Microwave-Powered Thermal Regeneration of Sorbents for CO2, Water Vapor and Trace Organic Contaminants

Feasibility of the use of microwave heating to achieve fast and efficient thermal regeneration of sorbents for the removal of carbon dioxide, water vapor, and trace organics from contaminated air streams has been conclusively demonstrated. The use of microwave power offers several advantages, including: improved heat transfer, lower thermal losses, improved power utilization, and enhanced operational capabilities. During the initial research, the sorption and microwave-powered thermal desorption of acetone, trichloroethylene (TCE), carbon dioxide, and water vapor was studied at 2.45 GHz using a rectangular waveguide based test apparatus. Both activated carbon and Carbosieve S-III were identified as excellent microwave regenerable sorbents for use in the removal of airborne organics. Water loaded silica gel, Molecular Sieve 13X, and Molecular Sieve 5A were also effectively regenerated under microwave irradiation at this frequency. Molecular Sieve 5A and a carbogenic molecular sieve prepared at NASA's Jet Propulsion Laboratory were identified as viable microwave regenerable carbon dioxide (CO₂) sorbents. A sorbent bed containing multiple media was challenged with air containing 0.5% CO₂, 300 parts per million (ppm) acetone, 50 ppm TCE, and saturated with water vapor. The layered media bed was shown to effectively purify the contaminated air stream and to be completely regenerated by microwave induced heating. Spectral studies of the reflection, transmission, and phase shifts of microwaves for a variety of sorbents over the frequency range between 1.3 - 2.7 GHz were performed.