Preparative fractionation of a random copolymer (SAN) with respect to either chain length or chemical composition

The possibilities to fractionate copolymers with respect to their chemical composition on a preparative scale by means of the establishment of liquid/liquid phase equilibria were studied for random copolymers of styrene and acrylonitrile (san). Experiments with solutions of san in toluene have shown that fractionation does in this quasi-binary system, where demixing results from marginal solvent quality, take place with respect to the chain length of the polymer only. On the other hand, if phase separation is induced by a second, chemically different polymer one can find conditions under which fractionation with respect to composition becomes dominant. This opportunity is documented for the quasi-ternary system dmac/san/polystyrene, where the solvent dimethyl acetamide is completely miscible with both polymers. The theoretical reasons for the different fractionation mechanisms are discussed

Intérêt d'un modèle agrégé pour étudier le comportement et simplifier la simulation d'un modèle individu-centré de consommation couplé à un modèle de ressource en eau

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Gasphasen-Synthese von Dimethylcarbonat durch katalytische oxidative Carbonylierung von Methanol: Entwicklung einer chloridfreien Verfahrensvariante mit neuartigen Katalysatoren unter Nutzung kombinatorischer Prinzipien : Forschungsprogramm WING (Werkstoffinnovation für Industrie und Gesellschaft) ; Abschlussbericht ; (Laufzeit des Vorhabens 1.1.2004 - 31.12.2005)

[no abstract available

Decomposition of methane over alumina supported Fe and Ni–Fe bimetallic catalyst: Effect of preparation procedure and calcination temperature

AbstractCatalytic decomposition of methane has been studied extensively as the production of hydrogen and formation of carbon nanotube is proven crucial from the scientific and technological point of view. In that context, variation of catalyst preparation procedure, calcination temperature and use of promoters could significantly alter the methane conversion, hydrogen yield and morphology of carbon nanotubes formed after the reaction. In this work, Ni promoted and unpromoted Fe/Al2O3 catalysts have been prepared by impregnation, sol–gel and co-precipitation method with calcination at two different temperatures. The catalysts were characterized by X-ray diffraction (XRD), N2 physisorption, temperature programmed reduction (TPR) and thermogravimetric analysis (TGA) techniques. The catalytic activity was tested for methane decomposition reaction. The catalytic activity was high when calcined at 500°C temperature irrespective of the preparation method. However while calcined at high temperature the catalyst prepared by impregnation method showed a high activity. It is found from XRD and TPR characterization that disordered iron oxides supported on alumina play an important role for dissociative chemisorptions of methane generating molecular hydrogen. The transmission electron microscope technique results of the spent catalysts showed the formation of carbon nanotube which is having length of 32–34nm. The Fe nanoparticles are present on the tip of the carbon nanotube and nanotube grows by contraction–elongation mechanism. Among three different methodologies impregnation method was more effective to generate adequate active sites in the catalyst surface. The Ni promotion enhances the reducibility of Fe/Al2O3 oxides showing a higher catalytic activity. The catalyst is stable up to six hours on stream as observed in the activity results

Decomposition of methane over alumina supported Fe and Ni–Fe bimetallic catalyst: Effect of preparation procedure and calcination temperature

Catalytic decomposition of methane has been studied extensively as the production of hydrogen and formation of carbon nanotube is proven crucial from the scientific and technological point of view. In that context, variation of catalyst preparation procedure, calcination temperature and use of promoters could significantly alter the methane conversion, hydrogen yield and morphology of carbon nanotubes formed after the reaction. In this work, Ni promoted and unpromoted Fe/Al2O3 catalysts have been prepared by impregnation, sol–gel and co-precipitation method with calcination at two different temperatures. The catalysts were characterized by X-ray diffraction (XRD), N2 physisorption, temperature programmed reduction (TPR) and thermogravimetric analysis (TGA) techniques. The catalytic activity was tested for methane decomposition reaction. The catalytic activity was high when calcined at 500 °C temperature irrespective of the preparation method. However while calcined at high temperature the catalyst prepared by impregnation method showed a high activity. It is found from XRD and TPR characterization that disordered iron oxides supported on alumina play an important role for dissociative chemisorptions of methane generating molecular hydrogen. The transmission electron microscope technique results of the spent catalysts showed the formation of carbon nanotube which is having length of 32–34 nm. The Fe nanoparticles are present on the tip of the carbon nanotube and nanotube grows by contraction–elongation mechanism. Among three different methodologies impregnation method was more effective to generate adequate active sites in the catalyst surface. The Ni promotion enhances the reducibility of Fe/Al2O3 oxides showing a higher catalytic activity. The catalyst is stable up to six hours on stream as observed in the activity results

Simultaneous quick-scanning X-ray absorption spectroscopy and X-ray diffraction

The existing setup for time-resolved quick-scanning X-ray absorption spectroscopy (QEXAFS) at beamline P64 at the PETRA III storage ring is complemented by new infrastructure suited for the collection of X-ray diffraction data simultaneously to the QEXAFS experiment. In particular, the sinusoidal periodic movements of the quick-EXAFS mono-chromator are modified in such a way, that an energy plateau with approximately constant energy over a certain time is created in the pre-edge region of the absorption edge of interest. By employing a properly defined trigger signal in this time, the exposure of a two-dimensional X-ray detector placed behind the sample is actuated, thus allowing to collect an X-ray diffraction pattern over a certain angular range as defined by the actual X-ray energy and the position of the 2D-detector. Details of the new setup as well as exemplary results obtained during the solvothermal synthesis of ZnO nanoparticles and the bcc-fcc phase transition of iron at elevated temperatures are presented