Electron-Beam Treatment of Aromatic Hydrocarbons That Can Be Air-Stripped from Contaminated Groundwater. 2. Gas-Phase Studies

Abstract

The electron-beam (EB) degradation of volatile aromatics (benzene, toluene, ethylbenzene, xylenes: BTEX) in groundwater strip gas, which in the present work has been modeled by the introduction of the desired aromatic(s) to a stream of air or another gas, such as oxygen, is initiated essentially by the addition of *OH radicals to the aromatic ring, giving rise to hydroxycyclohexadienyl radicals, which form the corresponding peroxyl radicals upon addition of oxygen. As studied in some detail with benzene as a BTEX representative, various reactions of these lead to numerous oxidation products in a cascade of reactions, including the decomposition of products under the prevailing conditions of high turnover of the initial aromatic. Importantly, hydroxycyclohexadienylperoxyl radical formation is partly reversible, and the reactions of the hydroxycyclohexadienyl radicals, which thus have a significant presence in these systems, must therefore also be taken into consideration. In the gas phase, in contrast to the aqueous phase (see Part 1), the reactions of the hydroxycyclohexadienyl radicals lead to oligomeric products that appear to contribute, in addition to ionic clusters, to nucleation for the aerosols observed. Various nitrated products, among them nitrophenols, are observed when air is used for the stripping. However, these studies did not clear the pilot plant stage, since BTEX degradation using a bioreactor carried out in parallel was so successful that the EB technology was judged to be noncompetitive. As for the latter, expensive equipment consisting of a stripper, the EB machine, and an aerosol precipitator would be required. The condensed aerosols are biorefractory and would require further treatment for detoxification.

The Green Method in Water Management: Electron Beam Treatment

“…Radiolytic processes, especially those associated with the formation of excited molecules, dissociative capture of radicals, and oxidation, can lead to the formation of cleavage products of C–C bonds as well as bonds between a carbon and a heteroatom. Under anaerobic conditions, radiolysis eliminates gaseous fragmentation products such as H 2 , CO 2 , CH 4 , N 2 , etc. ,− Under aerobic conditions, organic pollutants can undergo sequential cleavages, leading to their complete conversion to CO 2 and H 2 O or, in the presence of heteroatoms, to oxides of the corresponding elements (SI, section S1). Such a process is called mineralization.…”

Mechanistic Pathways of the Hydroxyl Radical Reactions of Quinoline. 1. Identification, Distribution, and Yields of Hydroxylated Products

“…The yields of the monohydroxylated products are significantly lower than G ( • OH) = 5.4 or the G (−Q) = 5.21. Such a discrepancy is not an unusual phenomenon. ,− In the reaction of • OH with 2‘-deoxyguanosine, the pulse radiolysis studies account for the reactivity of about 80% of the hydroxyl radicals, whereas the final product analysis accounted for only 25% of the hydroxyl radicals . A study of the reactivity of • OH with pyridine reported significantly lower yields of the three isomeric hydroxypyridines following the radiolysis of N 2 O-saturated solutions (0.13 for 3-hydroxypyridine, 0.4 for 2-hydroxypyridine, and 0.20 for 4-hydroxypyridine) .…”

Catalytic Oxidation of Xylene in Air using TiO2 under Electron Beam Irradiation

“…The oxidation of VOCs in air using EB irradiation has been studied to develop methods for purifying ventilation gases containing dilute VOCs released from paint and chemical synthesis factories/plants [1][2][3][4][5][6][7]. Aromatic hydrocarbons such as toluene and xylene, used widely as paint solvents, are oxidized under EB irradiation into volatile (gaseous) and nonvolatile (particulate) byproducts besides CO 2 and CO (CO x ) [1][2][3][6][7][8]. The byproducts must be oxidized into CO x by further oxidation because they can contribute to photochemical oxidants and SPMs in the atmosphere.…”