184 research outputs found
Ultrasound in gasâliquid systems: Effects on solubility and mass transfer
The effect of ultrasound on the pseudo-solubility of nitrogen in water and on gasâliquid mass transfer kinetics has been investigated in an autoclave reactor equipped with a gas induced impeller. In order to use organic liquids and to investigate the effect of pressure, gasâliquid mass transfer coefficient was calculated from the evolution of autoclave pressure during gas absorption to avoid any side-effects of ultrasound on the concentrations measurements. Ultrasound effect on the apparent solubility is very low (below 12%). Conversely ultrasound greatly improves gasâliquid mass transfer, especially below gas induction speed, this improvement being boosted by pressure. In typical conditions of organic synthesis: 323 K, 1100 rpm, 10 bar, kL a is multiplied by 11 with ultrasound (20 kHz/62.6 W). The impact of sonication is much higher on gassing out than on gassing in. In the same conditions, this enhancement is at least five times higher for degassing
Refractory compounds abatement by adsorption and oxidative catalytic regeneration on activated carbon Experimental and modelling of competitive adsorption
Experimental and modelling of competitive adsorptio
Adsorption of aqueous organic mixtures on activated carbon: experiments and modelling of competitive adsorption
Experiments and modelling of competitive adsorptio
Spectral-Spatial Method for Hyperspectral Image classiïŹcation in Noisy Environment
International audienc
Competitive adsorption of p-hydroxybenzoic acid and phenol on activated carbon : experimental study and modelling.
The competitive adsorption of phenol and p-hydroxybenzoic acid (4HBA) has been investigated on activated carbon (AC) for a wide range of concentrations under unbuffered conditions. The results show a preferential adsorption of 4HBA which can be explained by the lower solubility of 4HBA and the electrostatic interactions between the AC and the ionic form of the molecule in this range of pH. The Langmuir isotherm is found suitable to describe the single-component adsorptions, indicating a monolayer adsorption in accordance with the microporous nature of the AC. Then the empirical extended Langmuir model and the predictive Ideal Adsorption Solution Theory model have been compared for competitive adsorption. When using parameter values optimized for single pollutants, both models show rather poor agreement with mixture data. However after fitting the extended Langmuir parameters with the whole data set, better results can be obtained, showing that there is some peculiar behaviour of the mixture under oxic conditions, probably tied to the effect of 4HBA on the irreversible adsorption of phenol
Photocatalytic degradation of an azo-dye on TiO2/ activated carbon composite material
A sequential adsorption/photocatalytic regeneration process to remove tartrazine, an azo-dye in aqueous solution, has been investigated. The aim of this work was to compare the effectiveness of an adsorbent/photocatalyst composite â TiO2 deposited onto activated carbon (AC) â and a simple mixture of powders of TiO2 and AC in same proportion. The composite was an innovative material as the photocatalyst, TiO2, was deposited on the porous surface of a microporous-AC using metal-organic chemical vapour deposition in fluidized bed. The sequential process was composed of two-batch step cycles: every cycle alternated a step of adsorption and a step of photocatalytic oxidation under ultra-violet (365 nm), at 25âŠC and atmospheric pressure. Both steps, adsorption and photocatalytic oxidation, have been investigated during four cycles. For both materials, the cumulated amounts adsorbed during four cycles corresponded to nearly twice themaximumadsorption capacities qmax proving the photocatalytic oxidation to regenerate the adsorbent. Concerning photocatalytic oxidation, the degree of mineralization was higher with the TiO2/AC composite: for each cycle, the value of the total organic carbon removal was 25% higher than that obtained with the mixture powder. These better photocatalytic performances involved better regeneration than higher adsorbed amounts for cycles 2, 3 and 4. Better performances with this promising material â TiO2 deposited onto AC â compared with TiO2 powder could be explained by the vicinity of photocatalytic and AC adsorption sites
Monitoring indoor air quality in French schools and day-care centres. Results from the first phase of a pilot survey
International audienceIndoor air quality surveillance in public premises, especially those hosting vulnerable populations such as children, was introduced in the second French national environment and health action plan and then regulated by the first "Grenelle Environnement" law, on August 3rd, 2009. A national pilot monitoring survey of indoor air quality in 310 French schools and day-care centres was performed in two phases from 2009 to 2011. The results of the first phase show that air quality is overall acceptable in 90% of the establishments with respect to the management values suggested by the French committee for public health. Nonetheless, a few cases required additional diagnoses or corrective measures. Furthermore, air stuffiness (based on CO2 measurements) was found to be very high in 16% of the classrooms. The Mayors and School Principals were informed and provided with means to identify the main sources of pollution and to implement remediation actions
Adsorption Competitive du Phenol et de l'Acide Phydroxy Benzoique sur Charbon Actif
Le traitement des rejets industriels constitue actuellement un problĂšme Ă©cologique majeur. Certains composĂ©s organiques, le plus souvent aromatiques de type phĂ©nols, prĂ©sents dans ces effluents industriels ne peuvent pas ĂȘtre traitĂ©s par les stations dâĂ©puration conventionnelles car leur toxicitĂ© perturbe le traitement par voie biologique. Un prĂ©traitement devient alors nĂ©cessaire conduisant au dĂ©veloppement de procĂ©dĂ©s variĂ©s dont le procĂ©dĂ© ADOX,
proposĂ© par le LGC Toulouse, basĂ© sur une adsorption sur charbon actif suivie dâune oxydation catalytique dĂ©polluante et rĂ©gĂ©nĂ©rant le charbon. Ce travail sâinscrit dans la premiĂšre Ă©tape dâadsorption de ces composĂ©s aromatiques sur charbon actif.
Les eaux industrielles contiennent en gĂ©nĂ©ral plusieurs composĂ©s organiques aromatiques. Or,la plupart des Ă©tudes relatives Ă lâadsorption sur charbon actif ont Ă©tĂ© effectuĂ©es sur des eaux synthĂ©tiques Ă un seul constituant comme le phĂ©nol par exemple. Afin de nous rapprocher de
la composition dâeffluents rĂ©els et de quantifier la compĂ©tition dâadsorption entre diffĂ©rents composĂ©s dĂ©rivĂ©s, nous avons choisi dâĂ©tudier un mĂ©lange Ă deux constituants : le phĂ©nol etlâacide p-hydroxy benzoĂŻque.
Au cours de cette Ă©tude, les deux adsorptions sont dâabord Ă©tudiĂ©es sĂ©parĂ©ment. Nous avons obtenu les dynamiques dâadsorption Ă diffĂ©rentes concentrations, pour deux types de charbon actif et pour des diamĂštres de grains variables. A 298 K, ces deux constituants prĂ©sentent des dynamiques dâadsorption sensiblement diffĂ©rentes alors que leur structure chimique est proche. Lâadsorption du phĂ©nol atteint rapidement lâĂ©quilibre laissant supposer
une adsorption mono-couche, essentiellement limitĂ©e par la diffusion dans les pores, alors quelâacide p-hydroxy benzoĂŻque prĂ©sente une adsorption plus poussĂ©e avec une cinĂ©tique pluslente reflĂ©tant ainsi un mĂ©canique plus complexe.
Ces premiers rĂ©sultats nous ont permis dâestimer les coefficients de diffusion de chaque espĂšce et dâĂ©tablir les isothermes dâadsorption. Pour le phĂ©nol, selon le type de charbon,lâisotherme peut prĂ©senter un palier. En effet, Ă partir dâune certaine valeur de la concentration la quantitĂ© de phĂ©nol adsorbĂ© est maximale et le charbon est saturĂ©. Ce phĂ©nomĂšne a permis de montrer que le modĂšle de prĂ©vision de Langmuir est plus adaptĂ© que celui de Freundlich pour ce type de charbon.
Dans la seconde partie de cette Ă©tude, nous avons Ă©tudiĂ© plusieurs mĂ©langes dâacide phydroxy benzoĂŻque et de phĂ©nol. Nous avons choisi de mettre en Ă©vidence lâinfluence de la
prĂ©sence de lâacide p-hydroxy benzoĂŻque sur lâadsorption du phĂ©nol et sur lâadsorption totale.
Les rĂ©sultats obtenus ont montrĂ© lâimportance du phĂ©nomĂšne de compĂ©tition dâadsorption et ont confirmĂ© une diffĂ©rence de mĂ©canisme dâadsorption entre les deux composĂ©s aromatique
Etude de l'adsorption compétitive de composés organiques pour le traitement des eaux résiduaires industrielles par le procédé ADOX
La problĂ©matique des eaux contenant des composĂ©s peu biodĂ©gradables et rĂ©fractaires aux traitements oxydatifs conventionnels a conduit au dĂ©veloppement de procĂ©dĂ©s innovants. Parmi eux, le procĂ©dĂ© ADOX a dĂ©jĂ dĂ©montrĂ© ses potentialitĂ©s en terme de rĂ©acteur multifonctionnel. Ce procĂ©dĂ© couple dans un seul et mĂȘme contacteur, lâadsorption et lâoxydation catalytique. Le solide utilisĂ©, du charbon actif, joue successivement le rĂŽle de lâadsorbant Ă tempĂ©rature ambiante puis de catalyseur lors de la phase dâoxydation Ă haute pression et tempĂ©rature. Lors du cycle dâadsorption, le polluant cible se trouve en compĂ©tition avec les sous-produits de la rĂ©action dâoxydation. LâĂ©tude de cette adsorption compĂ©titive est prĂ©sentĂ©e ici avec deux approches : la premiĂšre est basĂ©e sur des essais en rĂ©acteur batch, la seconde est basĂ©e sur lâĂ©tude prĂ©dictive des Ă©quilibres dâadsorption par la thĂ©orie de la solution adsorbĂ©e idĂ©ale (IAST). Deux mĂ©langes binaires ont Ă©tĂ© choisis: un mĂ©lange d'acide para-hydroxy benzoĂŻque et de dimĂ©thyl phĂ©nol et un mĂ©lange d'acide para-hydroxy benzoĂŻque et de phĂ©nol. Pour chaque mĂ©lange binaire, diffĂ©rentes proportions molaires ont Ă©tĂ© utilisĂ©es : proportions Ă©quimolaires (50%-50%) et non Ă©quimolaires (30%-70% et 70%-30%). Le charbon actif utilisĂ© est un adsorbant commercial granulaire de type micro-mesoporeux. Les solutions ont Ă©tĂ© analysĂ©es par HPLC/dĂ©tecteur UV. Les rĂ©sultats expĂ©rimentaux sur les cinĂ©tiques dâadsorption en mode compĂ©titif sont rapides, assimilables Ă un ordre 1 et tout Ă fait comparables aux comportements en corps purs. Les rĂ©sultats expĂ©rimentaux montrent que la capacitĂ© dâadsorption des molĂ©cules ayant une bonne affinitĂ© avec le charbon reste la mĂȘme, que cela soit en corps pur ou en mĂ©lange. Les groupements de surface semblent jouer ici un rĂŽle prĂ©pondĂ©rant. Sur certains mĂ©langes, une inversion de sĂ©lectivitĂ© est observĂ©e lorsque la proportion des deux composĂ©s dans le mĂ©lange est inversĂ©e, en particulier pour les eaux faiblement concentrĂ©es. La modĂ©lisation prĂ©dictive par le modĂšle IAST donne des rĂ©sultats en bon accord avec les expĂ©riences lorsque les mĂ©langes sont Ă©quimolaires. Dans le cas contraire, le modĂšle prĂ©voit de façon qualitative le comportement du mĂ©lange mais lâinversion de sĂ©lectivitĂ© constatĂ©e expĂ©rimentalement sur certains mĂ©langes non-Ă©quimolaires nâest pas trouvĂ©e par le modĂšle. Dans ces cas, les limites du modĂšle idĂ©al sont atteintes et, pour rendre compte des interactions entre les molĂ©cules, la thĂ©orie de la solution adsorbĂ©e rĂ©elle (RAST) devrait conduire Ă de meilleurs rĂ©sultats
Sequential adsorption photocatalytic oxidation process for wastewater treatment using a composite material TiO2/activated carbon
A composite material was tested to eliminate phenol in aqueous solution combining adsorption on activated carbon and photocatalysis with TiO2 in two different ways. A first implementation involved a sequential process with a loop reactor. The aim was to reuse this material as adsorbent several times with in situ photocatalytic regeneration. This process alternated a step of adsorption in the dark and a step of photocatalytic oxidation under UV irradiation with or without H2O2. Without H2O2, the composite material was poorly regenerated due to the accumulation of phenol and intermediates in the solution and on TiO2 particles. In presence of H2O2, the regeneration of the composite material was clearly enhanced. After five consecutive adsorption runs, the amount of eliminated phenol was twice the maximum adsorption capacity. The phenol degradation could be described by a pseudo first-order kinetic model where constants were much higher with H2O2 (about tenfold) due to additional OH radicals. The second implementation was in a continuous process as with a fixed bed reactor where adsorption and photocatalysis occurred simultaneously. The results were promising as a steady state was reached indicating stabilized behavior for both adsorption and photocatalysis
- âŠ