Abatement of Volatile Organic Compounds via a DC Arc Plasma Discharge

Due to its enclosed nature, spacecraft habitat air quality is a topic of utmost importance in which NASA places great emphasis for crew safety. Numerous potential sources of air contaminants exist for current and proposed crewed space vessels including cleaning solvents, hygiene products, lubricants, coatings, and coolants, to name a few. NASA maintains a list of 56 air contaminants that are ubiquitous to spacecraft operations codified in the Spacecraft Maximum Allowable Concentrations (SMAC) list. Most items on the SMAC list are volatile organic compounds (VOCs). For the work reported here, the authors developed a DC arc discharge plasma system wherein a test gas containing a VOC was recirculated through the plasma discharge. During the recirculation, small aliquots of the VOC were collected and analyzed via gas chromatography/mass spectrometry to quantify the reduction in VOC concentration over time. Five VOCs were analyzed (benzene, pentane, acetone, ethanol, and Freon-113) in two different background gases (CO₂ and N₂). The reactions obeyed first-order rate kinetics in all cases, and VOC concentrations were reduced to below detection limits (<~1 ppm) within 5 minutes of plasma treatment. Rate constants and half-lives were also determined for each analyte.