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

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.

Automated summary

The study compared the heat release capabilities of PBA and 13X zeolites with different compensating cations, showing that PBA released heat slowly and over a longer period, while zeolite-based materials released heat more rapidly. The experimental results also indicated variations in heat extraction efficiency at different flow rates.