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Effect of Desorption Purge Gas Oxygen Impurity on Heel Formation During Regeneration of Beaded Activated Carbon Saturated with Organic Vapors Open Access


Other title
Heel formation
Purge gas
Activated carbon
Type of item
Degree grantor
University of Alberta
Author or creator
Hashemi, Seyed Mojtaba
Supervisor and department
Hashisho, Zaher (Civil and Environmental Engineering)
Examining committee member and department
Trivedi, Japan (Civil and Environmental Engineering)
Dhar, Bipro (Civil and Environmental Engineering)
Department of Civil and Environmental Engineering
Environmental Engineering
Date accepted
Graduation date
2017-11:Fall 2017
Master of Science
Degree level
Irreversible adsorption or heel formation during cyclic adsorption/regeneration of high molecular weight volatile organic compounds (VOCs) onto activated carbon decreases its adsorption capacity and lifetime. The effect of regeneration purge gas oxygen impurity on activated carbon performance, specifically during successive adsorption/regeneration cycles was investigated. 5-cycle adsorption/regeneration tests were performed on microporous beaded activated carbon (BAC) using 11 different aliphatic and aromatic organic compounds representative of VOCs produced from painting booths. Nitrogen with different oxygen concentrations (≤ 5 to 20,000 ppm) was used as regeneration purge gas during thermal desorption of 1,2,4-trimethylbenzene (TMB). Cumulative heel formation increased from 0.5% to 15.4% as the oxygen concentration in the desorption purge gas increased from ≤ 5 ppm to 20,000 ppm, respectively, in case of TMB adsorption. For regeneration of BAC saturated with all other VOCs, nitrogen with two levels of oxygen impurity (≤ 5 ppm and 10,000 ppm) was used as regeneration purge gas. At 10,000 ppm oxygen concentration, the cumulative heel was 0.7-3.2% for aliphatic compounds and 0-13% from for aromatic compounds while at ≤ 5 ppm, it was 0.3-1.3% for aliphatic compounds and 0.0-4.6% for aromatic compounds. Overall, regeneration of alkyl-aromatics was impacted by presence of oxygen in the purge gas to a greater degree compared to aliphatic compounds. Thermogravimetric analysis of the regenerated samples showed desorption of species at high temperatures (400-600°C) which shows that these compounds are strongly attached to the adsorbent surface. The results suggest that the effect of regeneration purge gas oxygen impurities on the irreversible adsorption of VOCs is dependent on the nature of the adsorbate- likely its tendency to react with oxygen. The results from this study help explain the heel formation mechanism and how it relates to regeneration purge gas purity.
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