ADSORPTION PROPERTIES OF HIGH-SILICA ZEOLITES FOR HIGH-TEMPERATURE CHEMICAL HEAT-PUMPS

To evaluate their usability as adsorbents in chemical heat pumps for high-temperature use (over 373 K), an accelerated aging test by steam was performed for various zeolites and the adsorption equilibrium of selected zeolites were measured. From the high-temperature steaming test it was found that high-silica zeolites like Na-mordenite, USY (ultrastable Y) and HY had higher thermal stability than conventional A- or X-type zeolite. Further, measurements of isotherms of Na-mordenite and USY showed that they maintained adsorption capacity even at 473 K. Acquired isosters of each zeolite and water were approximated as straight lines in the range from room temperature of 473 K. On their charts, heat transformers (chemical heat pump) cycles that work at high temperatures could be generated. High-silica zeolites like Na-mordenite or USY are therefore expected to be usable as adsorbents of water for repeating chemical heat pump operations at high temperature, though their total adsorption capacities are smaller than those of A- or X-type zeolites.