A single events microkinetic model for hydrocracking of vacuum gas oil

International audienceThe single events microkinetic modeling approach is extended to include saturated and unsaturated cyclic molecules, in addition to straight chained paraffins. The model is successfully applied to hydrocracking (HCK) of a hydrotreated Vacuum Gas Oil (VGO) residue in a pilot plant, under industrial operating conditions, on a commercial bi-functional catalyst. The molecular composition of the VGO feed is obtained by reconstruction based on a combination of analytical data (SIMDIS, GCxGC, mass spectroscopy). The necessary extensions to the single events methodology, which has previously only been applied to much simpler reacting systems (i.e. HCK of paraffins) are detailed in this work. Feeds typically used in the petrochemical industry typically contain a far more complex mixture of hydrocarbons, including cyclic species (i.e. naphtenes & aromatics). A more complex reaction network is therefore required in order to apply a single events model to such feeds. Hydrogenation, as well as endo-and exo-cyclic reactions have been added to the well-known acyclic β-scission and PCP-isomerization reactions. A model for aromatic ring hydrogenation was included in order to be able to simulate the reduction in aromatic rings, which is an important feature of HCK units. The model was then applied to 8 mass balances with a wide range of residue conversion (20 – 90%). The single events model is shown to be capable of correctly simulate the macroscopic effluent characteristics, such as residue conversion, yield structure, and weight distribution of paraffinic, naphthenic, and aromatic compounds in the standard cuts. This validates the overall model. The single events model provides far more detail about the fundamental chemistry of the system. This is shown in a detailed analysis of the reaction kinetics. The evolution of molecule size (i.e. carbon number), number of saturated/unsaturated rings, or the ratio of branched and un-branched species can be followed along the reactor. This demonstrates the explanatory power of this type of model. Calculations are performed on the IFPEN high performance computing cluster, with parallelization via MPI (message passing interface). This was very useful in order to reduce time consuming problems especially for the parameter fitting step.

Kinetic Modeling of Vacuum Gas Oil Hydrotreatment using a Molecular Reconstruction Approach

International audienceVacuum Gas Oils (VGO) are heavy petroleum cuts (boiling points ranging from 350 to 550 ˚C) that can be transformed into valuable fuels (gasolines, diesels) by fluid catalytic cracking or hydrocracking. Prior to these conversion processes, hydrotreating is required in order to eliminate the impurities in VGOs. The hydrotreatment process enables to meet the environmental specifications (total sulfur contents) and to prevent nitrogen poisoning of conversion catalysts. In order to develop a kinetic model based on an accurate VGOs molecular description, innovative analytical tools and molecular reconstruction techniques were used in this work. A lumped model using a Langmuir-Hinshelwood representation was developed for hydrodearomatization, hydrodesulfurization and hydrodenitrogenation of the VGO. This lumped model was successfully applied to the experimental feed pretreatment data and was able to predict evolution of concentration of the aromatics, nitrogen and sulfur species

X-ray scattering from stepped and kinked surfaces: An approach with the paracrystal model

A general formalism of X-ray scattering from different kinds of surface morphologies is described. Based on a description of the surface morphology at the atomic scale through the use of the paracrystal model and discrete distributions of distances, the scattered intensity by non-periodic surfaces is calculated over the whole reciprocal space. In one dimension, the scattered intensity by a vicinal surface, the two-level model, the N-level model, the faceted surface and the rough surface are addressed. In two dimensions, the previous results are generalized to the kinked vicinal surface, the two-level vicinal surface and the step meandering on a vicinal surface. The concept of crystal truncation rod is generalized considering also the truncation of a terrace by a step (yielding a terrace truncation rod) and a step by a kink (yielding a step truncation rod).Comment: 33 pages, 18 figure

Growth of palladium nanoparticles on nanostructured highly ordered pyrolytic graphite

We report on the growth of palladium nanoparticles on the basal plane of as-cleaved highly oriented pyrolytic graphite (HOPG) samples, and on CO2 ion sputtered nanostructured HOPG surfaces. The morphology of Pd nanostructures grown at room temperature is investigated by scanning tunneling microscopy (STM). The STM observations indicate that the morphology of the Pd films is strongly dependent on the HOPG surface. Stabilized Pd particles only form on the sputtered surface, while ramified Pd particles decorate the clean HOPG terraces. The prestructuring of HOPG surface leads to a selective location of particles at the rim of the nanopits generated by the CO2 ion sputtering and annealing of the surface. The correlation between size, form, density, spatial distribution of the Pd nanoparticles and the quantity of metal added on surface is discussed. We also describe trench channeling of graphite or graphene basal planes by means of Pd nanoparticles in an ambient environment. Copyright (c) 2014 John Wiley & Sons, Ltd

La rénovation des collèges

The renovation of French « colleges » : from utopianism to pragmatism? - The challenge of mixed-ability classes — the consequence of establishing the same school for everybody — has made it inevitable to transform the « 1 st cycle » (middle school) and the way it is run. Such is the aim of the renovation of French « collèges » which started in 1984 and is now being widespread. Its contents vary from one school to the other but, under various forms, it tends to promote educational methods adapted to every child's abilities. The survey given here and elaborated from studies made for the Ministry of Education by the General Inspectors, shows the pros and cons. Through the recorded evolution, ranging from the enthusiastic « pioneers » to the mere undertaking of simple actions, it shows what has been achieved, what has been successful and what is yet uncertain in this experiment still on its way.Le défi de l'hétérogénéité, conséquence de la création du collège unique, a rendu inévitable la transformation du premier cycle et de son mode de fonctionnement. Tel est l'objectif de la « rénovation des collèges » engagée en 1984 et en voie de généralisation. Son contenu est variable d'un établissement à l'autre, mais il tend toujours, sous des formes diverses, à promouvoir une pédagogie différenciée. Le bilan présenté ici, à partir d'études réalisées pour les autorités ministérielles par leurs inspections générales, est nuancé. A travers l'évolution enregistrée, depuis l'enthousiasme des « pionniers » jusqu'à la simple programmation d'actions modestes, il montre les acquis, les réussites et les incertitudes d'une opération qui se poursuit.Dulot Alain. La rénovation des collèges. In: Revue française de pédagogie, volume 86, 1989. pp. 61-68

Le rôle de l’ergothérapeute dans l’accompagnement des adolescents et jeunes adultes atteints de déficience visuelle acquise dans la réalisation de leurs loisirs

Background: Acquired visual impairment occurs during life and consists in a significant decrease in the visual acuity of one or both eyes. This illness requires to relearn daily life gestures and also influences the access to leisure. The aim of this study was to explore how people with acquired visual impairment access their leisure and how occupational therapists can support them in doing so.Method: Through a qualitive method, two occupational therapists working with a visually impaired population were interviewed, and eleven people with acquired visual impairment were questioned through an online questionnaire. Results: Among visually impaired people who enjoy leisure, almost half were helped by a third party. Some people thought that the occupational therapist could have a role to play in supporting leisure while others thought that it would not be relevant because it would require too many skills from the occupational therapist for him/her to perform his/her job properly. The interviewed occupational therapists, for their part, believed that they have an important role to play in this support. Conclusion: The occupational therapists based their care on the occupational balance of their patients and wished to support them more on this. However, leisure support is not in place yet and has limitations faced by occupational therapists. In addition, there is a request from visually impaired people to allow them access to leisure activities and if possible, with non-disabled people.Contexte : La déficience visuelle acquise survient au cours de la vie et résulte en une diminution importante de l’acuité visuelle d’un œil ou des deux yeux. Cette maladie nécessite un réapprentissage des gestes de la vie quotidienne et influe également sur l’accès aux loisirs. Le but de cette étude était d’explorer comment les personnes atteintes d’une déficience visuelle acquise accèdent à leurs loisirs et comment l’ergothérapeute peut les y accompagner.Méthode : Au travers d’une méthode qualitative, deux ergothérapeutes travaillant auprès d’une population déficiente visuelle ont été interviewées, et onze personnes atteintes d’une déficience visuelle acquise ont été interrogées via un questionnaire en ligne.Résultats : Parmi les personnes malvoyantes qui pratiquent des loisirs, un peu moins de la moitié se sont fait aider par une tierce personne. Une partie des personnes pense que l’ergothérapeute pourrait avoir un rôle à jouer dans l’accompagnement dans les loisirs alors que la seconde partie pense que ce ne serait pas pertinent car cela demanderait trop de compétences à l’ergothérapeute pour que celui-ci exerce correctement son métier. Les ergothérapeutes interrogées estiment, quant à elles, qu’elles ont un rôle important à jouer dans cet accompagnement.Conclusion : Les ergothérapeutes fondent leurs prises en charge sur l’équilibre occupationnel de leurs patients et souhaitent davantage les accompagner sur cet aspect-là. Cependant, l’accompagnement dans les loisirs n’est pas mis en place et présente des limites auxquelles les ergothérapeutes font face. Par ailleurs, une demande des personnes malvoyantes est présente afin de leur permettre un accès aux loisirs et si possible avec des personnes valides

Étude par microscopie en champ proche et diffraction d'électrons rapides des premiers stades de croissance de systèmes métalliques (application aux systèmes Fe/Cu(100), Cu/Fe(100) et Fe/Fe(100))

NANCY1-SCD Sciences & Techniques (545782101) / SudocSudocFranceF

New insight on competitive reactions during deep HDS of FCC gasoline

Dos Santos, N. Dulot, H. Marchal, N. Vrinat, M.In order to satisfy requests for high purity fuel, sulfur compounds have to be removed selectively from FCC gasoline with a minimum of olefins hydrogenation and recombination between olefins and H2S (product of hydrodesulfurization) to form thiols. Competition between hydrodesulfurization (HDS) and olefin hydrogenation (HYD) is truly a non-trivial subject. In this study, the impact of H2S on reactivity and selectivity has been studied for model compounds (3-methylthiophene and 1-hexene in heptame) under operating conditions allowing kinetic studies. Formation of C-6-thiols appears to be under thermodynamic control. Inhibition of H2S on both HDS and HYD reactions has been demonstrated. Moreover, inhibition of olefins on HDS and of 3MT on hydrogenation have been observed. This competition between HYD and HDS reactions is an argument in favor of an adsorption of both olefin and sulfur compounds on the same active sites. (C) 2008 Elsevier B.V. All rights reserved

Hydrotreatment modeling for a variety of VGO feedstocks : a continuous lumping approach.

International audienceThe Hydrotreatment of different VGO feedstocks in a pilot plant is modeled using the continuous lumping approach. A model with five continuous families (Parrafins, Naphtenes, sulfur-containing Aromatics, Nitrogen-containing Aromatics, and Sulfur and Nitrogen free aromatics) is proposed and validated in this work. The model considers the five families to be a continuous distribution. A reaction network, including hydrogenation, desulfurization, denitrogenization, and cracking is established and used to derive the kinetic rate expressions for each family. A total of 46 model parameters are adjusted, using data from 44 experimental runs, using a pilot plant. Three feedstocks of different origin and thus different characteristics (e.g. True Boiling Point, sulfur- and nitrogen content) were used in this this study. The same set of parameters was used to simulate hydrotreatment of all three feedstocks, which extends the range of applicability of the model beyond the models wich are typically proposed in literature, which rely on feedstock-specific parameters. The results show that this modeling approach is capable of accurately predicting the total hydrocarbon conversion and yield regardless of feed composition. Furthermore, insights into the underlying reaction mechanisms can be gained from the kinetic parameters