(29d) Effect of Adsorbate Properties on Heel Formation during Regeneration of Activated Carbon

Regeneration conditions such as high heating rate, low purge gas flow rate, and other factors can lead to heel formation and adsorption capacity loss in activated carbon. This research investigates the effects of adsorbate properties on heel formation in activated carbon, under high heating rates and low purge gas flow. For this purpose, five-cycle adsorption/desorption tests were completed using eight alkyl benzenes including toluene, 1,2,4 trimethylbenzene (TMB), 1,3,5 TMB, o-xylene, p-xylene, m-xylene, isopropylbenzene, and neopentylbenzene as adsorbates. Heel formation showed differences for these alkyl benzene adsorbates with cumulative heel formation ranging from 8.9% (toluene) to 17.0% (neopentylbenzene). Thermogravimetric analysis identified adsorbate decomposition as the main heel formation mechanism in all cases, showing a highly stable heel with low removal (less than 31.5%) at temperatures as high as 800 ^oC. Higher heel formation was observed for adsorbates with high boiling point and low thermal stability (i.e., longer branches with β and γ-carbons), which provided favourable conditions for adsorbate decomposition. The results from this study contribute to a better understanding of heel formation mechanisms during activated carbon regeneration.