Interactions during the Adsorption of Heterocycles on Zeolites, Silica Gels, and Activated Carbons

The adsorption of the heterocycles cyclopentane, tetrahydrothiophene, tetrahydrofuran, and pyrrolidine on five adsorbents (one zeolite, two activated carbons, and two silica-alumina gels) was studied with a sensor gas calorimeter at 25 degrees C. Systematic data on simultaneously measured adsorption isotherms and load-dependent heats of adsorption are given. The adsorption isotherms show that the maximum loading is arranged according to the molar volume of the adsorptives. Having the lowest molar volume, tetrahydrofuran reaches the highest saturation loading on all adsorbents. Based on the measured data, the prevailing interactions and their strength are analyzed. Depending on the functionalities, dispersion, induction, and dipole interactions as well as hydrogen bonds can be formed between the adsorptives and the adsorbents' surfaces. Since pyrrolidine can act as a donor and an acceptor in hydrogen bonding, it achieves the highest heat of adsorption in all measurements. As pyrrolidine shows a stepwise decrease in the heat of adsorption on the silica-alumina gels, it represents a promising sample molecule for an accurate energetic characterization of silica-alumina gels.