Performance predictions for a new zeolite 13X/CaCl2 composite adsorbent for adsorption cooling systems

Composite adsorbents synthesized from zeolite 13X and CaCl2 were investigated for applications in solar adsorption cooling systems. The effects of Ca ion exchange on the adsorption properties of zeolite 13X were studied. Ca ion exchange was found to decrease the specific surface area of the zeolite while increasing the total pore volume. Soaking zeolite 13X in 46wt.% CaCl2 solution for 24h gave the optimum Ca ion exchange. The increase in the total pore volume facilitated further impregnating the zeolite with CaCl2. In all, 41.5mol% of CaCl2 was impregnated in the Ca-ion-exchanged zeolite from a 40wt.% CaCl2 solution to form the zeolite 13X/CaCl2 composite adsorbent. A 0.4g/g difference in equilibrium water uptake between 25 and 75°C at 870Pa was recorded for the composite adsorbent. This was 420% of that of zeolite 13X under the same conditions. Numerical simulation predicts that an adsorption cooling system using the composite adsorbent could be powered by a low grade thermal energy source using the temperature range 75–100°C. Greatly improved efficiency is predicted compared to a system using pure zeolite 13X or impregnated silica gel.