MICROCALORIMETRIC AND ANALYTIC DETECTION OF SOLID-GAS INTERACTION ON POROUS ADSORBENTS

Adsorption of CO2 gas on two adsorbents with different surface energie s, i.e., silica gel and activated carbon was studied at various temper atures. Isosteric adsorption heats were calculated from the isotherms. Adsorption enthalpies were measured directly by gas microcalorimetry at 298 K as a function of equilibrium pressure and, consequently, the amount of material adsorbed. It was established that in the case of ac tivated carbon, an apolar adsorbent, differential adsorption enthalpy' calculated from isosteric adsorption heat is in good agreement with t he values determined by gas microcalorimetry. A significant difference was observed, however, in the case of the polar silica gel where spec ific interactions may be expected to arise between the surface and CO2 molecules. The thermodynamically consistent Toth equation [8] has bee n applied to the measured isotherms and the parameters of that also in dicate the specific interactions mentioned above.