(254p) Effect of Regeneration Purge Gas Oxygen Impurity on Irreversible Adsorption of Volatile Organic Compounds

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 1,2,4-trimethylbenzene (TMB) and 2-butoxyethanol (BE) as adsorbates. Nitrogen with different oxygen concentrations (â?¤ 5, 625, 1250, 2500, 5000, and 10,000 ppm) was used as regeneration purge gas during thermal desorption of TMB. Cumulative heel formation increased from 0.5% to 13% as the oxygen concentration in the desorption purge gas increased from â?¤ 5 ppm to 10,000 ppm, respectively. Thermogravimetric analysis of the regenerated samples showed extensive chemisorption of TMB when exposed to â?¥ 625 ppm oxygen in the purge gas. Regeneration of BAC performed with the highest oxygen concentration in the purge gas (10,000 ppm) showed negligible heel formation for adsorbed BE (1.3%) compared to TMB (13%). 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.