Purge gas humidity improves microwave-assisted regeneration of polymeric and zeolite adsorbents

Abstract

Microwave (MW) heating can be an effective method for adsorbent regeneration; however, it is limited to adsorbents with high MW absorption ability. In this study, two low MW absorption adsorbents (a beta type zeolite and a hyper-crosslinked polystyrene resin) were regenerated using MW heating to study the effect of purge gas humidity on MW absorption. Water saturation of the purge gas used during MW heating enhanced MW absorption by the adsorbent bed. The zeolite, a hydrophilic adsorbent, showed higher interaction with water molecules in the MW field than the resin, a hydrophobic adsorbent. The interaction of water molecules with the adsorbent surface and the water vapor concentration in the purge gas were found to be the main factors governing the extent of MW heating in the studied adsorbents. MW heating using both dry and humid purge gases was utilized to desorb model polar and non-polar adsorbates (isopropanol and cyclohexane) from the adsorbents. Using water-saturated purge gas reduced the MW energy needed for the complete desorption of cyclohexane and isopropanol on the zeolite by 73 % and 61 %, respectively, and on the resin by 33 % and 25 %, respectively. Nitrogen adsorption analysis showed that BET surface area and total pore volume of adsorbents before and after MW-assisted regeneration were comparable. This study shows that using water-saturated purge gas enhances the MW regeneration of adsorbents with poor dielectric properties.