Systematische Untersuchung des Einflusses von Aluminiumdichte und Struktureigenschaften auf das Wassersorptionsverhalten von Zeolithen

• Systematic investigation of the influence of Aluminum density and structural properties on the behavior of zeolites in water sorption

Maaz, Swaantje; Palkovits, Regina (Thesis advisor); Rose, Marcus (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

Thermally operated heat pumps may play an important role in the usage of waste heat. Their efficiency can be influenced among other things by modifying the structural and chemical properties of the adsorbent. The focus of this thesis is the influence of Aluminum density and other structural properties, e.g. specific surface area, pore volume and proportion of micro-/mesopores, on the behavior of zeolites in water vapor sorption. A holistic approach is necessary to put the correlations in perspective, to be able to establish a structure-property-correlation and to use that knowledge to tailor adsorbents for any application. Commercially available zeolites of different framework types were thoroughly analyzed using nitrogen physisorption and water physisorption. The influence of the counterion in the framework was discussed in a type FAU zeolite (Li+, Na+, NH4+, H+). Furthermore, several hierarchical zeolites of type LTA and MFI were used to investigate the influence of meso- and macropores on the water sorption behavior. The water sorption isotherms were also qualitatively evaluated concerning the course of the isotherm. In addition, the pore filling degree at low and high relative pressure was calculated which showed a deviating water sorption behavior for different framework types with the same Aluminum density. Across all investigated areas the influence of the structural properties was significant. All in all, it was obvious that the adsorption of water on zeolite is complex and highly influenced by the material properties. Hence, a simple consideration of the sorption capacity (loading at high relative pressure), as often seen in literature, is not enough to determine the qualification of a zeolite as an adsorbent in an adsorption heat pump.