Temperature independent description of water adsorption on zeotypes showing a type V adsorption isotherm

Abstract

New adsorbents like aluminumphosphates (AlPO's) and siliconaluminumphosphates (SAPO's) show high potential for adsorption based heat transformation processes. These adsorbents show IUPAC type V adsorption behavior with the adsorptive water. To model heat transformation processes it is important to describe the adsorption equilibrium independent of temperature. Many groups in this research field use the potential theory by Polányi to model the adsorption process. However, the classical potential theory is not suited to describe type V adsorption behavior. This work presents an adaption of the potential theory, which enables the temperature independent modeling of the adsorption of water on zeotypes showing a type V adsorption characteristic. The adaption is based on a corrected adsorption enthalpy and consequently on a more valid description of the desorption pressure. The adaption could be verified through our own experiments on AlPO-18, SAPO-18 and TAPSO-34 adsorbents, as well as with isotherms for AlPO-5 from literature, measured at different temperatures using water as adsorptive. The results show that the presented adaption is able to describe the adsorption equilibrium independent of temperature and therefore enables modeling of adsorption based heat transformation processes with the potential theory of adsorption.