Effect of adsorption and operating parameters on volatile organic compounds mixture photocatalytic treatment in indoor air conditions

Les Composés Organiques Volatils (COV) font partie des principaux polluants de l’air intérieur. L’oxydation photocatalytique sur TiO2 est un procédé qui permet de traiter l’air en éliminant les COV. Les objectifs de ce travail sont d’étudier (1) l’adsorption simple et compétitive des COV sur TiO2, (2) la cinétique de l’oxydation photocatalytique d’un mélange de COV, (3) l’effet de la géométrie du média photocatalytique, de l’intensité lumineuse, de la vitesse d’écoulement et de la concentration initiale sur l’efficacité du traitement. Dans le but de se rapprocher des conditions réelles du traitement de l’air intérieur, les dégradations de COV sont effectuées sous une humidité relative de 50 % et avec des concentrations initiales en COV inférieures à la ppm. Les COV étudiés sont le formaldéhyde, l’acétaldéhyde, l’acide acétique, le toluène et le décane. Les résultats montrent principalement que (1) l’adsorption des COV est affectée par l’humidité de différentes manières, ces mécanismes doivent être pris en compte lors de la modélisation de l’oxydation photocatalytique des COV en mélange, (2) les vitesses de dégradation des COV sont plus faibles en présence d’autres COV, dans les réacteurs fermés agités comme dans les réacteur dynamiques multi-passages, (3) les propriétés d’adsorption des COV permettent l’interprétation des effets de mélange, mais d’autres phénomènes participent à ces effets, (4) le contact entre l’air et le photocatalyseur joue un rôle important sur les performances du traitement photocatalytique, l’efficacité augmente lorsque le média est placé de manière à augmenter la longueur de ce contact et lorsque la vitesse d’écoulement de l’air diminue.Volatile Organic Compounds (VOCs) are major indoor air pollutants. Photocatalytic oxidation process with TiO2 enables indoor air treatment by removing VOCs. This work aims at studying (1) single and competitive VOC adsorption onto TiO2, (2) VOC mixture photocatalytic oxidation kinetics, (3) photocatalytic medium geometry, light intensity, air flow velocity and VOC initial concentrations roles in the treatment efficiency. In order to better represent real indoor air treatment conditions, the photocatalytic oxidations are performed under 50 % relative humidity and sub-ppm VOC initial concentrations. The studied VOCs are formaldehyde, acetaldehyde, acetic acid, toluene and decane. The obtained results mainly show that (1) humidity affects VOC adsorption by different ways, these mechanisms must be taken into account while modeling VOC mixture photocatalytic oxidation, (2) VOC degradation rates are lower in presence of other VOCs, in batch and multi-pass dynamic reactors, (3) VOC adsorption properties enable the VOC mixture effects interpretation, but some other phenomena play a role in these effects, (4) air and photocatalyst contact play an important role in the photocatalytic oxidation rate, efficiency increases when the flow velocity decreases and when the medium geometry change causes a longer contact between air and the photocatalyst

La problème juif : la renaissance de l'antisémitisme, l'exclusivisme juif, le judaisme et l'esprit de révolte, le judaisme et le puritanisme, assimilation ou nationalisme

par Georges Bataul

Le pontife de la démagogie, Victor Hugo / Georges Batault

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Acetaldehyde and acetic acid adsorption on TiO2 under dry and humid conditions

International audienceAdsorption plays a key role in the volatile organic compound (VOC) photocatalytic oxidation performance and kinetic behavior. It can lead to VOC mixture sequential treatment or even photocatalyst deactivation. The aim of this work is to determine qualitative and quantitative data regarding VOC adsorption on P25 TiO2. Acetaldehyde and acetic acid adsorption on TiO2 have been studied under both dry and humid conditions. Three experimental methods have been used: breakthrough curves, room temperature desorptions and temperature-programmed desorptions. First, acetaldehyde and acetic acid adsorptions are studied individually. Dry and humid experiments provide complementary pieces of information to identify the adsorption modes, in accordance with literature. The Langmuir model parameters (adsorption constant (K), reversible and irreversible maximum adsorbed amounts (q(m,rev) and q(m,irr)), and adsorption enthalpy Delta H) are determined for each VOC. Based on experimental results, a model for acetaldehyde and water co-adsorption is proposed, taking into account the specific interaction between acetaldehyde and water molecule. Regarding acetic acid, a reactive adsorption pathway is proposed and a kinetic model is developed to describe the reactive adsorption. Finally, in order to understand multi-VOC interaction on TiO2 surface, the sequential adsorption of acetaldehyde and acetic acid is investigated and confronted with the single-VOC data. As a result, single VOC adsorption parameters are useful to understand and predict multi-VOC photocatalytic oxidation. (C) 2014 Elsevier B.V. All rights reserved

Study of physico-chemical mechanisms for modeling the influence of operating conditions in a PCO indoor air treatment device

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Determination of the Clean Air Delivery Rate (CADR) of Photocatalytic Oxidation (PCO) Purifiers for Indoor Air Pollutants Using a Closed-Loop Reactor. Part II: Experimental Results

The performances of a laboratory PhotoCatalytic Oxidation (PCO) device were determined using a recirculation closed-loop pilot reactor. The closed-loop system was modeled by associating equations related to two ideal reactors: a perfectly mixed reservoir with a volume of VR = 0.42 m3 and a plug flow system corresponding to the PCO device with a volume of VP = 5.6 × 10−3 m3. The PCO device was composed of a pleated photocatalytic filter (1100 cm2) and two 18-W UVA fluorescent tubes. The Clean Air Delivery Rate (CADR) of the apparatus was measured under different operating conditions. The influence of three operating parameters was investigated: (i) light irradiance I from 0.10 to 2.0 mW·cm−2; (ii) air velocity v from 0.2 to 1.9 m·s−1; and (iii) initial toluene concentration C0 (200, 600, 1000 and 4700 ppbv). The results showed that the conditions needed to apply a first-order decay model to the experimental data (described in Part I) were fulfilled. The CADR values, ranging from 0.35 to 3.95 m3·h−1, were mainly dependent on the light irradiance intensity. A square root influence of the light irradiance was observed. Although the CADR of the PCO device inserted in the closed-loop reactor did not theoretically depend on the flow rate (see Part I), the experimental results did not enable the confirmation of this prediction. The initial concentration was also a parameter influencing the CADR, as well as the toluene degradation rate. The maximum degradation rate rmax ranged from 342 to 4894 ppbv/h. Finally, this study evidenced that a recirculation closed-loop pilot could be used to develop a reliable standard test method to assess the effectiveness of PCO devices

How chemical and physical mechanisms enable the influence of the operating conditions in a photocatalytic indoor air treatment device to be modeled

International audienceThe photocatalytic degradation of toluene in indoor air conditions was performed in a closed-loop multi-pass photocatalytic reactor using the Box-Behnken experimental design methodology. The objective of this work was to rigorously determine a kinetic model in order to understand the behavior of the reactor in real indoor air conditions and to relate the kinetic parameters to physical and chemical mechanisms. Three main parameters were studied: initial toluene concentration, light irradiance and air stream velocity. The experimental results were used to calculate the single-pass removal efficiency for different operating conditions and to establish a relationship between the single-pass removal efficiency, light irradiance and air stream velocity. This relationship was integrated into an overall reaction rate law based on the Langmuir-Hinshelwood mechanism. The kinetic model obtained was then validated for various experimental conditions

Rate law model to better understand the influence of process parameters during toluene photocatalytic degradation in indoor air conditions

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