Heat Release Kinetics upon Water Vapor Sorption Using Cation-Exchanged Zeolites and Prussian Blue Analogues as Adsorbents: Application to Short-Term Low-Temperature Thermochemical Storage of Energy

Abstract

In view of potential uses in short-term thermochemical heat storage by sorption of water vapor, the capacity to release a sufficient heat amount at the appropriate rate of a Prussian blue analogue (PBA) containing hexacyanocobaltate vacancies has been compared with those of 13X type zeolites possessing Na+, Ce3+, Ce4+, or Tb3+ extra-framework compensating cations. The extended structural and surface characterization demonstrated good reproducibility of the preparation procedures performed on a 10-g scale. The adsorbents were tested under dynamic conditions of gas flow with the aid of either a gas flow calorimeter (120 mL h−1 helium flow) to measure the amount and rate of the integral heat release or a laboratory-scale test rig (15,000 to 22,800 mL h−1 nitrogen flow) to monitor the outlet temperature of nitrogen heated by adsorption. For a regeneration temperature of 353 K and a partial H2O pressure of 2.8 kPa in helium, the PBA sample yielded an integral heat ranging between 900 and 1020 kJ kg−1 with a very slow heat release lasting for even 12–14 h. The zeolite-based materials generated between 350 and 950 kJ kg−1 more rapidly (up to 6–7 h), depending on the nature and the content of compensating cations, as well as on the dehydration state achieved during regeneration. With the laboratory-scale test rig, the efficiency of heat extraction by convection was about 65% for Na-13X and only 38% for PBA, and it diminished with decreasing flow rate.

Keywords

• short-term thermochemical heat storage
• water vapor adsorption
• porous adsorbents
• cation-exchanged zeolites
• Prussian blue analogues
• integral heat of adsorption