Improvement of Water‐Adsorption Capacity of Silico‐Aluminophosphates by Changing Si/Al Ratio and Impregnation of Hygroscopic Salt for Application of Adsorption Chiller

We synthesized a series of silico‐aluminophosphates with a CHA‐type microporous structure (SAPO‐34) under hydrothermal conditions with different silicon to aluminum (Si/Al) ratios and systematically studied the effect of the Si/Al ratio on the structural properties and the water‐adsorption capacity of the SAPO‐34 adsorbents. The crystallinity, pore volume and surface area of the SAPO‐34 increased with an increasing the SiO 2 /Al 2 O 3 up to 1.0, and the amount of water adsorption also increased with the same trend. However, as increasing the ratio more, these properties became worse. SAPO‐34 with SiO 2 /Al 2 O 3 = 1 exhibited the highest water adsorption amount (0.359 g water /g sorbent ) at 308 K and 30% relative humidity. In order to enhance the water‐adsorption capacity further, we impregnated the SAPO‐34 with hygroscopic salts, LiCl and CaCl 2 . The amount of water adsorption at 308 K and 30% relative humidity was increased up to 0.584 and 0.664 g water /g sorbent for the LiCl@SAPO‐34 and CaCl 2 @SAPO‐34 respectively. However, after several cycles of adsorption (308 K, 12 Torr)—desorption (353 K, 42 Torr) conditions of typical adsorption chiller, the CaCl 2 @SAPO‐34 lost more than 81% of its working capacity. On the other hand, LiCl@SAPO‐34 maintained well the working capacity during five cycles. SAPO‐34 impregnated with LiCl is a highly promising water adsorbent for the application of adsorption chiller.