Treatment of Low Concentrations of Volatile Organic Compounds by Non-thermal Plasma

Abstract

Non-thermal plasma (NTP) technology is an emerging method to degrade otherwise recalcitrant volatile organic compounds (VOCs) in air. Here, a dielectric barrier discharge (DBD) NTP was used to evaluate the degradation efficiency of several VOCs (toluene, benzene, ethylbenzene, MEK (methyl ethyl ketone), MTBE (methyl-tert-butyl ether) 3-pentanone and n-hexane) under constant experimental conditions (6.6 L/min, 95 and 100 ppm average inlet concentrations). The efficiency with which toluene, ethylbenzene, benzene, MEK, MTBE, 3-pentanone, and n-hexane were removed was 74.03 ± 0.30%, 80.94 ± 0.07%, 57.82 ± 0.06%, 50.00 ± 0.20%, 80.00 ± 1.40%, 76.00 ± 1.4%, and 90.00 ± 0.30 %, respectively, at an inlet concentration 95 ppm, gas flow rate 6.6 L/min, and a specific input energy (SIE) of 350 J/L. The effects of various operating conditions on pollutant removal were investigated. Interestingly, the highest removal efficiencies were observed for compounds that have the highest percentage of hydrogen in the molecular structure. During treatment of toluene and ethylbenzene, a deposit was formed inside the plasma reactor. This deposit was dark brown in color and gave off an oil-like odor, suggesting the formation of higher-order hydrocarbon compounds. The deposit mass was quantified and the impact of the deposit on the DBD reactor performance was discussed. It was noted that the time required for the deposit to clog the reactor depended on the experimental conditions. The clogging time when treating toluene in dry air conditions was more than 1.5 times greater than under humidified conditions (30% RH), suggesting that attention to the treated air relative humidity is critical. The quantity and structure of the deposits depended on both input VOC molecular structure as well as the experimental conditions. Thus, this study provides recommendations for the current applications of this technology.