172,776 research outputs found
Vanadia Promoted Co-AI20 3 Fischer-Tropsch Catalysts
No full textBibliography: leaves 117-124.The primary aim of this work was to study systematically V20 5 promotion on yAI203 supported cobalt-based Fischer-Tropsch catalysts. The y-Ah03 support was modified by addition of varying amounts of vanadia and was subsequently loaded with the same Co content (10 wt-%). The modified supports and catalysts were characterised using conventional characterisation methods. The physio-chemical properties of the vanadia promoted supports and catalysts were characterised using Atomic Adsorption Spectroscopy (AAS), zeta-potential measurements, and BET measurements, X-ray Diffraction (XRD), Temperature Programmed Reduction (TPR), Transmission Electron Microscopy (TEM), and CO chemisorption. Catalyst performance in the Fischer-Tropsch synthesis was tested in fixed bed reactor. A catalysts synthesised from plain y-A1203 was used as a base catalyst. Characterization results show that modification of y-Ab03 support to obtain V205 loadings beyond 1-monolayer vanadia coverage was difficult when using ion exchange. Ion-exchange equilibrium limitations might have caused the poor vanadia loadings beyond 1-monolayer coverage. The supports net surface charge as measured using zeta potential, was decreased by vanadia content in the supports. CO chemisorption results were complex and could only be modelled using dual site Langmuir model assuming the presence of two different sites absorbing CO on the Co-V-AI catalyst system. This made extraction of physical properties from this method rather difficult. Fischer Tropsch synthesis reaction was carried out at typical industrial conditions (T=220°C, P=20 bar (a), H2/CO=2 Xco-60 mol-%) for cobalt catalysts. Vanadia promoted catalysts showed a marked decrease in initial activity. However, the overall deactivation rate was lower with increasing vanadia content. The vanadia content did not affect the chain growth kinetic behavior of the catalyst in the Fischer-Tropsch synthesis hence C5+ selectivity in the Fischer-Tropsch synthesis was unperturbed by vanadia content. Increasing the vanadia content in the catalyst resulted in high n-olefin content and high 1-olefin content. The observed increase in olefin content might be due to the low catalytic activity observed for the catalysts with high vanadia loadings. The most pronounced effect of vanadia promotion on Fischer Tropsch synthesis was in the oxygenate content in the Fischer-Tropsch product. Catalysts with high vanadia loading yielded high amounts of oxygenate products; mainly alcohols and aldehydes
Modeling Fischer Tropsch synthesis in two-phase, continuous, well-mixed slurry reactors
No full textIncludes abstract.Includes bibliographical references (p. 84-87).Fischer Tropsch Synthesis (FTS) is the conversion of syngas (CO and H2) to cleaner liquid transportation fuels. The modelling of such a supercritical, highly non-ideal, multi-component system requires the detailed knowledge of the reaction mechanism, reaction kinetics, phase-equilibrium and reactor technology. The objectives of this work were to: develop a complete Fischer Tropsch model, predict the hydrocarbon product distribution, determine what effect Vapour-Liquid Equilibrium (VLE) has on the product distribution, selectivity and kinetics, and determine whether the deviations from the 'ideal' Anderson-Schulz Flory (ASF) distribution can be attributed to VLE
Supplementary data and results of the application of a proposed approach of the characteristic equation method in a thermodynamic simulation for different single-effect lithium bromide/water (LiBr/H2O) absorption chillers
No full textA proposed approach of the characteristic equation method presented in a previous study (Fischer et al., 2020) was thermodynamically simulated for six different LiBr/H2O single-effect absorption chillers in a more recent study.The input data of the internal parameters of each absorption chiller, which are all the overall heat transfer conductances (UA) and the internal mass flow rate of the weak solution of the absorption chiller were collected in the literature (Boudehenn et al., 2014; Fischer et al., 2020; Martínez et al., 2016; Herold et al., 2016; Gommed and Grossman, 1990) The input data of the temperatures and mass flow rates of the external water circuits were selected from the usual nominal temperature ranges were found in the literature.Figure 1 presents the single-effect lithium bromide/water (LiBr/H2O) absorption chiller with its components and temperature points numbered. The numbers in this figure correspond to the chiller points in the study as well.The values of the input data of the internal parameters of each absorption chiller are shown in Table 1.The chiller Tables present the values of the input data of the temperatures of the external water circuits and the main results of the simulation.The figures of the graphs present the distribution of the points of the results of the simulation.References: Fischer, Y., Dutra, J. C. C., Rohatgi, J. (2020): Thermodynamic modelling of a LiBr-H2O absorption chiller by improvement of characteristic equation method. International Journal of Refrigeration, vol. 120, pp. 420-429.Boudéhenn, F., Bonnot, S., Demasled, H., Lazrak, A. (2014): Comparison of different modeling methods for a single effect water-lithium bromide absorption chiller. Proceedings of the International Conference on Solar Energy and Buildings, Aix-les-Bains, France.Martínez, J. C., Martinez, P. J., Bujedo, L. A. (2016): Development and experimental validation of a simulation model to reproduce the performance of a 17.6 kW LiBr-water absorption chiller. Renewable Energy, vol 88, pp. 473-482Herold, K. E., Radermacher, R. Klein, S. A. (2016): Absorption chiller and heat pumps. CRC Press, New York, 2nd ed.Gommed, K., Grossman, G. (1990): Performance analysis of staged absorption heat pumps: water-lithium bromide systems. Ashrae Transactions, vol. 96, part 1
The effect of temperature on the Fischer-Tropsch selectivity and further mechanistic insights
No full textIncludes bibliographical references (p. 133-145).Concern’s that the world’s energy supply will not be able to keep pace with rising energy demands, have surfaced periodically for much of the petrochemical industry’s nearly 150 year history, but each time the industry has responded with technological advances and innovations to satisfy the global energy needs. Future advances will most likely include the enhanced recovery of conventional oil, the production of extra-heavy oil / tar sands and the utilization of alternative energy production technologies (technologies other than crude oil refining). The Fischer-Tropsch Synthesis (FTS) discovered in 1923 by Fischer and Tropsch, is one of these alternative fuel production technologies and can briefly be defined as the means used to convert synthesis gas containing hydrogen and carbon monoxide over a group VIII metal catalyst to hydrocarbon products and water. Given the vast product spectrum possible for the FTS (paraffins, olefins, alcohols, carbonyls, acids and aromatics), a great deal of controversy still exists as to the chemical identity of the monomeric building block and the propagation of the hydrocarbon chain on the catalyst surface [van Dijk., 2001]. Several mechanisms have been published with the four most popular (alkyl, alkenyl, enol and CO-insertion), recently reviewed by Claeys and van Steen (2004). It must however, be appreciated that given the complexity of the FT reaction it is generally accepted that more than one mechanism may operate on the catalyst surface at any one time. Furthermore, process parameters such as temperature, total pressure, partial pressure, hydrogen to carbon monoxide ratio, space velocity and residence time all have an influence on the FT product selectivity. Because of this it becomes exceptionally complicated to determine the effects of just one parameter while taking the effects of the additional parameters into account
Verifying concurrent programs by memory unwinding
No full textWe describe a new sequentialization-based approach to the symbolic verification of multi-threaded programs with shared memory and dynamic thread creation. Its main novelty is the idea of memory unwinding, i.e., an explicit representation of the sequence of write operations into the shared memory. For the verification, we nondeterministically guess this unwinding and then simulate the behavior of the program according to any scheduling that respects this guess. This approach is complementary to other sequentializations and explores an orthogonal dimension, i.e., the number of write operations. It also simplifies the implementation of several important optimizations, in particular the targeted exposure of individual writes. We implemented this approach as code-to-code transformation from multi-threaded into nondeterministic sequential programs, which allows the reuse of sequential verification tools. Experiments show that our approach is very promising: it found all errors in the concurrency category of SV-COMP15
Influence of basicity in Fischer-Tropsch synthesis over supported iron-based catalysts
No full textIncludes bibliographical references (leaves 115-124).The Fischer-Tropsch synthesis catalyzed by iron is a well-established process for the production of synthetic fuels, waxes and high-value chemicals, such as α-olefins. A draw-back of the currently used iron-based catalysts is their short lifetime, caused by sintering and particle break-up. These disadvantages might be overcome by utilizing a supported iron-based catalyst. However, supported iron Fischer-Tropsch synthesis, which has been tested up to now, show a high methane selectivity. This might be caused by a lack of alkali near the catalytic site, which can be alleviated by using a basic support. Classical basic supports such as CaO and MgO will react with CO2 (a major by-product in iron-catalyzed Fischer-Tropsch synthesis) yielding carbonates and can therefore not be used, since the formation of carbonates will result in a large particle expansion. An alternative would be to generate a silica-based basic support by attaching basic groups to the silica. In this study iron Fischer-Tropsch catalysts supported on silica were tested for conversion of synthesis gas to hydrocarbon products. Silica was modified with aminopropyltriethoxysilane (APTeS) by impregnation followed by calcination to provide basic surface groups onto the silica surface. The CHN analysis and IR-analysis indicate the presence of amine groups in the APTeS-modified silica. The pore radius distribution of silica is slightly shifted towards higher pore radii in comparison to APTeS-modified silica. It might thus be stated that aminopropyltriethoxysilane covers the pore walls and does not seem to result in pore blockage. Thermal gravimetric analysis indicates that the thermal stability of APTeS-modified silica is low. A major difference between silica and APTeS-modified silica was their zeta-potential. Whereas the surface of silica is mainly negatively charged in the pH-range of interest during impregnation, the surface of APTeS-modified silica is mainly positively charged. This is attributed to the presence of amine groups on the surface. Iron was brought onto the support by impregnation. The surface modification of silica with APTeS seems to be destroyed upon calcination of the impregnated catalysts. The iron phase in the calcined iron catalyst supported on silica catalysts is mainly hematite (Fe203), whereas the iron phase in the calcined iron catalyst supported on APTeS-modified silica catalysts is mainly iron oxide hydroxide FeOOH. The presence of basic amine groups may favour the formation of FeOOH crystallites during the impregnation/calcination on the APTeS-modified silica. The FeOOH-crystallites on the APTeS-modified silica support are typically smaller than the Fe203 crystallites on silica. The maximum catalytic activity is obtained at 0.01 mol K I mol Fe for the iron catalyst supported on silica and at 0.02 mol K I mol Fe for the APTeS-modified catalyst, indicating the optimum potassium loading. The difference in the optimum potassium loading might be linked to the smaller crystallite sizes obtained with the APTeS-modified catalyst. All the potassium promoted catalysts show a lower methane selectivity compared to the 0 K iron catalyst supported on silica and the 0 K iron catalyst supported on APTeS-modified silica. The 1-olefin and n-olefin content in the fraction of linear hydrocarbons increase with increasing potassium loading over all the iron catalyst supported on silica promoted with potassium except for the catalysts 0.005 K and 0.01 K. Increasing potassium content on the catalyst resulted in higher 1-olefin content in the fraction of linear olefins. The trend suggests that potassium promotion suppresses secondary double bond isomerisation of 1-0lefin into internal olefins. The high degree of branching obtained with the 0.005 K catalyst and the 0.01 K catalyst, is characteristic of weak alkali promotion. The iron catalysts supported on APTeS-modified silica indicate an increase in the degree of branching with increasing potassium content
Reseña del libro “De vínculos, subjetividades y malestares contemporáneos”
No full textFil.: Fischer, Ileana Veronica (s.af.)Este libro es una obra colectiva conformada por psicoanalistas argentinos que provienen de diversos campos del psicoanálisis que se dispusieron a poner en diálogo esa diversidad para establecer cruces, confrontaciones y enriquecimientos respecto de los tintes de época que caracterizan los modos de producción de las subjetividades y los malestares y sufrimientos que se ponen de manifiesto
A smoothing Newton method based on the generalized Fischer-Burmeister function for MCPs
No full text[[abstract]]We present a smooth approximation for the generalized Fischer-Burmeister function where the 2-norm in the FB function is relaxed to a general p-norm (p > 1), and
establish some favorable properties for it, for example, the Jacobian consistency. With the smoothing function, we transform the mixed complementarity problem (MCP) into
solving a sequence of smooth system of equations.
Emilio Fischer
No full textEn Euskirchen, cerca de Colonia y de Bonn, nació el 9 de octubre de 1852 Emilio Fischer. Su padre, Laurenz Fischer, procedía de una vieja familia protestante de la comarca. Emilio fue el hijo menor y único varón. Cursó estudios primero en Wetzlar y más tarde estudios secundarios en Bonn, y en la misma ciudad, después de un breve ensayo comercial, comenzó a estudiar química.Ha contado Fischer, en sus memorias, como su padre insistió que eligiera química, en lugar de matemática y física que él deseaba. Le parecían demasiados abstractas, de pocas posibilidades materiales. Alar mado por el fracaso de su hijo como hombre de negocios, decía «El joven Emilio es demasiado tonto para comerciante, tiene que estudiar«. (...)En Euskirchen, cerca de Colonia y de Bonn, nació el 9 de octubre de 1852 Emilio Fischer. Su padre, Laurenz Fischer, procedía de una vieja familia protestante de la comarca. Emilio fue el hijo menor y único varón. Cursó estudios primero en Wetzlar y más tarde estudios secundarios en Bonn, y en la misma ciudad, después de un breve ensayo comercial, comenzó a estudiar química.Ha contado Fischer, en sus memorias, como su padre insistió que eligiera química, en lugar de matemática y física que él deseaba. Le parecían demasiados abstractas, de pocas posibilidades materiales. Alar mado por el fracaso de su hijo como hombre de negocios, decía «El joven Emilio es demasiado tonto para comerciante, tiene que estudiar«. (...
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