VOC recovery using microwave regeneration of adsorbents: Pilot-column studies

1999 
A pilot-scale column was constructed to evaluate the technical feasibility of microwave (MW) heating as a means of regenerating adsorbents for recovery of volatile organic compounds (VOCs). The 6 inch diameter moving-bed column, which has a throughput capacity of 200 lb/hr of adsorbent, is representative of a full-scale component of a small-capacity recovery system or a single element of a large-capacity system. Regeneration experiments were conducted to study the effects of key process variables, including adsorbent and stripping gas feed rates, initial adsorbent coverage and microwave power input, on column performance. Two adsorbents with contrasting dielectric loss characteristics were studied, Dowex Optipore L502 (low dielectric loss styrene-based) and Rohm and Haas Ambersorb 600 (moderate dielectric loss carbonaceous). Adsorbates included polar and nonpolar compounds: isopropyl alcohol (iPA), methyl ethyl ketone (MEK) and toluene. Solvent recovery rates of 20--30 lbs/hr were achieved. The results of the pilot-column experiments demonstrate that axial temperature and desorption profiles are dependent on the dielectric characteristics of the adsorbent/sorbate pair, and that final regeneration coverage can be correlated with a dimensionless stripping gas ratio and final adsorbent temperature. Implications for design of microwave-regenerated VOC recovery systems are discussed.
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