VOC ternary mixture effect on ppb level photocatalytic oxidation: Removal kinetic, reaction intermediates and mineralization

Abstract

This work addresses photocatalytic oxidation for indoor air purification and more especially the key and realistic issue of VOC mixture treatment. The VOC mixture effect needs to be investigated since indoor air contains several tens of VOCs which may impact photocatalytic oxidation performances. In order to be closer to realistic conditions, concentrations in the ppb range were used and toluene, decane and trichloroethylene (TCE) were treated first as single compounds, then as an equimolar ternary mixture under the same experimental conditions. In a 120 L batch reactor, VOC removal kinetics, reaction intermediates and CO 2 mineralization are addressed using dedicated analytical devices compliant with typical ppb level monitoring. Regarding removal kinetics, the mixture effect affects the three VOCs. Regarding toluene and decane removal kinetic, the mixture effect is evidenced as mostly equivalent to a concentration effect, however TCE kinetic is further impacted. From the reaction intermediate point of view, the accurate monitoring of transiently produced intermediates evidences for the first time cross-reactivity between reaction intermediates originating from different primary VOCs. This phenomenon leading to novel reaction intermediate is mostly induced by chlorinated species produced by TCE degradation but remains moderate. An increase in VOC initial concentration to upper ppb levels emphasized a sequential degradation of primary VOC which may be related to competitive adsorption even on such a low concentration range. Finally, even if the mixture effect delays the removal of the primary VOCs, mineralization is slightly modified and, unlike formerly reported experiments on ppm range, final mineralization rates are equivalent under single or mixture condition at ppb levels. This work highlights the fact that photocatalytic treatment of VOC mixtures cannot be directly extrapolated from single VOC behaviour even at ppb level.

Abatement of ammonia and butyraldehyde under non-thermal plasma and photocatalysis: Oxidation processes for the removal of mixture pollutants at pilot scale

“…In this experiment, competition adsorption of pollutants on the photocatalysts active sites. This behavior is similar to what it was reported by Debono et al [37]. The latter evidenced the inhibitive effect along the photocatalytic degradation of three VOCs mixture.…”

Indoor air treatment of refrigerated food chambers with synergetic association between cold plasma and photocatalysis: Process performance and photocatalytic poisoning

“…This can be attributed to the reactive species generated in the reaction medium. This will not be further discussed in the present study and more details can be found in the literature and in our previous publications [33][34][35][36]. Figure 7 shows the RE for a pure and mixed system in the presence of the photocatalyst and the light source.…”

“…The degradation dynamics of the two pollutants separately seems to happen faster than when they are mixed. It is likely that this is linked to the competition of pollutants on the active sites of photocatalyst [34]. combined process, the RE reaches a value higher than 60% for a voltage equal to 9 kV.…”

Influence of operating parameters on the single-pass photocatalytic removal efficiency of acrylonitrile

“…To study the promptness of conversion of a compound and its reaction intermediates to CO 2 , Debono et al [70] suggested that the mineralization rates be plotted as a function of the conversion rates. The results are acrylonitrile conversion rate vs mineralization rates for the three concentrations studied are shown in Fig.…”