Calorimetric investigation on zeolites, AlPO4ʹs 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.