Destruction of environmental air contaminants in non-thermal, atmospheric-pressure plasmas

Air regeneration and trace contaminant control are important issues in spacecraft and space station life support systems for maintaining a habitable cabin environment. Conventional technologies such as particulate filters, activated carbon beds, chemisorbent beds, and catalytic oxidizers suffer from limitations such as the need for frequent reneration and high mass, space, and/or energy requirements. Non-thermal, atmospheric-pressure plasmas can be a cost-effective and simple alternative as these plasmas are known to break volatile organic compounds (VOCs), a very important class of trace contaminants, very efficiently. In the present work, we describe the results of the use of non-thermal, atmospheric-pressure plasmas genetrated in three plasmas reactors based on the capillary plasma electrode (CEP) design for the remediation of VOC-containing air streams. VOC concentrations of up to several hundred ppm were used. While most data were obtained for n-heptane (typical aliphatic compound) and toluene (typical aromatic compound), we also studied the plasma destruction of benzene, ethylbenzene, and xylene. Destruction rates of more than 90% could be achieved with moderate power expenditure. The main emphasis of this study was the detailed investigation of the effects of plasma reactor volume, plasma power, specific energy, initial contaminant concentration, species residence time in the plasma, treatment efficiency of single compounds vs. species mixtures, and by-product formation on the VOC destruction rates.