is put forth. A theoretical model of surface heterogeneity is also applied to the data for the ethyl octanoate and n-decanol systems. The reasonable fit of the model in each case suggests that the alumina surface is heterogeneous.