Photocatalytic Degradation of Polynitrophenols on Various Commercial Suspended or Deposited Titania Catalysts Using Artificial and Solar Light

Phenol (PH) and three polynitrophenols (4-nitrophenol (PNP), 2,4-dinitrophenol (DNP), 2,4,6-trinitrophenol (TNP)) were photocatalytically degraded by using titania under either artificial or solar light. These four reactions were chosen as test reactions to compare the efficiencies of two suspended commercial titania photocatalysts (Degussa P-25 and Millennium PC-500). It appears that P-25 has a higher initial efficiency in all nitrophenol disappearance reactions. However, for the overall degradation rate, measured by the chemical oxygen demand (COD) disappearance, the performance of PC-500 was similar to that of P25. This was attributed to a favorable textural effect since PC-500 has a much higher surface area which facilitates the readsorption of intermediates. PC-500 was subsequently supported on a special photoinert paper provided by Ahlstrom Company (38-Pont Evèque, France). The influence of the silica binder used for sticking titania particles on the paper fibers was put in evidence as an inhibitor of the coulombic adsorption of anionic species, especially 2,4,6-trinitrophenol, because of the low pzc of silica. Once validated, this supported photocatalyst was introduced in an autonomous solar pilot photoreactor identical to the several prototypes built in the European AQUACAT program. It was demonstrated that the purification of water could be efficiently obtained in a larger scale without any final tedious filtration

Photodegradation mode of stearic acid crystal on heterogeneous anatase/amorphous titania films observed by differential interference contrast microscopy

International audienceReflected-light differential interference contrast microscopy was used to observe the disappearance of stearic acid crystal (B-polymorph) deposited onto a heterogeneous anatase/amorphous titania film upon ultraviolet light exposure. Microstructural studies of the films demonstrate the formation of anatase microdomains with sub-micrometric size randomly distributed throughout the amorphous surface of the film. The microscopy images reveal that the disappearance of stearic acid crystal is initiated in the immediate vicinity of these microdomains located within the crystal or close to its edges. The stearic acid disappearance proceeds via lateral growth and coalescence of pits in shape of flattened-hexagons showing a preferential orientation with respect to the stearic acid crystal symmetry. This latter fact, which is observed for the first time to the best of our knowledge, is explained by the dependence on crystallographic orientation of the progression rate of the pit edges. To justify the observed photodegradation mode, we first invoke the ultraviolet-induced formation of radical species at the anatase microdomains and their diffusion towards the pits edges. Then, the geometry and the preferential orientation of the pits are discussed in terms of anisotropy of intermolecular interactions within the crystal. These results suggest that the energy barrier seen by the radical species reaching the pit edges is correlated to the crystallographic orientation with consequences on the reaction kinetics

Comparative life cycle assessment of eight alternatives for hydrogen production from renewable and fossil feedstock

International audienceThe objective of this study is to conduct a comparative life cycle assessment of eight hydrogen production scenarios. The analysis enables a comparison of the sustainability performance of H-2 production alternatives, as well as the identification of the key elements of each option. The scenarios investigated are based on (1) fossil CH4 reforming processes, namely steam reforming, partial oxidation and auto-thermal reforming; (2) biological CH4 reforming, i.e., steam CH4 reforming, partial oxidation and auto-thermal reforming; and (3) bioethanol-to-hydrogen systems, namely steam reforming and auto-thermal reforming. The assessment is carried out with the SimaPro 7.1 program. Both CML baseline 2000 and Eco-indicator 99 are used as life cycle impact assessment methods. The results indicate that the biomethane reforming systems have the lowest impact of all of the systems. The fossil CH4 reforming scenarios produce the highest emissions of global warming gas and have the greatest contribution to the abiotic depletion potential impact. Although wheat-derived bioethanol is considered to be a biofuel, bioethanol-to-hydrogen production systems have a higher impact than fossil CH4 on acidification, eutrophication, ozone layer depletion and toxicological impacts. This research provides regulators and policy makers with a basis upon which to guide further research and development in the H-2 sector

Analyse de cycle de vie exergétique de systèmes de production d'hydrogène

Considéré comme vecteur énergétique du futur, l'hydrogène semble être la solution miracle pour sortir de la crise énergétique et environnementale actuelle. Ceci peut être vrai à condition de résoudre tous les problèmes inhérents à son cycle de vie (production, distribution, stockage et utilisation). Face aux nombreux impacts environnementaux générés au cours de la production d hydrogène, la complexité de leur évaluation et les éventuelles interactions entre eux, le recours à des méthodes d évaluation environnementale semble nécessaire. Ainsi, l Analyse de Cycle de Vie Exergétique (ACVE) a été choisie comme l outil le plus intéressant pour l étude des scénarios de production d hydrogène. Elle va, d une part, comparer des systèmes de production d hydrogène dans le but de déterminer lequel est le plus éco-efficace et, d autre part, localiser leurs possibilités d amélioration environnementale. Huit scénarios de production d hydrogène ont été étudiés par cette approche ACVE. Ces scénarios se basent essentiellement sur des techniques de reformage du méthane fossile, du biométhane et du bioéthanol. Les résultats obtenus montrent que les scénarios de production d hydrogène à partir du méthane fossile, technique mûre et largement utilisée, sont les plus gros consommateurs de ressources abiotiques et les plus émetteurs de gaz à effet de serre (GES). Par contre, le recours au biométhane comme source d hydrogène peut présenter, dans certaines configurations, une bonne solution. Le profil environnemental d une filière hydrogène ex-biométhane peut encore être rendu plus attrayant par amélioration du système de digestion anaérobie avec un système de reformage sur site. Le recours au bioéthanol produit à partir du blé comme source d hydrogène présente des effets néfastes sur l environnement. En effet, ces procédés sont caractérisés par de grands pouvoirs d eutrophisation et d acidification en plus de leurs émissions importantes des gaz effet de serre (GES). Toutefois, le bioéthanol peut constituer une source durable et renouvelable pour la production d hydrogène si sa production ne nuit pas à l environnementConsidered as the future energy carrier, hydrogen appears to be the miracle solution to overcome the current energy crisis and environmental problems. This can be possible only by solving all the problems associated with its life cycle (production, distribution, storage and final use).Due to the large number of environmental impacts generated during hydrogen production, the complexity of their evaluation and the possible interactions among them the use of environmental assessment methods is necessary. The Exergetic Life Cycle Assessment (ELCA) approach was chosen as the most useful tool for hydrogen production scenarios investigation. It compares hydrogen production systems in order to identify which one is more eco-efficient and recognizes their opportunities for environmental improvement. Eight scenarios for hydrogen production were studied by the ELCA approach. These scenarios are essentially based on reforming techniques of fossil methane, biomethane and bioethanol. The results show that the hydrogen produced by fossil methane scenarios, a mature and widely used technique, are the largest consumers of abiotic resources and emitters of greenhouse gases (GHG). The use of biomethane as hydrogen source presents an interesting solution. The environmental profile of a hydrogen ex-bio-methane can be made even more attractive solution by improving anaerobic digestion system with on-site reforming process. The use of bio-ethanol produced from wheat as a hydrogen source has large environmental impacts. In fact, these processes are characterized by large eutrophication and acidification potentials in addition to their emissions of large amount of greenhouse gases (GHG). However, bio-ethanol can be a sustainable and renewable source for hydrogen production on condition that it is produced by environmentally friendly mannersNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF