Experimental Investigation on Adsorption and Surface Characteristics of Salt Hydrates and HydrophobicPorous Matrix Based Composites

Asnakech Lass-Seyoum1, D. Borozdenko1, T. Friedrich1, K. Schönfeld2, J. Adler2, and S. Mack3

1. ZeoSysGmbH, Falkenberger Straße 40, 13088 Berlin, Germany

2. Fraunhofer Institute for Ceramic Technologies and Systems IKTS, Winterbergstrasse 28, 01277 Dresden, Germany

3. Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, Nobelstraße 12,70569 Stuttgart, Germany

Abstract: In the studies reported here more than nine different hygroscopic active salt hydrates and two groups of mesoporous hydrophobic substrates have been used to prepare a wide range of composites for closed sorption thermochemical storage application. The first group of substrate material that has been employed to incorporate the salt hydrates is consisted of both pure and in various form modified attapulgite, whereas the second group involved different kinds of activated carbons. The composites reported here were prepared by direct incorporation of the substrate with a pre-defined concentration of salt hydrate solution. Composites based on porosing agent modified attapulgite and those calcined at a temperature of 400°C present poor thermal stability and unfavorable dynamic performance associated with pressure drop across the bulk material resulting in 15-20% decrease on adsorption capacity. Following a pre-selection of an appropriate material out of a wide range of composites, short and long term cyclic tests were performed. Among all the investigated materials in this work, both pure attapulgite calcined at 550°C (Att550) and Poolkohl (PK) based composites containing CaCl2, MgCl2 and LiCl exhibit an optimum adsorption and surface behavior including high thermal stabilities under hydrothermal conditions over 250 cycles.

Key words: salt hydrates, composites, hydrophobic, thermo-chemical, dynamic adsorption