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

Seyed Mojtaba Hashemi
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
more » ... 1 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 alkylaromatics 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. iii Dedication I would like to dedicate this thesis to my lovely parents, Jalal and Maryam, for their continuous support and encouragement. iv Acknowledgement I would like to express my gratitude to Dr. Zaher Hashisho for his supervision, guidance and support through my research. This work could not have been accomplished without his guidance, knowledge, and passion.
doi:10.7939/r3wd3qd3q fatcat:ybfhhh7vljgtnmzfkxm5allbmi