A mechanistic study of pulsed corona processing of hydrocarbons in air at ambient temperature and pressure

A large wire/cylinder bench-top corona reactor has been developed for mechanistic studies of the decomposition of volatile organic compounds (VOCs) in air at room temperature and pressure induced by different types of corona. A model hydrocarbon, n-hexane, was used to chemically characterize the process induced by positive pulsed corona, by monitoring efficiency, products and reactive intermediates in dry as well as humid air. Chemical diagnostics included qualitative and quantitative GC/FID, GC/MS and on-line FT/IR analyses which provided coherent data and mass balance for all volatile products and intermediates: CO2, CO, minor quantities of organic byproducts (propane, butane and simple aldehydes, ketones and alcohols) but also a few more complex oxygen and nitrogen-containing compounds. A considerable amount of carbon is unaccounted for, thus indicating that non-volatile products, not detected by GC analyses, are also formed. Interestingly, the extent of undetected carbon depends on the extent of VOC conversion. Thus, CO2 production increases with energy density also after complete n-hexane consumption. Humidity has a beneficial effect on hydrocarbon processing with positive pulsed corona: an increment in efficiency of 30% is gained in going from dry air to humid air with 40%RH. The most important neutral reactive species, O(3P) for dry air and •OH for humid air, were also investigated using chemical probes (ozone formation and CO oxidation, respectively). The results are consistent with the proposal that the decomposition of hydrocarbons induced by +pulsed corona is initiated by radical reactions. A preliminary comparison with results obtained with +DC corona is also presented.