Water sorption on silica- and zeolite-supported hygroscopic salts for cooling system applications

Silica gel and zeolite 13X were used as supports for the hygroscopic salts LiBr, MgCl2 and CaCl2. The silica- and zeolite-supported hygroscopic salts were characterized by N2 adsorption at −196 °C and X-ray diffraction. The silica support was mesoporous whereas the zeolite support was microporous. The dispersion of CaCl2 was much lower on the zeolite than on the silica support, and the microporosity of the zeolite was blocked by the salt. CaCl2 supported on silica was a superior water sorbent versus zeolite, and CaCl2 supported on zeolite was an inferior sorbent versus zeolite. Complete water desorption from silica-supported hygroscopic salts can be effectively reached at a relatively low temperature (100–110 °C), making them candidates for efficient cooling or air conditioning applications. The isosteric heat of water desorption was obtained from the isobars and was dependent on the amount of water adsorbed. Finally, the thermodynamic cooling cycle for the SCa33 (silica gel containing 33 wt.% CaCl2) – water vapour pair showed a coefficient of performance of 0.83.