14,294 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
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
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
Investigation of the promotional effect of Cu and Ag on iron-based Fischer-Tropsch catalysts using ferrites as model catalysts
No full textIncludes bibliographical references.The Fischer-Tropsch synthesis is regarded as a stepwise polymerisation reaction between adsorbed hydrogen, carbon monoxide and monomers formed from the reaction of hydrogen and carbon monoxide. The catalytically active metals for industrial application are cobalt and iron. The commercially used iron-based Fischer-Tropsch catalyst is supported on silica (Si), to improve the dispersion of the active metal and is promoted with small amounts of potassium to enhance the activity and selectivity of the catalyst and copper to enhance the reducibility of the iron oxide. However, the effect of copper on the iron catalyst on the product activity and selectivity remains elusive. A number of studies that have been conducted on the promotional effect of copper on iron-based Fischer-Tropsch catalysts have mainly been focused on fully promoted iron-based FT catalyst (Fe/Cu/K/Si), thus making it difficult to exclusively study the effect of the overall promotional effect of copper on the FT performance of iron-based catalysts. Additionally, minimal work has been conducted on the promotional effect of metals (i.e. silver) in the same group in the periodic table as copper. A previous study further showed that silver had no effect on the FT performance of the iron catalysts. These results were ascribed to the lack of intimate contact between the promoter and the catalytically active phase. In this study, copper and silver ferrites which are model iron catalysts composed of Cu or Ag as promoters (CuFe2O4, CuFeO2 and AgFeO2) will be prepared via the co-precipitation method. The model catalysts will then be activated in H2 and CO reaction environment and exposured to Fischer-Tropsch conditions in an attempt to understand the influence of the copper (Cu) as well as silver (Ag) on the iron catalyst. The results are compared to maghemite (γ-Fe2O3) and hematite (α-Fe2O3). The presence of group 11 metals in the crystal structure facilitates the reduction of trivalent iron into magnetite during catalyst activation in either hydrogen or carbon monoxide and the consecutive conversion of Fe3O4 to α-Fe under H2-activation implying the ability of these metals to spillover hydrogen to Fe3O4. The conversion of Fe3O4 to predominantly χ-Fe5C2 under CO-treatment is not facilitated by the presence of the promoter element. The amount of carbide in the catalyst under Fischer–Tropsch conditions is dependent on the presence of the promoter (Cu and Ag) in close proximity to the iron phases. An increase in the FT activity is observed for the promoted iron catalysts, and this is primarily attributed to the increased carbide surface area within the catalyst. Carbon dioxide (CO2) in the Fischer-Tropsch synthesis is formed either in the oxygen removal from the catalytic surface or in the carburization of particularly superparamagnetic Fe3O4. It is further shown that the olefin selectivity in the Fischer-Tropsch synthesis over the catalyst AgFeO2 (ex) is higher than that obtained over the catalyst CuFe2O4 (ex) and CuFeO2 (ex), which can be ascribed to a lower hydrogenation activity of silver in comparison to copper ((ex) is in reference to the model catalyst after Fischer-Tropsch synthesis). Furthermore, copper seems to facilitate secondary olefin hydrogenation
Carbidization and size effects of unsupported nanosized iron in the low temperature Fischer-Tropsch process
No full textIncludes abstract.Includes bibliographical references.In the process of developing the most efficient production of fuels from coal or natural gas, there have been major advances in the development of the catalysts used. Previous work at the Centre for Catalysis Research, at the University of Cape Town, has shown great potential and provided a much deeper under- standing of the workings of the Fischer-Tropsch catalyst. The research has found that the catalyst crystallite size plays a crucial part in the product selectivity and requires strict control in order to obtain a certain desired product spectrum. The aim of this project is to provide insight on the behavior of various iron oxide crystallite sizes when placed in a CO concentrated environment during catalyst pretreatment. It will also clarify whether the sizes of the nano-crystallites will increase or decrease when the different phases form and which size carbides faster
Anne Fischer Collection. 1884-1982 bulk: 1930-1978
No full textThis collection contains the correspondence and personal papers of Anne Fischer. The bulk of the material consists of nearly five decades of continuous correspondence between Anne Fischer and Hermann Simon. In addition, there is a very small amount of official documents of family members and a few photographs.Anne Fischer was born on August 12, 1902 in Stuttgart. She was the daughter of the physician Bernard Rosenberg and his wife Hedwig Rosenberg née Lerchenthal, and she had an older brother, Eric. Anne Fischer married the physician Ernst Fischer, and they had two children: George and Eva. Anne Fischer went to the United States with her children in August 1934, following her husband who had immigrated earlier. The family first settled in Rochester before moving to Richmond, Virginia. She returned to Germany several times following World War II.Photographs removed to Photograph Collectiondigitize
Caulobacter crescentus adapts to phosphate starvation by synthesizing anionic glycoglycerolipids and a novel glycosphingolipid
No full textCaulobacter crescentus adapts to phosphate starvation by elongating its cell body and a polar stalk structure. The stalk is an extension of the Gram-negative envelope containing inner and outer membranes as well as a peptidoglycan cell wall. Cellular elongation requires a 6- to 7-fold increase in membrane synthesis, yet phosphate limitation would preclude the incorporation of additional phospholipids. In the place of phospholipids, C. crescentus can synthesize several glycolipid species, including a novel glycosphingolipid (GSL-2). While glycosphingolipids are ubiquitous in eukaryotes, the presence of GSL-2 in C. crescentus is surprising since GSLs had previously been found only in Sphingomonas species, in which they play a role in outer membrane integrity. In this paper, we identify three proteins required for GSL-2 synthesis: CcbF catalyzes the first step in ceramide synthesis, while Sgt1 and Sgt2 sequentially glycosylate ceramides to produce GSL-2. Unlike in Sphingomonas, GSLs are nonessential in C. crescentus; however, the presence of ceramides does contribute to phage resistance and susceptibility to the cationic antimicrobial peptide polymyxin B. The identification of a novel lipid species specifically produced upon phosphate starvation suggests that bacteria may be able to synthesize a wider variety of lipids in response to stresses than previously observed. Uncovering these lipids and their functional relevance will provide greater insight into microbial physiology and environmental adaptation.Peer reviewe
Waste to fuels via the Fischer-Tropsch process:A modularized approach
No full textWaste-to-fuel technology is becoming increasingly important in the global sustainability landscape. Despite this, the commercialization of the waste-to-liquid process via the Fischer-Tropsch synthesis (a widely used technique to convert organic matter to fuels) has been slower than anticipated. This is due to the complex economics behind the Fischer-Tropsch process: high capital costs combined with the decentralized nature of waste decreases viability based on economies of scale. Designing the Fischer-Tropsch process in a simpler, modularised manner may increase the economic viability of these types of processes. This chapter will introduce the concept of waste-to-fuel technology and give a context for the Fischer-Tropsch synthesis within this paradigm. Following this is a discussion on the 21st century commercialization of Fischer-Tropsch waste-to-fuel technology and the complex economics that have led to the delay in widespread commercialization. Finally, this chapter will provide some key design strategies that can be incorporated into the Fischer-Tropsch process, making it more suitable for decentralized waste-based applications
Preparation of nano and Angstrom sized cobalt ensembles and their performance in the Fischer-Tropsch synthesis
No full textIncludes bibliographical references.In Fischer-Tropsch synthesis carbon monoxide and hydrogen are converted in a surface polymerisation reaction over a heterogeneous catalyst to mainly long chain hydrocarbons and water. Although all group VIII metals are reported to show activity in this process, only iron and cobalt are used on an industrial scale due to availability and costs. In order to minimise the costs of these catalysts it is generally important to increase the mass specific active surface area by dispersing the active material on an inert carrier. Recent studies on nano sized iron, cobalt, ruthenium and rhodium crystallites indicate that below a certain crystallite size they display a decrease in surface specific activity. This work aims to study the crystallite size effect of cobalt, supported on an industrially relevant carrier material, on activity and selectivity in the Fischer-Tropsch synthesis
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