Optimization of porous materials for thermochemical storage of heat

Abstract

Increasing interest in the application of the thermochemical storage or adsorption heat pumps for utilization of industrial waste heat and solar heat stimulated several experimental and theoretical studies on short and long term heat storage (Tchernev, 2001, Mittelbach et al., 2000, Hauer et al.,1999) as well as heat driven heat pumps (Meunier,, 1986, Dieng, and Wang, 2001). However, less attention was paid to the properties of the porous materials such as common zeolites, silica gels or aluminosilicates which are mainly designed for catalysis and adsorption technologies but are not optimized for thermochemical heat storage applications. In recent years some new storage materials were suggested and characterized such as the so called composite adsorbens (Levitskij et al., 1996, Janchen et al., 2000) which have considerable high storage densities, a low charging temperature but their temperature lift is limited. Very recently (Janchen, et al., 2002) we suggested the introduction of the AlPO4’s for heat storage and heat transformation purposes. AlPO4’s are zeolites-like microporous materials, which are mildly hydrophilic and may have the potential to close the gap between silica gels and zeolites in respect to the optimization of the adsorption strength of the water and the ability to be desorbed at mild conditions. Those microporous aluminophosphates can be modified by incorporation of some silicon into the lattice to tailor their adsorption properties with respect to the water adsorption/desorption properties. The aim of this paper is to characterize the state of the art of the optimization of those new thermochemical storage materials, based on recent results, as an starting point for a continuation of the this project.