11 research outputs found
Adsorption of Acetone / Heptane Gaseous Mixtures on Zeolite Co-Adsorption Equilibria and Selectivities
In the present study, co-adsorption of gaseous n-heptane and acetone is studied. The adsorbent is a commercial hydrophobic zeolite. Breakthrough curves and isotherms are measured for three different acetone/heptane mixture ratios and for pure components. Zeolites showed a greater adsorption capacity for acetone alone than for heptane alone. For the mixtures, the majority component was the most adsorbed. Zeolites have a good selectivity for acetone even though acetone is more volatile than heptane. Specific adsorption sites are reserved for acetone adsorption and are not accessible to heptane. The polarity of a component leads to electrostatic interactions with cation exchange. On non-specific adsorption sites, acetone can be displaced by heptane, which is less volatile. Moreover, experiments show that selectivity depends on the ratio of the mixture. For co-adsorption of a mixture of polar and non-polar components, selectivity depends on relative polarity, mixture ratio, and boiling point
Measurement and Modeling of Single- and Multi-Component Adsorption Equilibria of VOC on High-Silica Zeolites
From pure and binary gas adsorption equilibria measurements carried out using a volumetric method for three volatile organic compounds (methyl ethyl ketone, toluene (TOL), and 1,4-dioxane) on two high-silica zeolites, desaluminated faujasite Y (Fau Y) and ZSM-5 (Sil Z), co-adsorption was investigated and modeled. Apart from steric exclusion taking place with TOL-containing mixtures on Sil Z, micropore filling was similar to distillation since the component with the lower volatility adsorbed preferentially. At low coverage, chemisorption on specific sites happened in favor of polar or major compound, whereas at saturation the adsorbent was selective for the minor compound. Second, a quantitative prediction of binary equilibria was performed using the ideal adsorbed solution theory (IAST), examining the influence of pure component adsorption fitting model. The efficiency of correlations when extending AST to real mixture behavior was satisfactory in most cases. For engineering purposes, Fau Y is to be considered as a high-adsorption capacity adsorbent, whose selectivity can be described qualitatively by the distillation analogy and predicted quantitatively with the IAST in case of quasi-ideal mixtures
Mass Transfer in VOC Adsorption on Zeolite : Experimental and Theoretical Breakthrough Curves
From experimental results of adsorption of volatile organic compounds (VOCs) on zeolite, we propose simulations of the breakthrough curves based on the Linear Driving Force model. Experiments were run on fixed beds of hydrophobic commercial zeolites. Pollutants chosen are from several chemical classes with different polarities. A good agreement between experimental and numerical results is found when an adjustable value of the internal mass-transfer coefficient is used. A constant value of effective diffusivity is found independent of the nature and the amount of VOCs adsorbed. A relation linking intrapellet mass-transfer coefficient and equilibrium constant is proposed, including the average effective diffusivity, to make predictions of breakthrough curves for any kind of volatile organic pollutant in gaseous effluent
Regeneration of High Silica Zeolites via Advanced Oxidation ProcessesâA Preliminary Study About Adsorbent Reactivity Toward Ozone
Aiming at regenerating adsorbents, the reactivity toward ozone of two high silica zeolites (HSZ), a dealuminated faujasite Y (Fau Y) and a silicalite (Sil Z), was investigated. In case of Fau Y, no physical adsorption occurred but a total degradation of ozone. This phenomenon was attributed to an active sites-role of silanol groups (SiOH), mainly developed by the dealumination step. In contrast, the ozone adsorption in the smaller channels of Sil Z was important (about 17 mmol gâ1), but when a certain local concentration of ozone was reached, the ozone degradation became significant and increased up to 100%. The ozonated zeolites were regenerated in an oven. Whereas the regeneration was total at 773K, a treatment at 500K seemed insufficient since a co-adsorption phenomenon was observed with suspected nitrous oxides (NO2) as a product of ambient nitrogen oxidation. Whereas the Fau Y was not affected at all by ozonation, the adsorption capacities of Sil Z zeolite were enhanced, and it exhibited a higher selectivity for polar compound. This was attributed to a surface modification, by highly reactive species generated during molecular ozone decompositio
Procédés hybrides adsorption/oxydation en phase gazeuse (application au traitement des composés organiques volatils)
This study focuses on hybrid treatment processes of industrial air stream polluted with volatile organic compounds (VOC). It aims at increasing the general knowledge of heterogeneous catalysis but also at developing new processes for environmental protection. In the first part of this work, adsorption equilibriums of daily used industrial solvents on hydrophobic zeolites are determined for pure and binary systems. Modelling of binary mixtures competitive adsorption is carried out via a thermodynamic approach, using the Ideal Adsorbed Solution Theory and its generalized form the Real Adsorbed Solution Theory. Then, an oxidation process of VOC is developed and tested. It uses both the adsorption properties of a zeolite and the photocatalytic activity of titanium dioxide. The mixed material is firstly prepared by a Sol-Gel method, and consecutively characterized by chemical analysis, X-Ray diffraction, porous distribution determination, and adsorption properties measurements. Different operating conditions are studied and their respective influence on the global efficiency of the system are evaluated. Finally, a comparison is made with the regeneration of VOC loaded zeolites using V-UV photolysis. The great efficiency of this process is demonstrated. Both limits and further prospects directions are indicatedLe travail de thĂšse se focalise sur des procĂ©dĂ©s de traitement d'air chargĂ© en composĂ©s organiques volatils (COV). Il se situe Ă la fois dans une optique de gĂ©nĂ©ration de connaissances mais se place aussi dans le secteur Ă©conomique et plus spĂ©cifiquement dans le dĂ©veloppement de nouveaux procĂ©dĂ©s de protection de l'environnement. Dans un premier temps, les Ă©quilibres d'adsorption sur zĂ©olithes hydrophobes sont dĂ©terminĂ©s pour diffĂ©rents solvants industriels en corps purs et en mĂ©lange. La modĂ©lisation de mĂ©langes binaires par l'approche des solutions adsorbĂ©es idĂ©ales et rĂ©elles est abordĂ©e. Dans un second temps, un procĂ©dĂ© d'oxydation de COV est mis en Ćuvre et utilisĂ©. Il utilise Ă la fois les caractĂ©ristiques adsorbantes d'une zĂ©olithe et les propriĂ©tĂ©s photocatalytique du dioxyde de titane. Le matĂ©riau est tout d'abord prĂ©parĂ© par imprĂ©gnation sol-gel, puis caractĂ©risĂ© par analyse chimique, diffraction X, dĂ©termination de la micro et mĂ©soporositĂ©, et des propriĂ©tĂ©s d'adsorption. DiffĂ©rentes conditions opĂ©ratoires sont Ă©tudiĂ©es et leur influence sur les performances du systĂšmes sont discutĂ©es. Dans un dernier temps, une comparaison est effectuĂ©e avec la rĂ©gĂ©nĂ©ration des zĂ©olithes chargĂ©es en COV par photolyse V-UV. La grande efficacitĂ© de ce procĂ©dĂ© est prouvĂ©e. Les limites et les perspectives de dĂ©veloppement des procĂ©dĂ©s sont indiquĂ©esTOULOUSE-INSA (315552106) / SudocSudocFranceF
TRAITEMENT DES COMPOSES ORGANIQUES VOLATILS (COV) PAR ADSORPTION SUR ZEOLITHE. ETUDE DU COUPLAGE ABSORPTION/ADSORPTION APPLIQUE AU TRAITEMENT DE L'AIR
TOULOUSE-INSA (315552106) / SudocSudocFranceF
Procédé d'oxydation catalytique en voie humide de la pollution organique aqueuse. Traitement de composés organo-azotés
International audienceThe wet air oxidation process (WAO) is an efficient method for treating wastewaters containing nitrogenous organic compounds, providing that a composite manganese/cerium oxide (7/3 molar ratio) is used as catalyst. This allows to obtain molecular nitrogen, absolutely harmless to the environment.During preliminary tests, it was established that the temperature (about 260°C) and the catalyst concentration are the most important factors to transform ammonia into molecular nitrogen (N-N2), which is the main product while only very limited amounts of nitrites (N- N02-) and nitrates (N- NO3-) appear. In addition, neither manganese nor cerium were leached off in the solution, under the experimental conditions. This composite oxide catalyst is adapted for the direct conversion of organic nitrogen (N-Org) to molecular nitrogen (N·N2), as well as for the conversion of organic carbon (TOC) to carbon dioxide. This was clearly established during the treatment of aliphatic nitrogenous compounds (-alanine, urea) and aromatic ones (aniline, aminophĂ©nol). Ammonia nitrogen (N-NH3) is always the main intermediate product and the rate of elimination of organic nitrogen is always rapid with regard to the second reaction step (transformation of N-NHJ to N-N2), which is the limiting one in this process. To account for the results obtained, it was possible to propose a general simple scheme with two main steps for the nitrogen transformation pathway and to determine the kinetic constants. This kinetic data is to be used in a next study about industrial reactors computation.Le procĂ©dĂ© d'oxydation en voie humide (OVH) Ă l'oxygĂšne molĂ©culaire catalysĂ© par l'oxyde composite de manganĂšse/cĂ©rium (rapport molaire 7/3) constitue une solution efficace au traitement d'effluents aqueux contenant des composĂ©s organo-azotĂ©s. Il permet d'obtenir la formation d'azote molĂ©culaire (N-N2), totalement inoffensif pour l'environnement.L'Ă©tude de l'oxydation de l'ammoniaque montre que la tempĂ©rature et la concentration en catalyseur sont les facteurs prĂ©pondĂ©rants de ce procĂ©dĂ©. Des nitrites (N-N02-) et des nitrates (N-NO3-) sont obtenus, mais seulement en trĂšs faibles quantitĂ©s. L'azote molĂ©culaire est le produit principal de la rĂ©action et aucun relargage de mĂ©taux en solution n'a Ă©tĂ© observĂ©. L'oxyde composite de Mn/Ce favorise la conversion de l'azote organique (N-Org) en azote molĂ©culaire, ainsi que l'oxydation du carbone organique (COT) en dioxyde de carbone. Ce phĂ©nomĂšne a Ă©tĂ© vĂ©rifiĂ© lors du traitement de composĂ©s aliphatiques (-alanine et urĂ©e) et aromatiques (aniline et aminophĂ©nol) azotĂ©s. L'Ă©tape intermĂ©diaire de minĂ©ralisation de l'azote organique en azote ammoniacal (N-NH3) est essentielle pour la conversion finale en azote molĂ©culaire. Un schĂ©ma rĂ©actionnel en deux Ă©tapes successives rend compte du processus d'oxydation et l'Ă©tude cinĂ©tique menĂ©e a permis de dĂ©terminer les diffĂ©rentes constantes cinĂ©tiques, qui pourront ĂȘtre utilisĂ©es ultĂ©rieurement lors du calcul de rĂ©acteurs industriels d'oxydation
DĂ©termination de la pollution organique des eaux, mesure de la demande chimique en oxygĂšne
Le but de ce travail est dâillustrer les rĂ©actions dâoxydorĂ©duction Ă travers la dĂ©termination de la pollution
organique des eaux. AprÚs avoir défini la demande chimique en oxygÚne (DCO) et avoir rappelé le principe
dâun dosage spectrophotomĂ©trique, une eau contenant du saccharose est analysĂ©e. Un dosage en retour du
dichromate par le fer (II) et un dosage spectrophotométrique du chrome (III) sont réalisés. Les résultats
obtenus sont exprimés en terme de DCO
Application de l'oxydoréduction Détermination de la pollution organique des eaux, mesure de la demande chimique en oxygÚne
International audienceThe aim of this study is to illustrate the oxidoreduction reactions for the determination of the organic pollution in water. Firstly, the chemical oxygen demand (COD) is defined and the principle of the spectrophotometric dosage is remained. Then, a saccharose solution is analysed. A titration of the excess dichromate by the iron (II) and a spectrophotometric dosage of chrome (III) are performed. The results obtained are expressed in terms of COD.Le but de ce travail est d'illustrer les réactions d'oxydoréduction à travers la détermination de la pollution organique des eaux. AprÚs avoir défini la demande chimique en oxygÚne (DCO) et avoir rappelé le principe d'un dosage spectrophotométrique, une eau contenant du saccharose est analysée. Un dosage en retour du dichromate par le fer (II) et un dosage spectrophotométrique du chrome (III) sont réalisés. Les résultats obtenus sont exprimés en terme de DCO. Mots-clés Demande chimique en oxygÚne, DCO, oxydoréduction, dosage spectrophotométrique
Heterogeneous photocatalysis of butanol and methyl ethyl ketoneâcharacterization of catalyst and dynamic study
International audienceNew titanium dioxide (TiO2) based catalysts were prepared by impregnating commercial zeolites in pellets form using a solâgel technique. Characterization was done with chemical analysis, X-Ray diffraction, scanning electron microscopy, and BET measurements, together with volatile organic compounds (VOC) adsorption equilibrium experiments. TiO2 happened to fix on the inert binder leading to a close intimacy of mixing with the zeolites crystallites, without significant modification of support properties. A diffusion cell was used to produce dilute polluted air streams for dynamic experiments, in which adsorption and photodegradation phases were alternatively carried out. Regeneration of adsorbent was evaluated regarding experimental conditions. Through a comparison with the results obtained on impregnated mesoporous borosilicate beads, it was clarified that zeolite supports had no effect on 1-butanol (BuOH) photooxidation mechanisms. Yet, evidence for mass transfer limitation was found, and attributed to intracrystalline diffusion in zeolites