56 research outputs found
Development and Utilization of an E-learning Course on Heat Exchangers at ENSIC
No full textInternational audienceThis paper deals with the development and utilization of an e-learning course at ENSIC in France. Some definitions and examples of problem based learning (PBL) or e-learning utilizations in the world of chemical engineering are first given. This survey results from discussions held in the frame of the Working Party on Education of the European Federation of Chemical Engineering. The e-learning course developed at ENSIC is described and its use, according to an original pedagogy mixing e-learning and PBL, is detailed. The results show that this new pedagogy does not reduce the time of training but induces much more active learning, a better comprehension of technology and the possibility for the students to progress at their own rhythm. Author(s): E. Schaer 1, *, | C. Roizard 2, | N. Christmann 3, | A. Lemaitre
Photoinduced Electron Transfer as a Trigger for Molecular and Supramolecular Metamorphism
No full textInternational audienceThe key elements in the development of nanoscience are to observe, modify and control mater at the nanoscale. One strategy proposed to meet these immense challenges is to develop responsive molecular or supramolecular systems for which a structural reorganization is obtained when exposed to an external stimulus: this phenomenon is known as metamorphism. Systems that endure structural changes leading to major modification of macroscopic properties are of great interest for the controlled capture and release of guest molecules, the development of molecular machines and molecular electronics. The strategy developed at the Chemistry Laboratory of ENS Lyon is to exploit the switching and assembly properties of π-conjugated organic radicals that can be generated in-situ by electrical or light excitation.[1–3] This concept is based on molecular or supramolecular engineering strategies aiming at promoting the formation of -dimers in solution under usual conditions of temperature and concentration. A first approach consists in favoring the formation of π-dimers inside cavitands molecules such as cucurbituril in order to control the reversible association/dissociation of molecular building blocks into 2D-supramolecular assembly.[1] Another approach consists in connecting viologen subunits by labile coordination bond or with mobile covalent linker in order to guide and facilitate an electron-transfer triggered switching.[2,3] These strategies are very promising for the development of new soft-materials such as gels with switchable properties.[3–5]References[1] S. Chowdhury, Y. Nassar, L. Guy, D. Frath, F. Chevallier, E. Dumont, A. P. Ramos, G. J.-F. Demets, and C. Bucher, Electrochim. Acta, 316, 79–92 (2019).[2] C. Kahlfuss, S. Chowdhury, A. F. Carreira, R. Grüber, E. Dumont, D. Frath, F. Chevallier, Eric-Saint-Aman, and C. Bucher, Inorg. Chem., 60, 3543–3555 (2021).[3] C. Kahlfuss, T. Gibaud, S. Denis-Quanquin, S. Chowdhury, G. Royal, F. Chevallier, E. Saint-Aman, and C. Bucher, Chem. Eur. J., 24, 13009–13019 (2018).[4] S. Chowdhury, Q. Reynard-Feytis, C. Roizard, D. Frath, F. Chevallier, C. Bucher, and T. Gibaud, J. Phys. Chem. B, 125, 12063–12071 (2021).[5] C. Roizard, V. Andrieux, S. Al Shehimy, S. Chowdhury, Q. Reynard-Feytis, C. Kahlfuss, E. Saint-Aman, F. Chevallier, C. Bucher, T. Gibaud, and D. Frath, ECS Adv., 1, 020502 (2022)
Study of integration of the membrane separations in biomass gasification processes
No full textLa gazéification permet de convertir la biomasse en gaz de synthèse composé principalement d’H2, de CO et de CO2. Ce gaz peut être utilisé comme combustible dans des moteurs ou pour produire du gaz naturel de synthèse. En plus du syngaz, la gazéification génère des espèces aromatiques lourdes qualifiées de goudrons, comme le toluène, le naphtalène et le phénanthrène. Ces espèces posent divers problèmes pratiques. Elles nuisent aux catalyseurs de SNG (surtout le toluène car plus abondant). Pour un emploi en moteur, les problèmes viennent des goudrons lourds qui sont condensables. L’épuration du syngaz est donc nécessaire pour permettre son utilisation. La perméation de gaz dans une membrane polymère dense est une technologie employée pour diverses séparations. En particulier, les membranes en silicone (PDMS) sont plus perméables aux vapeurs organiques qu’aux gaz. Cette propriété est déjà utilisée à grande échelle pour retirer des vapeurs légères de flux d’air à température ambiante. La séparation envisagée dans cette thèse reprend cette idée mais avec des vapeurs inhabituellement lourdes et une température de 90°C, ce qui est élevé. La perméation repose sur des lois de sorption et de diffusion. Les paramètres de sorption ont été mesurés, ceux de diffusion ont été tirés de la littérature afin de permettre des simulations. Ces dernières révèlent que l’emploi d’une membrane en PDMS est une technologie prometteuse pour l’épuration du syngaz en vue d’un emploi en moteur. En revanche, cette technologie semble incapable de séparer efficacement le toluène des gaz permanents (par manque de sélectivité), ce qui la rend inapte à épurer le syngaz en vue d’une application de type SNG.Gasification allows to convert biomass into a synthesis gas containing mainly H2, CO and CO2. This gas can be used as a fuel in engines or to produce synthesis natural gas (SNG). In practice, heavy aromatic species named tars (such as toluene, naphthalene, phenanthrene) are generated along with syngas. These species generate various practical problems. They damage the SNG catalysts (especially toluene since it’s the most abundant). If syngas is used in a combustion engine, the problems are linked to the heaviest tars that can condense. Therefore, syngas upgrading is a key step to allow a good use. Gas permeation across a dense polymer membrane is a technology that is used for several separations. In particular, silicone membranes (PDMS) are more permeable to organic vapors than to permanent gases. This property is ever used at high scale to remove light vapors from fluxes of air or of nitrogen at ambient temperature. The separation that is considered in this study uses this idea but the vapors are heavy and the temperature is 90°C; that is, quite a high level of temperature. The permeation of species through a membrane is ruled by sorption and diffusion laws. The sorption parameters have been measured and the diffusion parameters have been obtained from literature in order to allow simulations. These simulations, show that the use of a PDMS membrane seems to be a promising technology to upgrade syngas for a use in an engine. On the other hand, this technology seems unable to efficiently separate toluene from permanent gases (because of a too low selectivity); that is, this technology is not able to upgrade syngas for use in SNG production
Potentials of pervaporation to assist VOCs' recovery by liquid absorption
No full textInternational audienceGas treatment by liquid absorption is a well-known process to remove volatile organic compounds (VOCs) from industrial waste gases. Usually the liquid is an organic solvent of high boiling point; however, after VOCs' absorption it must be regenerated for the possible reuse and this step is classically achieved by heating the liquid. The paper presents the work directed to investigate an alternative regeneration step based on a liquid–vapour membrane separation, i.e. pervaporation. Because most of the energy required in pervaporation processes is consumed to remove the minor component from the initial mixture by selective permeation through the membrane, one can expect a significant energy cut in the operational costs linked to the regeneration of the liquid if the pervaporation step can substitute the heating one. The results reported here show that the technological possibility to use pervaporation is first governed by the stability of the membrane in the absorption liquid. The viability of the overall process is actually controlled by the mutual affinity between the VOCs, the solvent phase and the polymeric material. As a matter of fact, whereas VOCs have to exhibit strong affinities to both the solvent and the membrane material, the polymer has to be well resistant and even repellent to the solvent to avoid the possible sorption in the membrane that would drastically depress the pervaporation efficiency. In other words the membrane transport properties must be specific for the VOCs. This goal was reached following several experimental approaches, going from membrane modifications to the selection of suitable heavy protic solvents. Hence it has been shown for the case of dichloromethane (DCM) that low molecular weights polyalcohols (e.g. glycols) appeared to be suitable media to allow in particular the specific transport of DCM. On the other hand, polydimethylsiloxane (PDMS) based membranes were selected for their stability in these polyglycols and for their marked affinity for DCM. The simulation of the hybrid gas treatment process at pilot-scale was also achieved by a simple model relying on experimental data for both vapour liquid equilibria and permeation flux. A simple comparison of the energy needed to regenerate the heavy solvent by each possible step has also been made
Preparation and evaluation of Asymmetric co-Polyetherimide Membranes (PEI) for the separation of organic compounds from water
No full textLe mémoire rapporte les travaux effectués pour l’élaboration de membranes asymétriques de type co-polyalcoxyéther-imide (PEI) afin d'obtenir des membranes polymères à haut flux, sélectives pour la séparation de molécules organiques à partir de mélanges aqueux par procédés membranaires. La séparation des mélanges liquides (i.e. toluène - heptane, eau - éthanol, soluté organique dilué en solution aqueuse) a été étudiée par pervaporation (PV) et par nanofiltration (NF) à l'aide de membranes PEI originales asymétriques comportant une peau dense autosupportée. Ces membranes ont été préparées dans des conditions expérimentales contrôlées à partir de solutions DMF-H2O de l'acide polyamique correspondant (APA) en relation avec le diagramme de phase ternaire ; après l’inversion de phase dans un bain d'eau, les membranes d’APA ont été cyclisées en imides par traitement thermique. Les propriétés physiques des membranes (IR, TGA) ont été caractérisées, et les morphologies correspondantes, enregistrées par SEM, ont été utilisées pour optimiser la préparation des membranes asymétriques pour améliorer les propriétés de séparation en ajustant l'épaisseur de la couche dense. Les performances obtenues en pervaporation et en nanofiltration ont été examinées à la lumière de l'influence de trois séries de paramètres, à savoir les paramètres d’élaboration des membranes (composition du collodion, température du bain d'inversion de phase), les conditions expérimentales de perméation (température, pression) et des propriétés moléculaires du soluté (masse molaire, rayon, polarité). Les résultats de pervaporation ont montré que des membranes asymétriques PEI à peau denses pouvaient bien être obtenues, donnant lieu à une sélectivité moléculaire en accord avec le modèle de solution-diffusion. Les résultats obtenus en NF pour des solutés organiques dilués dans l'eau (≈ 500 ppm) ont montré que le degré de rejet des solutés étaient fortement liés aux conditions d’élaboration des membranes PEI et des propriétés des solutés. Les valeurs de seuil de coupure moléculaire des membranes (MWCO) ont été déterminées avec une série de polyéthylène glycol (400 <MW (g/mole) < 6000) pour une pression appliquée allant jusqu'à 10 bar. Il a été montré que le seuil de coupure des membranes était compris entre 400 et 1000g/mol à 30°C. Il a également été constaté pour certaines membranes PEI que de grandes valeurs de flux de perméation associées à de bonnes sélectivités pouvaient être obtenues, conduisant à des performances intéressantes par rapport aux données de la littérature. Ainsi le développement de ces nouvelles membranes asymétriques copolyimides comprenant un bloc élastomère devrait permettre d’obtenir des membranes de hautes performances pour des applications dans les séparations liquide-liquide, en particulier pour les séparations de nanofiltration en milieu aqueuxThe work aimed to prepare co-polyalkylether-imide (PEI) asymmetric membranes in order to get high flux water selective polymeric membranes suitable for the separation of organic molecules from aqueous mixtures by membrane processes. The separation of liquid mixtures (i.e. toluene – heptane, water – ethanol and low concentrated organic solute in aqueous solutions) was studied by pervaporation (PV) and by nanofiltration (NF) using homemade integrally skinned asymmetric PEI membranes. These membranes were prepared under controlled experimental conditions from DMF-H2O solutions of the corresponding polyamic acid (PAA) with respect to the ternary phase diagram; after the wet phase inversion in a water bath, the PAA membranes were imidized by thermal treatment. The membrane physical properties (IR, TGA) were characterized and the related morphologies, recorded by SEM, were used to optimize the asymmetric membrane preparation to improve the separation properties by tuning the thickness of the dense top layer. The performances of the pervaporation and nanofiltration separations were examined in the light of the influence of three sets of parameters, i.e. membrane elaboration parameters (dope composition, inversion bath temperature), experimental permeation conditions (temperature, applied pressure) and solute molecular properties (molecular weight, radius, polarity). The PV results showed that tight asymmetric PEI membranes could well be obtained, giving rise to a molecular selectivity in agreement with the solution-diffusion model. The NF results obtained with diluted organics in water (≈500ppm) have shown that the degree of rejection of the organic solutes was strongly linked to the PEI elaboration conditions and to the solute properties. The molecular cutoff values (MWCO) of the membranes were determined with a series of polyethyleneglycol (400 < Mw (g/mole) <6000) for an applied NF pressure up to 10 Bar; it was shown that the PEI membrane MWCO could be ranged between 400 and 1000g/mol at 30°C. It was also found with some PEI membranes that high permeation fluxes together with good separation selectivity could be obtained leading to interesting performances compared to literature data. Thus, it is expected that the development of these new asymmetric block copolyimide rubbery membranes might give rise to high performance membrane systems for applications in liquid-liquid separations, in particular in nanofiltration separation
REMOVED: CO2 Selective Membrane Materials on the Basis of Poly(Vinyltrimethylsilane)-graft-poly(Ethylene Glycol)
No full textThis article has been removed: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).This article has been removed at the request of the Executive Publisher.This article has been removed because it was published without the permission of the author(s)
Study of polymer-carbon mixed matrix membranes for CO2 separation from flue gas
No full textInternational audienceThere is a great concern about green house gases (GHG) impact on the global climate mitigation and numerous studies aim at the reduction of GHG emissions. Among targeted gases (VOC, CH4), carbon dioxide remains actually the main objective because its emission is strongly associated with the industrial development and with the energy production from fossil sources which, up to now, cannot be quickly substituted by any other sources except by nuclear energy. If they are many types of stream containing CO2, one can easily classify them into two main categories according to their pressure and temperature ranges that can be either high (P > 50 bar, t° > 200°C) or low (P < 2 bar, t° < 150°C); generally speaking these cases are known as pre-combustion or post-combustion. The work reported in this study is dedicated to the postcombustion case and polymer based membranes able to improve CO2/N2 capture from flue gas were studied from readily available glassy polymers
Photo/Redox-responsive Supramolecular Materials Based on Viologens
No full textInternational audienceThe incorporation of photo/redox-active units based on N,N'-disubstituted 4,4'-bispyridinium salts, commonly known as viologens, in the structure of supramolecular assemblies has been shown to confer interesting electron-accepting and photo/electrochromic properties to the materials. These responsive units have already been used as key elements for the development of electrochromic devices, molecular machines and organic batteries. Our research efforts in this field have led us to focus on molecular and supramolecular architectures involving viologens as key electron-responsive building elements. [1] In particular, we have developed different strategies allowing to exploit the ability of viologen derivatives to form π-dimers in their reduced state to achieve a remote control over their organization within supramolecular assemblies. Among our recent achievements, we have reported a sol/gel transition triggered by light-irradiation of a viologen-based coordination polymer formed in the presence of palladium ions. [2] We now report supramolecular gels obtained by selfassembly of a dicationic low molecular weight gelator based on viologen. These molecules have been shown to self-assemble in pentanol to form chiral hollow coreshell cylinders eventually yielding dendritic clusters inducing gelation. We also showed that the optical, rheological and electrical properties of the gels can be tuned by addition of ionic additives. Careful control of the formation of charge-transfer complexes between viologens and iodides have led to a robust, transparent, conductive and chiral gel. [3] Properties of this responsive material can be modulated when submitting it to electrical or light stimulation. [1] (a) S. Chowdhury, Y. Nassar, L. Guy, D. Frath, F. Chevallier, E. Dumont, A. P. Ramos, G. Demets, C. Bucher, Electrochim. Acta 2019, 316, 79–92. (b) S. Al Shehimy, O. Baydoun, S. Denis-Quanquin, J.-C. Mulatier, L. Khrouz, D. Frath, E. Dumont, M. Murugesu, F. Chevallier and C. Bucher, J. Am. Chem. Soc. 2022, 144, 17955–17965. [2] (a) S. Chowdhury, Q. Reynard-Feytis, C. Roizard, D. Frath, F. Chevallier, C. Bucher, T. Gibaud, J. Phys. Chem. B 2021, 125, 12063–12071. (b) C. Roizard, V. Andrieux, S. Al Shehimy, S. Chowdhury, Q. Reynard-Feytis, C. Kahlfuss, E. Saint-Aman, F. Chevallier, C. Bucher, T. Gibaud, D. Frath, ECS Adv. 2022, 1, 020502.[3] V. Andrieux, T. Gibaud, J. Bauland, T. Divoux, S. Manneville, S. Guy, A. Bensalah-Ledoux, L. Guy, F. Chevallier, D. Frath, C. Bucher, J. Mater. Chem. C 2023, 11, 12764–12775
Industrial photochemistry XV: Interests and limits of the buckingham theorem for the design of industrial photoreactors
No full textPossibilities and Limitations of Pervaporation for Improved Acetic Acid Dehydration by Distillation at Industrial Scale: A Critical Analysis
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