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 Processes—A 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 g−1), 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 thèse se focalise sur des procédés de traitement d'air chargé en composés organiques volatils (COV). Il se situe à la fois dans une optique de génération de connaissances mais se place aussi dans le secteur économique et plus spécifiquement dans le développement de nouveaux procédés de protection de l'environnement. Dans un premier temps, les équilibres d'adsorption sur zéolithes hydrophobes sont déterminés pour différents solvants industriels en corps purs et en mélange. La modélisation de mélanges binaires par l'approche des solutions adsorbées idéales et réelles est abordée. Dans un second temps, un procédé d'oxydation de COV est mis en œuvre et utilisé. Il utilise à la fois les caractéristiques adsorbantes d'une zéolithe et les propriétés photocatalytique du dioxyde de titane. Le matériau est tout d'abord préparé par imprégnation sol-gel, puis caractérisé par analyse chimique, diffraction X, détermination de la micro et mésoporosité, et des propriétés d'adsorption. Différentes conditions opératoires sont étudiées et leur influence sur les performances du systèmes sont discutées. Dans un dernier temps, une comparaison est effectuée avec la régénération des zéolithes chargées en COV par photolyse V-UV. La grande efficacité de ce procédé est prouvée. Les limites et les perspectives de développement des procédés sont indiquéesTOULOUSE-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, aminophénol). 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 procédé d'oxydation en voie humide (OVH) à l'oxygène moléculaire catalysé par l'oxyde composite de manganèse/cérium (rapport molaire 7/3) constitue une solution efficace au traitement d'effluents aqueux contenant des composés organo-azotés. Il permet d'obtenir la formation d'azote moléculaire (N-N2), totalement inoffensif pour l'environnement.L'étude de l'oxydation de l'ammoniaque montre que la température et la concentration en catalyseur sont les facteurs prépondérants de ce procédé. Des nitrites (N-N02-) et des nitrates (N-NO3-) sont obtenus, mais seulement en très faibles quantités. L'azote moléculaire est le produit principal de la réaction et aucun relargage de métaux en solution n'a été observé. L'oxyde composite de Mn/Ce favorise la conversion de l'azote organique (N-Org) en azote moléculaire, ainsi que l'oxydation du carbone organique (COT) en dioxyde de carbone. Ce phénomène a été vérifié lors du traitement de composés aliphatiques (-alanine et urée) et aromatiques (aniline et aminophénol) azotés. L'étape intermédiaire de minéralisation de l'azote organique en azote ammoniacal (N-NH3) est essentielle pour la conversion finale en azote moléculaire. Un schéma réactionnel en deux étapes successives rend compte du processus d'oxydation et l'étude cinétique menée a permis de déterminer les différentes constantes cinétiques, qui pourront être utilisées ultérieurement lors du calcul de réacteurs industriels d'oxydation

Détermination de la pollution organique des eaux, mesure de la demande chimique en oxygène

Le but de ce travail est d’illustrer les réactions d’oxydoréduction à travers la détermination de la pollution organique des eaux. Après avoir défini la demande chimique en oxygène (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

Application de l'oxydoréduction Détermination de la pollution organique des eaux, mesure de la demande chimique en oxygène

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. Après avoir défini la demande chimique en oxygène (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 oxygène, DCO, oxydoréduction, dosage spectrophotométrique

Heterogeneous photocatalysis of butanol and methyl ethyl ketone—characterization of catalyst and dynamic study

International audienceNew titanium dioxide (TiO2) based catalysts were prepared by impregnating commercial zeolites in pellets form using a sol–gel 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