Calorimetric investigation on zeolites, AlPO4's and CaCl2 impregnated attapulgite for thermochemical storage of heat

The sorption properties of water in potential thermochemical storage materials such as low silica X zeolites, microporous aluminophosphates, SAPO-34 and CaCl2 accommodated in the pores of attapulgite were investigated by thermogravimetry, differential scanning calorimetry, sorption isotherms and microcalorimetry. Because of decreasing differential molar heats of sorption from LiLSX (100-70 kJ/mol) to SAPO-34 (90-65 kJ/mol) and to supported CaCl2 (70-50 kJ/mol) the isotherms are shifted towards higher equilibrium pressure by about three orders of magnitude. The energy densities at 313 K and up to 20 mbar vapor pressure decrease in the same order from 1184 to 997 and 871 kJ/kg adsorbens. The average temperatures for the desorption of the water decreases as well from >450 to <400 K which classifies the silicoaluminophosphate between the common zeolites and the salt hydrates with regard to the properties as thermochemical storage material. (C) 2005 Elsevier B.V. All rights reserved.