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1
Shah, Rashed. "Zeolite-Modified Fischer-Tropsch Synthesis." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/10738.
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The improvement of the gasoline selectivity and quality with the addition of HZSM-5 to the Fe-FT process is evident from literature. The catalytic performance of the combined Fe-FT/HZSM-5 system has been observed to decline with time-on-stream, attributed to the migration of alkali from the Fe-FT catalyst tothe HZSM-5 zeolite. The catalytic performance of the combined Fe-FT/HZSM-5system has, however, been observed to considerably decline with time-on-stream, aphenomenon which has been attributed to the migration of alkali from the Fe-FT catalyst to he HZSM-5 zeolite. The objective of this study is to characterize and confirm the reported performance of the Fe-FT and combined Fe-FT/HZSM-5 catalyst systems in a stirred from top internal recycle reactor under typical high temperature FT conditions.
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Perry, Derek Michael. "FISCHER-TROPSCH SYNTHESIS IN SUPERCRITICAL PHASE CARBON DIOXIDE." OpenSIUC, 2009. https://opensiuc.lib.siu.edu/theses/155.
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The Fischer-Tropsch (FT) synthesis reaction is an increasingly valuable tool that produces very clean alternative fuels for the transportation and other industries. By utilizing a ready supply of syngas (H2 and CO mixture) from coal, natural gas, or a biomass source, the catalyzed reaction looks to be a promising alternative which could potentially end dependency on imported petroleum. The supercritical phase FT synthesis reaction has shown, in numerous other studies, to possess superior heat transfer capabilities, high desorption rates from the catalyst surface (enhancing catalyst life), and overall high mass transfer rates of hydrocarbon products, when compared with conventional gas and liquid phase results. Prior studies at SIUC have shown that the use of supercritical CO2 as a medium for the Fischer-Tropsch (FT) synthesis reaction enhances reaction rates while suppressing excess CO2 production. This phenomena was observed in gas phase batch reactions, meaning never before has a continuous flow FT synthesis with analysis of the liquid product distribution been attempted while using CO2 as the supercritical-phase medium. This project verifies the conclusions in a continuous flow mode, allowing for the collection and analysis of a liquid fraction. Additionally, this study evaluates the changes in the liquid product distribution for a variation of operating pressures including supercritical-phase reaction conditions, using pressures of 350, 800, 1000, and 1200psi and temperatures of 250, 300, and 350°C. The findings show that the influence of carbon dioxide enhance product distribution to yield a higher diesel fraction (C13 to C15), when compared to results without carbon dioxide as a medium, which favor gasoline fraction (C7 to C9). The findings also illustrate that operating in the supercritical region enhances product distribution, but depending on the solvent density, could potentially produce large amounts of oxygenates (alcohols, ketones) in the product distribution.
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Yates, Ian C. (Ian Charles). "The slurry-phase Fischer-Tropsch synthesis." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/13757.
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Lee, Hyun-Jung. "Optimization of Fischer-Tropsch plant." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/optimization-of-fischertropsch-plant(236736b1-dae6-41ea-a234-576d226beff1).html.
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Fischer-Tropsch synthesis is the technology for converting fuel feedstocks such as natural gas and coal into transportation fuels and heavy hydrocarbons. There is scope for research and development into integrated processes utilising synthesis gas for the production of a wide range of hydrocarbons. For this purpose there should be strategies for the development of Fischer-Tropsch processes, which consider both economic and technological feasibilities. The aim of this study was to optimize Fischer Tropsch Plants in order to produce gasoline and gas oil by investigating the benefits of recycling & co-feeding of unconverted gas, undesired compounds, and lighter hydrocarbons over iron-based catalysts in order to save on capital and operating costs. This involved development of FT models for both two-phase and three-phase reactors. The kinetic parameters for these models were estimated using optimization with MATLAB fitting to experimental data and these models were then applied to ASPEN HYSYS flowsheets in order to simulate nine different Fischer-Tropsch plant designs. The methodology employed involved qualitative modelling using Driving Force Analysis (DFA) which indicates the necessity of each compound for the Fischer-Tropsch reactions and mechanism. This also predicts each compounds influence on the selectivity of different products for both two-phase and three-phase reactors and for both pure feeding and co-feeding arrangements. In addition, the kinetic models for both two-phase and three-phase reactor were modified to account for parameters such as the size of catalyst particles, reactor diameter and the type of active sites used on the catalyst in order to understand and quantify their effects. The kinetic models developed can describe the hydrocarbon distributions consistently and accurately over large ranges of reaction conditions (480-710K, 0.5-2.5MPa, and H2/CO ratio: 0.5-2.5) over an iron-based catalyst for once-through processes. The effect of recycling and co-feeding on the iron-based catalyst was also investigated in the two reactor types. It was found that co-feeding unwanted compounds to synthesis gas increases the production of hydrocarbons. This recycling and co-feeding led to an increase in H2/CO feed ratio and increased selectivity towards C5+ products in addition to a slightly increased production of light hydrocarbons (C1-C4). Finally, the qualitative model is compared with the quantitative models for both two-phase and three-phase reactors and using both pure feeding and co-feeding with the same reactor conditions. According to the detailed quantitative models developed, in order to maximize hydrocarbon production pressures of 2MPa, temperatures of 450K and a H2/CO feed ratio of 2:1 are required. The ten different Fischer-Tropsch plant cases were based on Fischer-Tropsch process. FT reactor models were built in ASPEN HYSYS and validated with real FT plant data. The results of the simulation and optimization supported the proposed process plant changes suggested by qualitative analysis of the different components influence. The plants involving recycling and co-feeding were found to produce higher quantities of gasoline and gas oil. The proposed heuristic regarding the economic scale of the optimized model was also evaluated and the capital cost of the optimized FT plant reduced comparison with the real FT plant proposed by Gerard. Therefore, the recycling and co-feeding to FT reactor plant was the best efficiency to produce both gasoline and gas oil.
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Chanenchuk, Claire Ann. "Catalyst systems for the Fischer-Tropsch synthesis." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13140.
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Donnelly, Timothy Joseph. "Product distributions of the Fischer-Tropsch synthesis." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14331.
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Pokhrel, Sewa. "FISCHER- TROPSCH SYNTHESIS ON FUNCTIONALIZED CARBON NANOTUBES." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1408.
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The aim of this research was to investigate the role of chemical functionalization on carbon nanotubes surfaces and its effect on FT catalysis. Multi walled carbon nanotubes (MWNT) were first treated with acid (HCl) to remove the residual metal particles and were then functionalized using H2O2 and HNO3 to introduce oxygen-containing groups to the MWNT surface. These treatments also add defects on MWNT surface. Morphological analyses were performed on the MWNT samples with TEM and it was found that the peroxide and acid treated MWNTs showed an increase oxygen functional groups and created additional surface defects on the MWNTs. Results of FT experiments showed enhanced CO conversion, FT activity and product selectivity towards liquid hydrocarbons due to functionalization. The liquid selectivity was found to be significantly high for H2O2 treated catalyst. HNO3 treated catalyst had highest activity although selectivity to methane and CO2 was found higher than the H2O2 treated catalyst. It was observed that the chemical treatments increase the carbon chain length of the produced hydrocarbons. While comparing hydrocarbon distribution of as-produced and H2O2 treated MWNT, it was found that carbon-chain length increases for peroxide treated catalyst. Along with as-produced and functionalized nanotube, FT experiments were also conducted using B-doped sponge, un-doped sponge and N-doped CNT catalyst. B-doped sponge showed enhanced CO conversion and FT activity as compared to un-doped sponge. Conversion and product selectivity were found to be affected by temperature when test was conducted with N-CNT. Operating conditions like temperature, syngas feed flow rate and syngas ratio were also to impact the FT performance.
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Mabaso, Evans Itai. "Nanosized iron crystallites for Fischer-Tropsch synthesis." Doctoral thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/8736.
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Includes bibliographical references (p. 131-148).Fischer-Tropsch synthesis is the production of hydrocarbons from CO and H2. The catalytically active metals for industrial application are cobalt and iron. In this work iron-based catalysts were studied. To ensure maximum metal utilisation and therefore a high weight specific catalytic activity, the metal crystallites should possess large specific surface areas and that is only achievable with small metal crystallites. However, a minimum crystallite size might exist below which catalyst activity drops. Consequently, in order to investigate the role of crystallite size on the stability, the activity and selectivity of iron based catalysts, supported catalysts with a known narrow metal crystallite size distribution were prepared via precipitation in water-in-oil microemulsions in which water-to-surfactant ratio was the main design parameter. The study was subdivided into firstly characterisation of a suitable water-in-oil microemulsion system. Secondly preparation of nanosized oxidic iron crystallites with controlled crystallite size via precipitation in water-in-oil microemulsion. Thirdly preparation of the supported catalyst using the same but selected microemulsion systems. Finally catalyst testing under Fischer-Tropsch reaction conditions in a fixed bed reactor. A strictly linear relationship between water-to-surfactant ratio and crystallite size was observed. The catalyst preparation technique for unsupported iron oxides resulted in uniform nanocrystallites tailored to a size range of 2-16 nm. The morphology of the crystallites on supports remained largely unchanged upon reductive pretreatment. This made catalysts prepared in microemulsions ideally suitable for investigating the effect of crystallite size during Fischer-Tropsch synthesis.
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Pardo-Tarifa, Fatima. "Cobalt catalyst supports for Fischer-Tropsch synthesis." Doctoral thesis, KTH, Skolan för kemivetenskap (CHE), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-215121.
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In the Fischer-Tropsch (FT) synthesis, CO and H2 (synthesis gas) are converted into hydrocarbons that can be further upgraded to high-quality fuels and chemicals. Different carbon sources such as natural gas, coal and biomass can be used as feed-stocks for the synthesis gas. In commercial applications, supported cobalt catalysts are commonly used in the FT synthesis, especially when the synthesis gas emanates from natural gas and when the desired final product is diesel. The activity and selectivity of a cobalt catalyst is dependent on several parameters, one of them being the support. The present thesis is focused on the design, synthesis and characterization of alumina and silica materials (with and without Ce and Zr promoters) with non-conventional morphology, and evaluation of their feasibility as cobalt supports in the FT synthesis. Ce- and Zr-alumina nanoparticles were synthesized by co-precipitation in water-in-oil microemulsion. The obtained product is amorphous alumina with highly dispersed promoters, resulting in strong cobalt-support interactions and low cobalt reducibility. By increasing the calcination temperature of the Ce-promoted support, crystalline CeO2 is obtained which apparently increases the cobalt reducibility and thereby the catalytic activity (per gram catalyst). The small pore size of the materials may induce diffusion limitations on the reactants arrival and/or result in very small cobalt particles, which favour methane over long-chain hydrocarbons. Successful preparations of pore expanded mesoporous silicas with 1D, 2D and 3D pore structures via the atrane route, combined with the addition of swelling agents, have been demonstrated. The advantage of this method is that pore expansion can be achieved at mild conditions and there is no need for a post-synthesis process using an autoclave system. In larger silica support pores, larger cobalt particles will be formed and the weaker the cobalt-support interactions will be. This generally results in a higher cobalt reducibility for larger-pore supports and thereby a higher catalytic activity.QC 20171004
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Doss, Tamer. "Low severity Fischer-Tropsch synthesis for the production of synthetic hydrocarbon fuels." Thesis, Aston University, 2012. http://publications.aston.ac.uk/19135/.
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Currently, the main source for the production of liquid transportation fuels is petroleum, the continued use of which faces many challenges including depleting oil reserves, significant oil price rises, and environmental concerns over global warming which is widely believed to be due to fossil fuel derived CO2 emissions and other greenhouse gases. In this respect, lignocellulosic or plant biomass is a particularly interesting resource as it is the only renewable source of organic carbon that can be converted into liquid transportation fuels. The gasification of biomass produces syngas which can then be converted into synthetic liquid hydrocarbon fuels by means of the Fischer-Tropsch (FT) synthesis. This process has been widely considered as an attractive option for producing clean liquid hydrocarbon fuels from biomass that have been identified as promising alternatives to conventional fossil fuels like diesel and kerosene. The resulting product composition in FT synthesis is influenced by the type of catalyst and the reaction conditions that are used in the process. One of the issues facing this conversion process is the development of a technology that can be scaled down to match the scattered nature of biomass resources, including lower operating pressures, without compromising liquid composition. The primary aims of this work were to experimentally explore FT synthesis at low pressures for the purpose of process down-scaling and cost reduction, and to investigate the potential for obtaining an intermediate FT synthetic crude liquid product that can be integrated into existing refineries under the range of process conditions employed. Two different fixed-bed micro-reactors were used for FT synthesis; a 2cm3 reactor at the University of Rio de Janeiro (UFRJ) and a 20cm3 reactor at Aston University. The experimental work firstly involved the selection of a suitable catalyst from three that were available. Secondly, a parameter study was carried out on the 20cm3 reactor using the selected catalyst to investigate the influence of reactor temperature, reactor pressure, space velocity, the H2/CO molar ratio in the feed syngas and catalyst loading on the reaction performance measured as CO conversion, catalyst stability, product distribution, product yields and liquid hydrocarbon product composition. From this parameter study a set of preferred operating conditions was identified for low pressure FT synthesis. The three catalysts were characterized using BET, XRD, TPR and SEM. The catalyst selected was an unpromoted Co/Al2O3 catalyst. FT synthesis runs on the 20cm3 reactor at Aston were conducted for 48 hours. Permanent gases and light hydrocarbons (C1-C5) were analysed in an online GC-TCD/FID at hourly intervals. The liquid hydrocarbons collected were analyzed offline using GC-MS for determination of fuel composition. The parameter study showed that CO conversion and liquid hydrocarbon yields increase with increasing reactor pressure up to around 8 bar, above which the effect of pressure is small. The parameters that had the most significant influence on CO conversion, product selectivity and liquid hydrocarbon yields were reactor temperature and catalyst loading. The preferred reaction conditions identified for this research were: T = 230ºC, P = 10 bar, H2/CO = 2.0, WHSV = 2.2 h-1, and catalyst loading = 2.0g. Operation in the low range of pressures studied resulted in low CO conversions and liquid hydrocarbon yields, indicating that low pressure BTL-FT operation may not be industrially viable as the trade off in lower CO conversions and once-through liquid hydrocarbon product yields has to be carefully weighed against the potential cost savings resulting from process operation at lower pressures.
11
Campen, Adam. "Fly Ash Zeolite Catalyst Support for Fischer-Tropsch Synthesis." OpenSIUC, 2012. https://opensiuc.lib.siu.edu/dissertations/610.
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This dissertation research aimed at evaluating a fly ash zeolite (FAZ) catalyst support for use in heterogeneous catalytic processes. Gas phase Fischer-Tropsch Synthesis (FTS) over a fixed-bed of the prepared catalyst/FAZ support was identified as an appropriate process for evaluation, by comparison with commercial catalyst supports (silica, alumina, and 13X). Fly ash, obtained from the Wabash River Generating Station, was first characterized using XRD, SEM/EDS, particle size, and nitrogen sorption techniques. Then, a parametric study of a two-step alkali fusion/hydrothermal treatment process for converting fly ash to zeolite frameworks was performed by varying the alkali fusion agent, agent:flyash ratio, fusion temperature, fused ash/water solution, aging time, and crystallization time. The optimal conditions for each were determined to be NaOH, 1.4 g NaOH: 1 g fly ash, 550 °C, 200 g/L, 12 hours, and 48 hours. This robust process was applied to the fly ash to obtain a faujasitic zeolite structure with increased crystallinity (40 %) and surface area (434 m2/g). Following the modification of fly ash to FAZ, ion exchange of H+ for Na+ and cobalt incipient wetness impregnation were used to prepare a FTS catalyst. FTS was performed on the catalysts at 250 - 300 °C, 300 psi, and with a syngas ratio H2:CO = 2. The HFAZ catalyst support loaded with 11 wt% cobalt resulted in a 75 % carbon selectivity for C5 - C18 hydrocarbons, while methane and carbon dioxide were limited to 13 and 1 %, respectively. Catalyst characterization was performed by XRD, N2 sorption, TPR, and oxygen pulse titration to provide insight to the behavior of each catalyst. Overall, the HFAZ compared well with silica and 13X supports, and far exceeded the performance of the alumina support under the tested conditions. The successful completion of this research could add value to an underutilized waste product of coal combustion, in the form of catalyst supports in heterogeneous catalytic processes.
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Tymowski, Benoît de. "Fischer Tropsch synthesis on conductive silicon carbide based support." Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAF019/document.
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La synthèse de Fischer-Tropsch (SFT) permet la transformation d'un mélange de gaz de synthèse, i.e. H2 et CO, issu des différentes matières premières (charbon, gaz naturel ou biomasse) en hydrocarbures synthétiques. Les catalyseurs généralement utilisés en SFT sont à base de fer ou de cobalt supporté sur alumine ou silice. Dans ce travail, le carbure de silicium (SiC) a été proposé comme nouveau support de remplacement pour la SFT. Les résultats obtenus ont montré que les catalyseurs à base de cobalt supporté sur du SiC, contenant essentiellement des mésopores, sont actifs et sélectifs pour la réaction de SFT par rapport aux catalyseurs traditionnels supportés sur alumine ou silice. L'activité en SFT peut être améliorée en utilisant de l'éthanol comme solvant d'imprégnation ou en ajoutant un promoteur tel que le ruthénium. Le dopage du support de départ par du Ti02 contribue également à une forte augmentation de l'activité en SFT grâce à la formation de petites particules de cobalt présentant une activité en SFT plus élevée. La forte interaction entre le Ti02 et le cobalt permet également d'améliorer d'une manière considérable la stabilité du catalyseurThe Fischer-Tropsch synthesis (FTS) allows the transformation of a mixture of synthesis gas, i.e. H2 and CO, into valuable liquid hydrocarbons. The catalysts generally used in FTS are based on iron or cobalt supported on alumina or silica. ln the present work, silicon carbide (SiC) has been proposed as a replacement media to traditional supports. The results obtained indicate that the mesoporous SiC containing cobalt catalyst exhibits a good FTS activity and an extremely high selectivity towards liquid hydrocarbons compared to other FTS catalysts supported on alumina or silica. The FTS activity on the Co/SiC catalyst can be improved by changing the impregnation solvent or by promoting the cobalt phase with trace amount of noble metal. The doping of the SiC support with Ti02 phase also significantly improves the FTS activity keeping a similar high selectivity thanks to the formation of small cobalt particles in contact with the Ti02 phase
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Perry, Derek. "Fischer-Tropsch synthesis in supercritical phase carbon dioxide /." Available to subscribers only, 2009. http://proquest.umi.com/pqdweb?did=1966544141&sid=1&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Dasgupta, Debalina. "ENHANCING GAS PHASE FISCHER-TROPSCH SYNTHESIS CATALYST DESIGN." Available to subscribers only, 2008. http://proquest.umi.com/pqdweb?did=1674093841&sid=6&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Thesis (Ph. D.)--Southern Illinois University Carbondale, 2008."College of Engineering." Keywords: Bimetallic, Catalysts, Iron-cobalt, Fischer-Tropsch synthesis, Ruthenium Includes bibliographical references (p. 123-134). Also available online.
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Alagiri, Praveenkumar. "FISCHER-TROPCH SYNTHESIS ON COMMERCIALLY AVAILABLE CARBON NANOTUBES." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/2052.
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The aim of this research is to investigate the role of chemical functionalization on carbon nanotubes and its effect on the FT synthesis. Multi walled carbon nanotubes (MWNT) bought from the market were functionalized using HNO3 to introduce oxygen-containing groups to the MWNT surface. This treatment also adds defects on MWNT surface. Carboxyl functionalized multiwall carbon nanotubes (-COOH) and hydroxyl functionalized multiwall carbon nanotubes (-OH) were also bought from the market and used in the experiments, Results of FT experiments showed very high CO conversion. Fischer Tropsch activity and product selectivity were towards liquid hydrocarbons due to functionalization. Highly desired product distribution were obtained due to chemical functionalization of CNTs. The performance of all the functionalized Multi wall nanotubes was better than the pure Multi wall nanotubes. Operating conditions like temperature, syngas feed flow rate and syngas ratio were also to impact the FT performance.
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Rafiq, Muhammad Hamid. "Experimental Studies and Modeling of Synthesis Gas Production and Fischer-Tropsch Synthesis." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16572.
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Indirect route can be used to convert abundant natural resources such as natural gas (NG), coal and biomass to synthetic fuels (referred to as gas-to-liquid (GTL), coalto- liquid (CTL) and biomass-to-liquid (BTL)). It is currently one of the most effective solutions to the problem of finding suitable substitutes for liquid clean fuels. In this work, an investigation on the production of synthetic fuel from gaseous hydrocarbons (HCs)/bio-HCs and liquid bio-HCs on a small-scale unit has been carried out. The research project consists of two major parts, a modified version of a plasma-assisted catalytic partial oxidation (CPO) gliding arc (GlidArc) reactor and a thermally stable single-tube fixed-bed Fischer−Tropsch (FT) reactor. The potential for the CPO of methane to produce synthesis gas (syngas) was studied both experimentally and thermodynamically at a fixed pressure (1 bar) and electric power (0.3 kW). The investigations were performed in a partially adiabatic plasma-assisted (nonthermal) GlidArc reactor, using a Ni-based catalyst. Two cases were studied: in the first, normal air (molar ratio of O2/N2=21/79) was used, whereas enriched air (O2/N2=40/60) was utilized in the second. The individual effect of the O2/CH4 molar ratio, gas hour space velocity (GHSV) and bed exiting temperature (Texit) was studied for both cases. The main trends of the CH4 conversion, the syngas (H2 and CO) yield and the thermal efficiency of the reactor based on the lower heating value (LHV) were analyzed and compared. A numerical investigation of the CPO of methane to syngas using a GlidArc reactor was also studied. A 2D heterogeneous plug-flow model with radial dispersion and no gradients inside the catalyst pellet are used, including the transport equations for the gas and solid phase and reaction rate equations. The governing equations of this model formed a set of stationary differential algebraic equations coupled with the non-linear algebraic equations, and were solved numerically using in-house MATLAB code. Model results of CPO of methane were compared to previous experimental data with the GlidArc reactor found in the literature. A close match between the calculated and experimental results for temperature, reactant (CH4 and O2) conversion, H2 and CO yields and species molefraction were obtained. The developed model was extended to predict and quantify the influence of the GHSV as well as determine the influence of the reactor energy density (RED), the O2/CH4 molar ratio and the O2/N2 molar ratio. The predicted behaviors for the species mole-fraction, reactants conversion, H2 and CO yields and temperature along the length of the reactor have been analyzed. Furthermore, FT synthesis of a model biosyngas (33% H2, 17% CO and 50% N2) in a single tube fixed-bed FT reactor was investigated. The FT reactor consisted of a shell and tube with high-pressure boiling water circulating throughout the shell. A spherical unpromoted cobalt catalyst was used with the following reaction conditions: a wall temperature of 473 K, a pressure of 20 bars and a GHSV of 37 to 180 NmL/(gcat.h). The performance of the FT reactor was also validated by developing a 2D pseudo-homogeneous model that includes transport equations and reaction rate equations. Good agreement between the model predictions and experimental results were obtained. This developed model was extended to predict and quantify the influence of the FT kinetics as well as determine the influence of the tube diameter and the wall temperature. The predicted behaviors for CO and H2 conversion, productivity of HCs (mainly CH4 and C5 +) and fluid temperature along the axis of the reactor have been analyzed. In addition, the initial tests results are presented for the conversion of waste cookingoil (WCO) to biosyngas by CPO over a granular Ni-based catalyst. Additionally, autothermalreforming (ATR) of propane with water and normal air was also carried out.The investigations were performed in a partially adiabatic plasma-assisted (non-thermal)GlidArc reactor at fixed pressure (1 bar) and electric power (0.3 kW). Detailed axial temperaturedistributions, product concentrations, reactant conversions, H2 and CO yield,H2/CO ratio and thermal efficiency, as a function of the cold and hot WCO flow rate, thewater flow rate and the time on stream were studied. Propane and normal air were usedas oxidizing components to maintain autothermal operation. Finally, an investigation of the influence of process conditions on the production ofsyngas from model biogas (molar ratio of CH4/CO2=60/40) through partial oxidationover a granular Ni-based catalyst was explored. The investigations were performed in apartially adiabatic plasma-assisted (non-thermal) GlidArc reactor in a transitional flowregime at a fixed pressure (1 bar) and electric power (0.3 kW). The emphasis of this investigationwas on an experimental study and a comparative thermodynamic analysis. Theequilibrium compositions were calculated using a Lagrange multiplier and resulted in thedevelopment of systems of non-linear algebraic equations, which were solved numericallyusing the MATLAB function “fmincon”. Two cases were studied: normal air (molar ratioof O2/N2=21/79) and enriched air (O2/N2=40/60). The individual effects of the O2/CH4molar ratio and the Texit were studied in both cases. The main trends of the CH4 conversion,the syngas yield, the H2/CO ratio and the thermal efficiency of the reactor wereanalyzed.
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Romar, H. (Henrik). "Biomass gasification and catalytic conversion of synthesis gas:characterisation of cobalt catalysts for Fischer-Tropsch synthesis." Doctoral thesis, Oulun yliopisto, 2015. http://urn.fi/urn:isbn:9789526208015.
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Abstract Biomass gasification as a thermochemical treatment method is typically used for heat and power production. Instead of burning the producer gas, it can be converted to added-value products, i.e to fuels and chemicals. One such conversion is the catalytic Fischer-Tropsch synthesis (FTS) which converts synthesis gas to a chain of aliphatic hydrocarbons (FT diesel) as studied in this thesis. This requires, however, proper cleaning steps of producer gas, such as the removal of tar compounds and other impurities. These cleaning steps are not considered in this thesis. The first goal of the thesis was to determine the tar content in the producer gas from a small scale biomass gasifier. This subject is discussed in Paper I. The second and main goal of the thesis was the preparation and characterization of cobalt (or iron) catalysts for catalytic conversion of a gas mixture close to the synthesis as discussed in Papers II-V. The overall aim of the second part was to study the effects of promoters on the reducibility of cobalt and the effects of different calcination conditions on the degree of reduction and size of the metallic cobalt particles. In this later part different catalytic supports were used. According to the results of the thesis, naphthalene and toluene were the main tar compounds in the producer gas representing almost 80 % of the GC detected tar compounds. Only traces of polycyclic aromatic compounds were detected and no phenolic compounds were found in the gas. Further, a number of supported heterogeneous catalysts for FTS using cobalt (Co) or in some cases iron (Fe) as the active metal were prepared and characterized. These catalysts were supported on alumina (Al2O3), titanium dioxide (TiO2) or silicon carbide (SiC). Catalysts were promoted with Ru, Re or Rh in the concentrations of 0, 0.2, 0.5, and 1.0 mass-%. Several characterization methods (such as H2-TPR, catalytic activity measurements, N2 physisorption, CO chemisorption, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD)) were used to find answers to the behaviour of these catalysts under selected conditions and in the model reaction of FTS. Based on the results, there are significant differences in the characteristics of the catalysts, the differences are dependent of the supports used, promoters added and calcination conditions used. The properties of the support, especially the pore size distribution will effect the distribution of products formed in the Fischer-Tropsch synthesis. Addition of promoters and variatons in calcination conditions will effect the dispersion and the particle size of the active metalTiivistelmä Biomassan kaasutus on termokemiallinen prosessi, jota käytetään pääosin sähkön- ja lämmöntuotannossa. Polton sijaan kaasutuksessa muodostuva synteesikaasu voidaan puhdistaa ja hyödyntää edelleen katalyyttisesti polttoaineiden ja kemikaalien valmistuksessa. Eräs mahdollisuus synteesikaasun hyödyntämiseen on Fischer-Tropsch synteesi (FTS), jossa koboltti- tai rautakatayyteillä voidaan tuottaa alifaattisia hiilivetyketjuja (FT-dieseliä), mitä on tutkittu tässä työssä. FT-synteesi vaatii kuitenkin puhtaan tuotekaasun ja sen vuoksi tervayhdisteet ja muut epäpuhtaudet on poistettava kaasusta. Kaasun puhdistusta ei ole kuitenkaan tutkittu tässä työssä. Työn ensimmäisenä tavoitteena oli määrittää biomassan kaasutuksessa käytettävän pienikokoisen myötävirtakaasuttimen kaasun koostumus ja tervayhdisteet ja niiden pitoisuudet (julkaisu I). Toisena, ja tämän työn päätavoitteena oli Fischer-Tropsch -synteesissä käytettävien koboltti- ja rautakatalyyttien valmistus ja karakterisointi sekä käyttö synteesikaasun katalyyttisessä konvertoinnissa (julkaisut II-V). Erityisesti tutkittiin promoottorimetallien ja kalsinointiolosuhteiden vaikutusta koboltin pelkistymiseen ja kobolttimetallipartikkelien kokoon. Lisäksi tutkittiin ja vertailtiin erilaisia tukiaineita. Työn tulosten perusteella naftaleiini ja tolueeni olivat pääasialliset tervayhdisteet myötävirtakaasuttimen tuotekaasussa ja niiden osuus oli yli 80 % kaasukromatografisesti havaittavista tervayhdisteistä. Lisäksi havaittiin pieniä määriä polysyklisiä aromaattisia yhdisteitä, kun taas fenolisia yhdisteitä ei havaittu tuotekaasussa. Työssä valmistettiin ja karakterisoitiin lukuisa määrä erilaisia FT-katalyyttejä, joissa aktiivisena metallina oli koboltti tai rauta. Katalyyteissä tukiaineena oli alumiinioksidi (Al2O3), titaanidioksidi (TiO2) tai piikarbidi (SiC) ja promoottorimetallina joko Ru, Re tai Rh (pitoisuudet 0, 0.2 tai 1.0 massa-%). Katalyyttien karakterisointiin käytettiin useita menetelmiä, kuten H2-TPR, N2-adsorptio, CO-kemisorptio, XPS, XRD ja lisäksi määritettiin katalyyttien aktiivisuus ja selektiivisyys valituissa olosuhteissa FT-synteesin mallireaktioissa. Tulosten perusteella katalyyttien välillä havaittiin selkeitä eroja riippuen käytetystä tukiaineesta, promoottorista ja kalsinointiolosuhteista. Tukiaineen ominaisuudet, erityisesti huokoskokojakauma vaikuttavat FT-synteesin tuotejakaumaan. Promoottorien lisäys katalyyttiin sekä kalsinointiolosuhteet vaikuttavat lisäksi dispersioon ja aktiivisen metallien partikkelikokoon
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Carron, David. "FISCHER-TROPSCH SYNTHESIS IN SUPERCRITICAL PHASE CARBON DIOXIDE: DEACTIVATION STUDIES." OpenSIUC, 2011. https://opensiuc.lib.siu.edu/theses/643.
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ABSTRACT This thesis presents the results of investigations regarding the effect of supercritical CO2 on the long term activity, life and deactivation rates of an Fe-Zn-K catalyst during Fischer Tropsch Synthesis from syngas (H2:CO =1:1) typically produced from coal gasification. Previous studies at SIUC on FTS in Supercritical CO2 (SC-CO2) have shown that CH4 selectivity was inhibited and with the presence of excess CO2, the WGS reaction was reversed. This increased the carbon economy as result of the reduction in parasitic loss of CO to CO2. In addition, it was observed that the conversion of CO, under these pressures and CO2 dilution, was significantly enhanced. Studies in a continuous flow system showed the use of SC-CO2 affected the distribution of hydrocarbons, mainly producing heavier hydrocarbons (diesel fuel). In this thesis, results from four long term experiments (21-28 day) varying the CO2:syngas ratio are reported. The experiments were conducted at 350 oC, 1200 psi with a feed rate of 200sccm in a fixed bed supercritical reactor with a volume of 150 cc. The results show that the conversion of syngas increased from 47% to 95% at the optimum ratio 5:1 (CO2:Syngas). The steady state reaction rate constant also increased 4.756 times the baseline run from 0.021215 min-1 to 0.100907 min-1, for pure syngas and a CO2:syngas ratio of 5:1 respectively. The deactivation rate did not improve with the use of supercritical CO2; however, the life span of the catalyst more than doubled that of the base line run with an increase in SC- CO2. Product tailoring can also be performed by simply changing the SC-CO2:Syngas ratio. Ratios less than 5:1 will yield a product distribution of predominately alcohols, ratios greater than 5:1 produce heavier hydrocarbons. Both of these product distributions can be beneficial, but for this research a ratio of 5:1 yielded the desired product distribution of light to heavy hydrocarbons generically known as gasoline and diesel fuel. Liquid selectivity was observed to increase with CO2 content in the feed upto a CO2:syngas ratio of 5:1, thereafter it declined slightly. CO2 is produced in the experiment of pure syngas with no Sc-CO2, however the introduction of Sc-CO2 resulted in the consumption of CO2 for the production of hydrocarbons. The methane selectivity was found to monotonically decrease with the increase in CO2 content in the feed. With oil prices increasing, the use of SC- CO2 as a reaction media for FTS is showing more promise in providing liquid fuels more effectively. The evidence of consumption of CO2 means that CO2 does not need to be removed from the syngas feed stream after the gasification and water gas shift unit processes. The increase in the observed life of the catalyst under supercritical conditions will ultimately reduce the operating cost as less material will be needed to produce the same amount of product allowing for FTS to become economically competitive.
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Huh, Billy K. "Structural effects in Fischer-Tropsch synthesis over bimetallic supported catalysts." Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/11832.
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Teoh, Wey Yang Chemical Sciences & Engineering Faculty of Engineering UNSW. "Flame spray synthesis of catalyst nanoparticles for photocatalytic mineralisation of organics and Fischer-Tropsch synthesis." Awarded by:University of New South Wales. School of Chemical Sciences and Engineering, 2007. http://handle.unsw.edu.au/1959.4/28259.
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In this thesis, a range of TiO2-based photocatalysts and cobalt-based Fischer-Tropsch (FT) catalysts were developed and synthesised via the one-step Flame Spray Pyrolysis(FSP). The work starts with the demonstration of bare TiO2 nanoparticles synthesis with controlled characteristics such as specific surface areas, crystallite sizes and anatase content. A comparative study was carried out by benchmarking with commercial Degussa P25 TiO2. The FSP TiO2 was shown to be more efficient in mineralising pollutants requiring direct charge transfer such as the saccharides, while P25 was better for mineralising alcoholic and aromatic compounds. Both catalysts were equally as active in mineralising carboxylic acids. Upon identifying the optimal synthesis of bare TiO2, an in situ co-precipitation of highly dispersed Pt on TiO2 was carried out in the flame. Deposition of Pt resulted in enhanced photocatalytic performance as a result of efficient charge trappings. It is highlighted here the inter-relationship between Pt oxidation states and the TiO2photocatalysis of carboxylic acid, alcohol and aromatic compounds. Depending on the mineralisation path adopted by the model organic compounds, they were shown to have direct influence on the Pt oxidation states. These oxidation states in turn affect the mineralisation rates of the organic compounds. Substitutional-doping of TiO2 with Fe(III) with tunable bandgap was also possible by FSP synthesis. The high temperature synthesis coupled with rapid quenching resulted in 5 times higher solubility limit (Fe/Ti = 0.05) than that previously reported in the literature. Under visible light irradiation, FSP-made Fe-TiO2 improved the photocatalytic mineralisation of oxalic acid by more than 6 times, with respect to P25 and FSP TiO2. Furthermore, the photocatalyst was reusable over a number of repetitions with minimal leaching or loss in activity. The last part of the work concerns the development of bare and Ru-doped Co-ZrO2 catalysts, where cobalt was finely dispersed within the zirconia matrix. Doping of Ru enhanced significantly the reducibility of cobalt, reducing even the embedded cobalt beneath the zirconia surface. It also increased the extent of CO-chemisorption and as such, enhanced the FT activity. This is the first time, catalysts of such type is synthesised and tested for FT reaction.
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Lualdi, Matteo. "Fischer-Tropsch Synthesis over Cobalt-based Catalysts for BTL applications." Doctoral thesis, KTH, Kemisk teknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102304.
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Fischer-Tropsch synthesis is a commercial technology that allows converting synthesis gas, a mixture of CO and H2, into fuels and chemicals. This process could be one of the actors in the reduction of oil dependency of the transportation sector. In fact, it has great potential for producing synthetic fuels also from renewable sources, such as biomass, after its thermochemical conversion (gasification) into synthesis gas. Concerning the quality of a diesel fuel produced with this technology, it has a lower local environmental impact than conventional diesel, since it is practically free of sulphur and nitrogen compounds and yields lower exhaust emissions of hydrocarbons, CO and particulates. The present study focuses on the use of cobalt-based catalysts for the production of diesel. In particular, it looks upon correlation between product selectivities when varying the catalyst properties and the effect of process parameters, such as a low H2/CO ratio, typical of a biomass-derived synthesis gas, and the water partial pressure. Different cobalt-based catalysts, with different properties, such as conventional 3-dimensional porous network supports (γ-Al2O3, α-Al2O3, TiO2, SiO2), Co-loading, preparation technique, etc., were investigated in the Fischer–Tropsch reaction at industrially relevant process conditions. For a set of process conditions, a linear relationship seems to exist between the selectivity to methane (and other light products) and higher hydrocarbons (identified by the industrially relevant parameter SC5+, selectivity to hydrocarbons with more than 4 carbon atoms) indicating a common precursor. Ordered mesoporous materials (SBA-15), characterized by a 1-dimensional mesoporous network, were tested as model supports and showed the possibility of occurrence of CO-diffusion limitations at diffusion distances much shorter than those required for conventional 3-dimensional porous network supports. The linear relationship mentioned above, derived for conventional supports, was shown to be an efficient tool for indicating whether measured selectivities are affected by CO-diffusion limitations. Some of the catalysts were exposed to H2-poor syngas and to external water addition and the effects on the selectivity relationships were investigated. Furthermore, the possibility of internal water-gas shift of a H2-poor syngas with mixtures of Co/γ-Al2O3 and a Cu/ZnO/Al2O3 catalyst was investigated both as a technical solution for direct use of a model bio-syngas in the Fischer-Tropsch synthesis, and as a means to study the effect of indigenous water removal on the reaction rate to hydrocarbons. It was found that removal of indigenously produced water slows down the reaction rate significantly. Lastly, the effect of water partial pressure on the Fischer–Tropsch rate of the Co catalyst supported on narrow-pore γ-Al2O3, on its own, was studied. Inlet water partial pressure was varied by external water vapor addition at different H2/CO molar ratios ranging from 1 to 3. The effect of water showed to be positive on the rate for all the H2/CO ratios, but more significantly at H2-poor conditions. The nature of this positive effect on the rate seems to be unrelated to changes in amounts of amorphous polymeric carbon detectable by temperature-programmed hydrogenation of the spent catalyst.QC 20120914
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Mcausland, Donald Euan Reynolds. "Arynes in synthesis : new reaction and precursor development." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/arynes-in-synthesisnew-reaction-and-precursor-development(1f59c4ec-dc6d-487b-9bc4-c5a99d5bc030).html.
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The arylation of readily accessible N-tosyl hydrazones has been achieved using arynes generated in situ under mild conditions. The resulting N-tosyl-N-aryl hydrazones undergo a one-pot Fischer indole reaction on the addition of acid, giving a synthesis of protected indoles that avoids handling unstable intermediates and arylhydrazines. A new route to functionalised 2-(trimethylsilyl)phenyl triflate aryne precursors via Suzuki cross-coupling has been developed. The method allows the incorporation of a wide range of aryl and heteroaryl groups and reactions of arynes generated from these novel precursors have been demonstrated, including a cyclotrimerisation and a fluorenone synthesis. Work was also undertaken on aryne σ-insertion reactions. The addition of benzyne to ynamides was found to result in its net insertion between the nitrogen and acetylene species. The reaction proceeds from attack at the terminal carbon in an analogous manner to C(sp)–O insertions.
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Borg, Øyvind. "Role of Alumina Support in Cobalt Fischer-Tropsch Synthesis." Doctoral thesis, Norwegian University of Science and Technology, Department of Chemical Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1602.
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Pienaar, Andrew. "Metal carboxylate complexes relevant to the Fischer-Tropsch synthesis." Thesis, Link to the online version, 2005. http://hdl.handle.net/10019/1158.
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Paul, Uchenna Prince. "Microkinetic Model of Fischer-Tropsch Synthesis on Iron Catalysts." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2535.pdf.
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Petersen, Anna Paula. "Alumina-modified cobalt catalysts for the Fischer-Tropsch synthesis." Doctoral thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29395.
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In the Fischer-Tropsch process, valuable hydrocarbons are produced using the basic starting materials hydrogen and carbon monoxide, which can be derived from alternative carbon sources such as coal, gas or biomass [1]. Although this process has been studied for almost a century, the effects of the support material on activity, selectivity and stability of the catalyst remain obscure. This study aims to gain fundamental insights into the effect of metal-support interactions in cobalt alumina based Fischer-Tropsch catalysts. To accomplish this, the effects of metal-support interactions have to be isolated from possible convoluting effects of the metal crystallite size and support porosity. This is achieved by preparing inverse-model catalysts, in which the support is deposited onto the metal, in contrast to conventional supported catalysts, in which the metal phase is deposited onto a porous support [2]. Cobalt alumina inverse-model catalysts were prepared by incipient wetness impregnation of cobalt oxide with aluminium sec-butoxide. The alumina loading was varied systematically between 0 and 2.5 wt% Al. The catalysts were characterised by X-ray diffraction (XRD), Transmission electron microscopy (TEM), H2 -chemisorption, and X-ray absorption near edge spectroscopy (XANES). The catalyst reducibility was studied by temperature programmed reduction (TPR), in situ (XRD) and in situ (XANES) experiments. The catalytic performance for the Fischer-Tropsch synthesis was studied in a slurry reactor under industrially relevant conditions. The alumina modification was found to prevent sintering and decrease the reducibility of the catalysts. With increasing alumina loading, and increasing calcination temperature, reduction peaks shifted to higher temperatures and peaks with maxima above 400 ˝C appeared in the TPR. The kinetic evaluation showed that the decreased reducibility was due to a decrease in the pre-exponential factor, which suggests that the alumina modification hindered hydrogen activation and/or nucleation of reduced cobalt phases. The activity of the catalysts for the FT reaction was found to increase with increasing alumina loading. This was likely an effect of the increase in metal dispersion upon alumina modification. Furthermore, alumina-modified catalysts had a higher C5+ and olefin selectivity, and lower methane selectivity. Pyridine-TPD experiments showed that the alumina modification introduced Lewis acid sites to the cobalt catalysts. Lewis acid sites may interact with adsorbed CO thereby weakening the C-O bond and facilitating CO dissociation. This was supported by CO-TPR experiments, which revealed that alumina-modified catalysts had an increased activity for the surface catalysed Boudouard reaction. It is concluded that the alumina modification increased the rate of CO dissociation on metallic cobalt. An increased rate of CO dissociation may lead to coverage of the metal surface with carbon thereby decreasing hydrogenation and shifting the product selectivity towards high molecular weight products. Hence, alumina may promote the selectivity of cobalt catalysts via a synergistic effect.
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Soti, Madhav. "Fischer - Tropsch Synthesis in Supercritical phase Carbon Dioxide: Recycle Rates." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1410.
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With increasing oil prices and attention towards the reduction of anthropogenic CO2, the use of supercritical carbon dioxide for Fischer Tropsch Synthesis (FTS) is showing promise in fulfilling the demand of clean liquid fuels. The evidence of consumption of carbon dioxide means that it need not to be removed from the syngas feed to the Fischer Tropsch reactor after the gasification process. Over the last five years, research at SIUC have shown that FTS in supercritical CO2 reduces the selectivities for methane, enhances conversion, reduces the net CO2 produces in the coal to liquid fuels process and increase the life of the catalyst. The research has already evaluated the impact of various operating and feed conditions on the FTS for the once through process. We believe that the integration of unreacted feed recycle would enhance conversion, increase the yield and throughput of liquid fuels for the same reactor size. The proposed research aims at evaluating the impact of recycle of the unreacted feed gas along with associated product gases on the performance of supercritical CO2 FTS. The previously identified conditions will be utilized and various recycle ratios will be evaluated in this research once the recycle pump and associated fittings have been integrated to the supercritical CO2 FTS. In this research two different catalysts (Fe-Zn-K, Fe-Co-Zn-K) were analyzed under SC-FTS in different recycle rate at 350oC and 1200 psi. The use of recycle was found to improve conversion from 80% to close to 100% with both catalysts. The experiment recycle rate at 4.32 and 4.91 was clearly surpassing theoretical recycle curve. The steady state reaction rate constant was increased to 0.65 and 0.8 min-1 for recycle rate of 4.32 and 4.91 respectively. Carbon dioxide selectivity was decreased for both catalyst as it was converting to carbon monoxide. Carbon dioxide consumption was increased from 0.014 to 0.034 mole fraction. This concluded that CO2 is being used in the system and converting which created the concentration of the feed gas higher inside the reactor. The research has provided the best conditions for the enhanced conversion while minimizing CO2 formation. Though this research was not able to provide the optimal recycle rate it have created the path for the future research to proceed in the right direction. This reduction and utilization of CO2 will help to reduce the cost of carbon dioxide removal and saves the environment from carbon dioxide emission.
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Halfacre, Kyle Alan. "Synthesis of Liquid Fuels Over Carbon Nanotube Catalysts." OpenSIUC, 2012. https://opensiuc.lib.siu.edu/theses/907.
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The focus of this research was to investigate the role of carbon nanotubes as active catalysts in the Fischer-Tropsch reaction to derive liquid fuels from synthesis gas. Carbon nanotubes (CNTs) have unique structural and mechanical properties that make them ideal catalyst supports, but they also exhibit catalytic potential as well. This study implored the use of multi-walled CNTs on different substrates and single-walled CNTs grown from various precursors to analyze the effectiveness of the CNTs in FT synthesis. Multi-walled nanotubes (MWNTs) were tested on two different substrates: alumina pellets and inconel. The MWNTs on the alumina substrate yielded nearly all alkane and alkene products, with very little aromatic products. The amount of converted syngas reached 97% but had a high liquid product selectivity to methane, at roughly 57%. The MWNTs on inconel substrate produced nearly 80% aromatic products in one stage of the experiment, while the other three stages produces almost all alkane products with little oxygenates. Much of the liquid product yield (upwards of 73%) was between C10 and C21, which is ideal for diesel fuel. Single-walled nanotubes (SWNTs) were also tested in the FTS. All of the SWNTs were tested under a series of 6 temperatures, 300psig, and a syngas ratio of 1:1. Iron, nickel, and cobalt, which have all been proven as effective FT catalysts, were tested in trace amounts with CNTs. Fe-SWNTs (ferrocene assisted SWNTs) yielded a product of 100% C7 and C8 carbon species at two of the temperatures while 3 of the temperatures held a combination of longer chained alkanes, of C18 and longer. However, the last temperature converted 100% of the feedgas into methane and CO2. The product selectivity to CH4 and CO2 posed a problem with the Fe-SWNTs catalyst, where in all temperatures the selectivity exceeded 80%. Ni-SWNTs (nickellocene assisted SWNTs) yielded slightly better results with a higher selectivity to C2-C7, but no selectivity to longer chained hydrocarbons. Co-SWNTs (cobaltocene assisted SWNTs) tested under the same parameters yielded similar results as the Fe-SWNTs, with a very high selectivity to CH4 and CO2. Only at temperatures of 300 and 250°C were there any selectivity to compounds other than CH4 and CO2, but less than 10% selectivity to those alkanes (C2+). The final experiment consisted of a catalyst prepared from a feed solution containing a mixture of ferrocene and nickellocene. The Fe+Ni-SWNT catalyst underwent the same conditions as the other SWNT catalysts, this combination yielded favorable results with over 98% conversion of syngas over all temperatures and a high selectivity to shorter chain length hydrocarbons, namely alkanes of chain lengths between C2 and C7. Although the higher temperatures did show a selectivity to methane (roughly 45%), the CO2 selectivity was rather low, below 10% (except at 450°C, which pushed 20%).
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Donado, Sainz de la Maza Esther. "Cobalt supported on mesoporous silicas for the Fischer-Tropsch synthesis." Thesis, KTH, Skolan för kemivetenskap (CHE), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-158473.
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This thesis deals with the study of several catalysts for the Fischer-Tropsch synthesis in the Biomass-To-Liquid process. In this work two groups of catalysts were tested. On the one hand, two series of catalysts with cobalt loadings of 6 and 12 wt% over SiO2 and some of them containing 5wt% of TiO2 were tested. One the other hand, other two series of mesoporous short channel SBA-15, all of them with cobalt loadings of 12wt% and some with 5wt% of titania. The first series was supported on SBA-15 DeWitte and the second one on SBA-15 Martinez. On the one hand, the influence of water addition to the feed, titania content and cobalt loading to the catalyst and was studied, as well as the consequences of a GHSV. The FT reaction was carried out along 5 periods of 24 hours each, in which conditions such as feed and water content were modified, enabling the study of these parameters. It was found that water provokes an increase of the CO conversion and has a positive kinetic effect on the rate to hydrocarbons. However, this fact reaction is followed by a quick deactivation, enhanced by high water partial pressures. Most of that deactivation is irreversible since it is not completely recovered after water removal. On the other hand, differences between the supports were studied. Some SBA-15 supported catalysts show CO diffusion limitations at longer channel lengths than what applies for conventional 3D porous supports. Titania grafting increases the rate to hydrocarbons, showing positive results for FT catalysts development.
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Kraum, Martin. "Fischer-Tropsch synthesis on supported cobalt based Catalysts Influence of various preparation methods and supports on catalyst activity and chain growth probability /." [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=959085181.
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Zhuang, Youqi. "The performance of structured cobalt catalysts in Fischer-Tropsch synthesis." Doctoral thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/5381.
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Cobalt is the preferred catalyst metal for the production of clean burning, high cetane number diesel fuel from synthesis gas using the Fischer-Tropsch synthesis. Hence, increasing C5+ selectivity of cobalt catalysts is one of the hot topics in Fischer-Tropsch synthesis. Internal mass transport limitation may affect C5+ selectivity. It was concluded that mild transport limitation is required for maximum C5+ selectivity. Mild transport limitation also increases the catalyst activity, since the reported Fischer- Tropsch rate of reaction has a negative dependency on CO partial pressure. The metal distribution within catalyst pellets may modify product selectivity by changing the local metal density and the diffusion path length. However, current catalyst preparation methods limit metal distribution in transition metal catalysts. The aim of this study is to explore a possible catalyst synthesis route for egg-shell, egg-yolk and egg-white type of cobalt catalyst pellets. The establishment of the nonuniform cobalt catalyst synthesis method will provide an observational evaluation technique for the investigation of the effect of intra-pellet metal distribution on the activity and product selectivity of the Fischer-Tropsch synthesis. The non-uniform catalyst synthesis method utilises the hydrophobic nature of the silica pellet. Egg-shell, egg-yolk and egg-white type of cobalt catalyst with sharp metal enriched boundary were synthesized. The intra-pellet cobalt distribution, metal particle size, metal loading, metal surface area and catalyst reducibility were characterised. The performance of these non-uniform catalysts was tested in a modified slurry type reactor. Catalyst pellets were kept in mesh-wire baskets which were mounted inside a slurry reactor, and tested in the absence of external mass transport limitation. The Fischer-Tropsch activity was recorded and modelled using a reaction-diffusion pellet inside a continuous stirred tank reactor model. The product selectivity were analysed with an offline GC. The Fischer-Tropsch activity is strongly dependent on the intra-pellet metal distribution. The egg-shell type of catalyst outperforms the uniform, egg-yolk and eggwhite type of catalyst, in terms of activity, under the influence of internal mass transport limitation. The intra-pellet distribution alters the reactant concentration in the pellet as well as intra-pellet H2/CO ratio. The reaction-diffusion path length was identified to be a suitable parameter for product selectivity. An increase in the reaction-diffusion path results in an increase in -olefins re-adsorption, a decrease in olefin content and an increase branched product compounds. Secondary chain growth is not favoured under internal mass transport limitation.
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Finch, Karol Paula. "Synthesis, characterisation and reactivity studies of μ(α, ω)-alkanediyl complexes of ruthenium, iron and cobalt." Master's thesis, University of Cape Town, 1988. http://hdl.handle.net/11427/21938.
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The new series of μ(α, ω)-alkanediyl compounds of ruthenium, [CpRu(CO)₂]₂[μ-(CH₂)ₙ], where n=5-10, have been prepared from Na[CpRu(CO)₂] and the corresponding diiodoalkane. These compounds, which are stable crystalline solids at ambient temperature, have been fully characterised by microanalysis, infrared, ¹H and ¹³C NMR spectroscopy, melting point and mass spectrometry. The new heterodinuclear complex [Cp(CO)₂Fe(CH₂)₄Ru(CO)₂Cp] has been synthesised by the reaction of [CpFe(CO)₂(CH₂)₄I] with Na[CpRu(CO)₂] and characterised by all the above mentioned techniques.
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Mena, Subiranas Alba. "Combining Fischer-Tropsch Synthesis (FTS) and Hydrocarbon Reactions in one Reactor." [S.l. : s.n.], 2008. http://digbib.ubka.uni-karlsruhe.de/volltexte/1000010077.
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Rose, Amadeus [Verfasser]. "Nano-carbon supported cobalt catalysts in Fischer-Tropsch synthesis / Amadeus Rose." Aachen : Shaker, 2014. http://d-nb.info/105157269X/34.
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Güttel, Robert [Verfasser]. "Monolith loop reactors for Fischer-Tropsch synthesis / submitted by Robert Güttel." [Clausthal-Zellerfeld] : [Univ.-Bibliothek], 2009. http://d-nb.info/993616569/34.
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Zhao, Yanjun. "On the investigation of alcohol synthesis via the Fischer Tropsch reaction." Thesis, Cardiff University, 2007. http://orca.cf.ac.uk/55862/.
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The Fischer Tropsch (FT) reaction is hydrogenation of carbon oxides (mainly carbon monoxide) to produce hydrocarbons and alcohols. The produced alcohols can be used as substitutes to motor fuel or as fuel additives to enhance the octane number. The use of alcohols significantly reduces the environment related pollution. This thesis was aimed to investigate the alcohol synthesis via the FT reaction. Cobalt molybdenum based catalyst and cobalt copper based mixed oxide catalyst are two patented catalyst systems for alcohol synthesis. This study investigated the preparation and evaluation of these two catalyst systems. The highest activity (30% CO conversion) and alcohol yield (methanol: 8% higher alcohols: 13%) was obtained with an operation condition of 580 K, 75 bar, GHSV = 1225 h-1 and syngas ratio of 2 for cobalt molybdenum based catalyst. Carbon monoxide hydrogenation to synthesize alcohol was also investigated over gold containing catalyst. When ZnO was used as a support, it was found that the addition of gold could shift the alcohol distribution towards higher alcohol side. The carbon monoxide and hydrogen used for the FT reaction is mainly generated by steam reforming reaction. This thesis investigated the possibility of combining the steam reforming reaction and the FT reaction together. Ruthenium supported catalysts were investigated for this purpose. The obtained results demonstrate that both steam reforming and the FT alcohol synthesis can be performed over the same catalyst in the same reactor.
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Iqbal, Sarwat. "Investigation of Fischer-Tropsch reaction for synthesis of hydrocarbons and alcohols." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/54875/.
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Fischer Tropsch (FT) technology as a source of alternate fuels is unique. The FT products are of excellent quality and their environmental properties are valuable in increasing drive towards cleaner fuels. There was surge of interest in FT in the thirties and fifties (during the Second World War) and now again in last couple of years. Fischer Tropsch technology has a disadvantage of broad product spectrum. There is strong requirement of improvement in the optimization of reaction in order to get a maximum yield of high value commercial products, mainly high value molecular weight products, alcohols and short chain hydrocarbons. Most of the investigations reported in this thesis have dealt with study and possible modifications in the preparation and reaction conditions of previously studied CoMnOx catalyst. Co-precipitation method for preparation of this catalyst has been studied in detail. Precipitation by variable pH has been found to be better than constant pH. pH, ageing time of precipitates and temperature of precipitation mixture are very important parameters which affect the selectivity pattern of products. This selectivity pattern was found to be further influenced by reaction temperature and pressure during CO hydrogenation reaction. An improvement in the selectivities for CO hydrogenation reaction has been developed using a modified co-precipitated Co/Mn oxide catalyst. This modification was achieved by using two different metal promoters, i.e., Potassium and ruthenium. Addition of these promoters has influenced the catalytic properties in a variety of ways as was observed from characterization and reaction results. Addition of small quantity of potassium (0.15%), and ruthenium (0.1%) promoters shifted the product spectrum to long chain hydrocarbons along with decrease in methane selectivity. Further improvements in catalytic activity and selectivity were made by addition of two different types of activated carbons (wood and peat shell) into Co/Mn catalyst. Co and Mn impregnated on wood peat carbon were found to be highly selective for high molecular weight hydrocarbons along with low selectivity of CO2 compared with pure CoMnOx catalyst. An increase in concentration of metals with these carbons showed an increase in selectivity of CO 2. One particular catalyst system of iron and manganese was studied with peat and wood carbons and was found to be highly selective for CO 2 formation. Alcohols, an important product of FT reaction are a good substitute to motor fuel which can enhance the octane number and can reduce the environmental pollution. Cobalt molybdenum sulphide is a patented catalyst system for alcohols synthesis. Present study has investigated the influence of transition metal promoters on selectivity pattern of this catalyst. Ti, Ni and Zr metals have been used as promoters. Addition of Ni and Ti into C0M0S2 have shown good catalytic activity but the major product was CO2. Zr addition has shown less CO2 and more hydrocarbons. Pure C0M0S2 catalyst was found to be better for synthesis of higher alcohols.
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Gautam, Jitendra. "PARAMETRIC STUDY OF FISCHER-TROPSCH SYNTHESIS IN SUPERCRITICAL PHASE CARBON DIOXIDE." OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/340.
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AN ABSTRACT OF THE THESIS OF JITENDRA GAUTAM, for the Master of Science degree in MECHANICAL ENGINEERING AND ENERGY PROCESSES, presented on JUNE 18TH 2010, at Southern Illinois University Carbondale. TITLE: PARAMETRIC STUDY OF FISCHER-TROPSCH SYNTHESIS IN SUPERCRITICAL PHASE CARBON DIOXIDE MAJOR PROFESSOR: Dr. Kanchan Mondal The results from studies on Fischer Tropsch synthesis wherein syngas was dissolved in CO2 are presented. The syngas generally used was typical of that obtained from coal gasification, i.e. CO:H2 of one. Under these conditions Co-based catalysts without any water gas shift catalyst does not perform well while Fe - based catalysts have been found to be useful. However, the Fe based catalysts have a propensity towards CO2 selectivity via the primary FT reaction, Boudouard reaction and the water gas shift reaction. The use of CO2 as a solvent was found to suppress the CO2 and CH4 selectivity while enhancing the hydrocarbon selectivity and CO conversion when FT synthesis was conducted using coal derived syngas on Fe-Zn-K catalysts. The effects were found to be significantly pronounced at pressures higher than or equal to 1200 psig. It should be noted that CO2 is supercritical at pressures higher than 1070 psig and 31.4 oC. The effect of CO2 partial pressure, reactor pressure, reaction temperature, catalyst loading and H2:CO ratio in syngas on the liquid product distribution was evaluated. Some of the notable findings include product tenability by varying temperature and pressure as well as varying the CO2 partial pressure and the syngas composition. Increasing the reactor pressure was found to favor longer chain growth. In addition, it was noted that the ratio between CO2:syngas in the reaction mixture is an important factor in the liquid product distribution. A higher value of the ratio is seen to favor hydrocarbon synthesis, while a lower value of the ratio favors oxygenate production particularly pentanols and butanols. In addition, the data on the once through fractionation of the products utilizing the solubilities in supercritical CO2 and pressure tuning were encouraging. It was found that the products can be easily fractionated into narrow carbon chain length distributions downstream of the reactor by simply reducing the pressures in each collection vessel. It was generally observed that oxygenates and higher n-alkanes were collected in the higher pressure trap and lower hydrocarbons in the subsequent lower pressure traps.
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Davies, Imaad. "Development of a Kinetic Model for Low Temperature Fischer-Tropsch Synthesis." Master's thesis, Faculty of Engineering and the Built Environment, 2021. http://hdl.handle.net/11427/33692.
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Globally, there is a need to replace our dependence on fossil fuels as the main source of energy. This requires a shift towards renewable and sustainable alternatives. The well-established FischerTropsch (FT) synthesis is a potential process route to produce liquid fuels and speciality chemicals and address this challenge. FT synthesis is a polymerisation reaction in which syngas, a mixture of CO and H2, is converted to hydrocarbon products ranging from methane to wax when low temperature conditions are used. Subsequent product upgrading steps allow high quality liquid fuels to be obtained which are clean burning. This will help to mitigate the impact of human activity on the environment. The versatility of this process route is attributed to the ability of syngas to be generated from any carbon-containing feed such as coal, natural gas or biomass. The latter is attractive to enable a shift to a more sustainable way of living. Particularly for biomass-to-liquid plants, the high cost of syngas generation means that FT synthesis should use syngas as efficiently as possible. This requires an effective description of the FT reaction kinetics. This study therefore focuses on the development of a kinetic model for low temperature FT (LTFT) synthesis to improve understanding of the reaction behaviour and aid in the development of a biomass-to-liquid process route. Although the kinetics of the FT reactions under the low temperature conditions of 180-260 ◦C and 20-30 bar(a) have been extensively studied, the challenge to kinetic model development is the large number of possible reaction products. A common simplification is to consider the formation of the main products only, which are linear n-paraffins and 1-olefins. The polymerisation character of FT synthesis means that its product distribution could ideally be described using models based on probability theory. Deviations from probability theory distribution, however, occur especially at the conditions of LTFT synthesis. These deviations are a high methane yield, low ethene yield and the change from mainly 1-olefins at low carbon number to mainly n-paraffins at high carbon number. Comprehensive kinetic models in literature focus on finding a kinetic explanation for these deviations. These kinetic models, however, cannot easily be used with few being extended to include the formation of products of higher carbon number. An aspect ignored in current kinetic model development is that FT synthesis shares many aspects of an equilibrium-controlled process. This is since CO hydrogenation which leads to monomer formation is the rate-determining step for the FT reactions. Consequently, the rate of chain growth is rapid in comparison. This leads to the distribution of n-paraffins and 1-olefins being controlled by equilibrium. By modelling FT synthesis as an equilibrium-controlled process, the kinetic model formulation could be simplified, consist of fewer rate expressions and contain the minimum number of model parameters without compromising on prediction quality. At the conditions of LTFT synthesis, both the vapour and liquid phases exist during reaction. The formation of liquid and its effect on the kinetics of FT synthesis has, however, often been neglected with most kinetic models considering the vapour phase only. This is despite of the effect that liquid formation has on product selectivity. The kinetic model developed in this thesis therefore aimed to combine the interaction between chemical equilibrium, kinetics and liquid formation and account for the formation of products of high carbon number. This will assist in providing a comprehensive description of the observed FT reaction behaviour in a simple and tractable manner. A pre-requisite to kinetic model development is the creation of a physical property database for nparaffins and 1-olefins which is extendable to high carbon numbers. This is since only the physical properties of low carbon number n-paraffins and 1-olefins are known because they are common in most industrial processes. For chemical and phase equilibrium calculations, the critical and ideal gas properties needed to be estimated. The Constantinou Gani group contribution method, with modification to the group contributions, proved to be an effective strategy to predict the physical property data for low carbon number n-paraffins and 1-olefins. The correlations developed should therefore provide an adequate approximation of the properties of their higher carbon number relatives. To model the phase behaviour of FT synthesis, the Peng-Robinson equation of state is used. Modifications were made to the alpha function of this equation of state to ensure it remained valid when the describing the behaviour of heavy hydrocarbons. The kinetic model development which relies on the equilibrium aspects of the reactions involved to describe the formation of n-paraffins and 1-olefins. The reaction pathway implemented is based on the alkyl mechanism and assumes that FT synthesis can be viewed as a methylene (CH2) polymerisation. In addition, the water gas shift (WGS) reaction is also considered. Methylene is taken as the monomer and enabled the reactions in FT synthesis to be represented using an equilibrium approach. Each rate expression is formulated as an equilibrium-controlled process, using species activity as the kinetic driving force. This proved to be an effective strategy to account for the observed reaction behaviour, namely a high methane yield, low ethene yield and the change from mainly 1-olefins at low carbon number to mainly n-paraffins at higher carbon number. This approach also allowed the model to effectively capture changes in product selectivity and the product distribution as a function of process conditions (CO conversion, temperature, pressure and H2/CO feed ratio). These changes could be explained by considering the equilibrium aspects of the reactions involved. The model only requires six adjustable parameters i.e. rate constants. An important part of model development is knowing how the model rate constants determine the model output. This provides insight regarding which rate constants can be determined from the regression of data. For this purpose, a sensitivity analysis was performed on the selectivity to C1, C2, C3, C4, C5+ and CO2 as a function of CO conversion. This analysis revealed that CO hydrogenation is rate-determining which agrees with findings in literature. This analysis also revealed that model rate constants are cross-correlated when product selectivity as a function of CO conversion data is studied. This means that meaningful estimation of all rate constants using data of this form is not possible. However, it was found that when product distribution data at constant CO conversion is used instead, then meaningful estimates of the rate constants could be determined. This is if CO conversion is below 60%. Over this CO conversion range, the product distribution is independent of the WGS reaction. The WGS rate constant should thus be approximated using data in literature. As such, five rate constants need to be determined from the regression of product distribution data. Model validation occurred by regression of product distribution data at constant CO conversion. Emphasis was placed on the ability of the model to predict changes in the product distribution with temperature. A quantitative measure of the model fit is the precision with which the rate constants were estimated. A good fit to experimental product distributions in both fixed-bed and slurry reactors is obtained. The kinetic model has therefore been shown to be independent of reactor type. The good fit to data is quantified by the small error in the estimated rate constants, particularly for CO conversions up to approximately 30%. Higher variability in the estimated rate constants was obtained for higher CO conversions. This emphasised the importance of estimating rate constants at conditions where the product distribution is most sensitive. The temperaturedependence of the rate constant could be described by an Arrhenius expression. The effect of liquid formation on the kinetic behaviour of FT synthesis was modelled by assuming that the vapour and liquid phases are in equilibrium. The choice of species activity as the kinetic driving force allowed the kinetic model to be applied in both the vapour and liquid phases. Although the system was mainly in the vapour phase, liquid formation alters selectivity. Single-phase simulations are valid up to a CO conversion of 20% and predict a higher selectivity to products of carbon number in the diesel product grade (C10-C20). Between a CO conversion of 20-90%, it becomes essential to account for liquid formation to ensure that the favourable selectivity to wax products (C21+) in FT synthesis is adequately captured. The predictions of the single- and two-phase simulations were assessed by comparison to the wax product from LTFT reactors in Sasol processes. Both simulations were found to be useful in describing these wax product distributions. The kinetic model developed in this thesis therefore effectively describes the behaviour of FT synthesis. The ability of the model to predict changes in product selectivity and the product distribution as a function of process conditions will make it a powerful tool involved in the design of FT processes. It is recommended that the approach taken to develop the model be used to study the kinetics of other gas-to-liquid processes, for reactor design and flowsheet development.
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Whiting, Gary Ken. "Development of a microreactor system for unsteady-state Fischer- Tropsch synthesis." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/76086.
Full textAbstract:
Vibrofluidized microreactor systems have been developed for studies of unsteady-state Fischer-Tropsch synthesis. This development is aimed at preventing carbon deposition on a fused-iron catalyst in a novel reactor called the “heat-tray.” This reactor involves a supernatant gas flowing over a shallow fluidized bed of catalyst particles. Three systems were built: (1) a vibrofluidized-bed microreactor system for obtaining baseline carbon deposition infonnation under industrially important reaction conditions; (2) a sliding-plug vibrofluidized-bed microreactor system for rapid switching of feed gases in the F-T synthesis; and (3) a cold-flow microreactor model for studying the gas mixing characteristics of the sliding-plug vibrofluidized-bed microreactor.
The results show that catalyst defluidization occurred under steady-state synthesis conditions below 395°C using a feed gas of H₂/CO ratio of 2:1 or less. Above 395°C, the probability of hydrocarbon chain growth (α) on the fused-iron catalyst was low enough (α < 0.50) to prevent accumulation of high-molecular-weight species that cause defluidization. Carbon deposition was rapid above 395°C when a feed gas of H₂/CO ratio of 2:1 or less was used.
Spent catalyst fractions in the form of free-flowing catalyst and "bugdust" were quantitatively analyzed for carbon and iron. Mössbauer spectroscopic analysis of free-flowing catalyst showed mainly Hägg carbide (x-Fe₅C₂) and magnetite (Fe₃O₄) with a smaller fraction present as α-Fe. Scanning electron microscopic analysis of the bugdust revealed a mass of highly porous, fine particles with a high carbon content (18-30 wt%).
Cold-flow microreactor model studies show that rapid (on the order of seconds), quantitative switching of feed gases over a vibrofluidized-bed of catalyst could be achieved. Vibrofluidization of the catalyst bed induced little backmixing of feed gas over the investigated flow-rate range of 417 to 1650 actual mm³/s. Further, cold-flow microreactor model studies showed intense solid mixing when a -150+300 µ bed of fused-iron catalyst was vibrofluidized at 24 cycles per second with a peak-to-peak amplitude of 4 mm.
The development of this microreactor system has provided an easy way of accurately determining integral fluid-bed kinetics in a laboratory reactor. Further, the unique ability of the microreactor system to rapidly switch feed gases over an intensely-mixed solid has important applications in chemical kinetics and reaction engineering.Ph. D.
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Bungane, Ntombovuyo. "Ruthenium and osmium complexes as catalyst precursors for Fischer-Tropsch synthesis." Master's thesis, University of Cape Town, 2004. http://hdl.handle.net/11427/6296.
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Includes bibliographical references (leaves 63-65).Ruthenium complexes of several types have been synthesized, supported on silica and their activity in CO hydrogenation was investigated in order to determine the cluster size of surface Ru atoms required for the formation of hydrocarbons. Previous studies have shown that more than one metallic site is needed for the Fischer-Tropsch synthesis.
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Cairns, Pete. "Oxygenates in iron Fischer-Tropsch synthesis : is copper a selectivity promoter?" Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/5361.
Full textAbstract:
Includes synopsis.Includes bibliographical references (p. 188-197).
The Fischer-Tropsch synthesis is regarded as a stepwise polymerisation reaction between adsorbed hydrogen, carbon monoxide and monomers formed from them. Commercially, a supported precipitated iron catalyst promoted with small amounts of potassium and copper is one of the catalysts used in this reaction. Precipitated iron catalysts are chemically promoted with potassium in order to enhance the product selectivity, while copper is added as a reduction promoter which increases the reduction rate and decreases the reduction temperature of the iron catalyst. The effect of copper on the product selectivity however, remains unclear. This study falls into three distinct categories: firstly the preparation of co-precipitated iron-copper catalysts of varying copper loading and the characterisation of the calcined, reduced and spent catalysts; secondly Fischer-Tropsch synthesis in both fixed-bed and Berty reactors to investigate the effects on product selectivity in regard to copper, and finally the co-feeding of C8 oxygenates, over a pure iron, and an iron catalyst promoted with 50 wt% copper, to investigate the mechanism and pathways of interaction. Co-precipitated iron-copper catalysts were prepared from their nitrates andsubsequently promoted with potassium. Characterisation of these catalysts showedthat the addition of copper formed small (x-ray amorphous) iron crystallites that decreased in size with copper loading. It was also found that the added potassium had a higher affinity for the iron than the copper. Upon reduction the iron crystallites agglomerated to a constant size while the size of the copper crystallites increased with copper loading. Examination of the spent catalysts showed constant ratios of Hägg carbide to magnetite but a decrease in the size of the iron carbide crystallites with increased copper promotion.
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Walsh, Richard. "Fischer-Tropsch synthesis over SiO2, ZnO and MnO supported cobalt catalysts." Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/17953.
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Includes bibliography.Silica is well known as a support for cobalt supported Fischer-Tropsch catalysts. Silica has a high surface area with an amorphous structure that promotes dispersion of the active cobalt phase over the support surface. This dispersion is vital in terms of catalyst performance and derives from the strength of interaction between the cobalt and the support. However, the stronger the metal support interaction, the greater is the loss of active cobalt through formation of cobalt support species that are hard to reduce. Consequently ZnO and MnO were evaluated in comparison to Si02 as supports for cobalt supported Fischer-Tropsch catalysts. The aim of the study was to characterise the interaction between cobalt and the three supports (Si02, ZnO and MnO) in terms of the cobalt reducibility as visualised using TPR, exposed cobalt surface area and cobalt dispersion as evaluated using hydrogen chemisorption, and catalytic performance under Fischer-Tropsch synthesis conditions.
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Nguyen, Tuan Huy Chemical Sciences & Engineering Faculty of Engineering UNSW. "Semiconductor oxide supported Mo and Mo-W carbide catalysts for Fischer-Tropsch synthesis." Awarded by:University of New South Wales. School of Chemical Sciences and Engineering, 2006. http://handle.unsw.edu.au/1959.4/26969.
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Fischer-Tropsch synthesis reaction to produce sulphur free hydrocarbons has enjoyed a resurgent in interests due to increases in world oil prices. In this work, the suitability of Mo and Mo-W carbides has been investigated as a possible cost-effective alternative to noble metals in Fischer-Tropsch synthesis. The molybdenum and tungsten monometallic and bimetallic carbides were prepared through precipitation from homogeneous solution to the sulphide followed by carburization with a mixture of propane and hydrogen to produce the resulting metal carbide. A 23 factorial design strategy was employed to investigate the effect of three carburizing variables, namely, time, temperature and gas ratio on the resulting catalyst. In particular, the effect of supports was also examined through four common semiconductor oxide supports, namely: Al2O3, SiO2, TiO2 and ZrO2. Thermogravimetric analysis of the carburization reactions showed that the conversion from metal sulphide to the metal carbides is a multistep process producing different phases of carbides, namely ??-MoC1-x, ??-Mo2C, ?? -WC1-x and ??-W2C, depending on heating rate and temperature. The rate determining step of the carburising reaction is the diffusion of carbon atoms into the metal matrix, hence giving relatively low activation energy values. Statistical analysis of the factorial design revealed that all three carburizing variables affect the final physiochemical makeup of the catalyst. SEM analysis showed that the carbides are well dispersed on the surface of the support and catalyst particles produced are nanoparticles in the range of 25 to 220 nm depending on the support. Fischer-Tropsch activity test showed that monometallic molybdenum carbide is active under Fischer-Tropsch conditions while tungsten carbide is inactive for the conditions studied in this project. However, bimetallic carbide catalyst, consisting of the two mentioned metals gave overall higher reaction rates and decreased methane selectivity. Steady state analysis revealed that there are two active sites on the surface of molybdenum carbide catalyst resulting in two chain growth propagation values when analysed via the Anderson-Schulz-Flory kinetics. Overall, ZrO2 support appeared to be the most suitable support followed by SiO2, TiO2 and Al2O3. Finally, kinetic modelling of data showed that methanation and higher hydrocarbons formation path occurs via combination of the oxygenated intermediate and Eley-Rideal mechanism.
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Lee, Yong Joon Chemical Sciences & Engineering Faculty of Engineering UNSW. "Synthesis, characterisation, and evaluation of supported cobalt molybdenum nitride for Fischer-Tropsch reaction." Publisher:University of New South Wales. Chemical Sciences & Engineering, 2008. http://handle.unsw.edu.au/1959.4/41487.
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Fischer-Tropsch Synthesis (FTS) is known as the most practical way to convert natural gas to hydrocarbon products including synthetic fuel depending on the catalysts and operating conditions. Australia has 25% of world's natural gas resources hence Australia's crude oil dependency can be reduced extensively by developing catalysts that will facilitate the technique of converting natural gas to synthetic fuel. Molybdenum nitride has been employed in this study for FTS because of its superior mechanical strength, stability, exceptional resistance to carbon deposition & suifur poisoning. In particular, molybdenum nitride is endowed with similar electronic properties to those of noble metals. Other transition metal nitrides such as Co nitride and Co-Mo nitride were also investigated in this study. The physicochemical attributes of nitride catalysts were examined by BET surface area, particle dispersion, acid site strength & concentration, and surface elemental composition. Gas to solid nitridation kinetic was thermogravimetrically monitored. CO hydrogenation activity was measured in a fixed bed reactor using various syngas compositions and temperatures at atmospheric pressure. The effect of nitridation conditions on catalytic properties of nitrides was investigated via 23 factorial design. It has revealed that nitridation parameters; temperature, nitriding gas composition (H2:NH3) and nitridation reaction time were all significantly influencing catalyst properties. The optimal nitridation condition was 973 K, H2:NH3=1: 1, and 4 hours of nitriding time which gave higher alkene selectivity. 20 wt% M02N/Ah03 was found to be the better FT catalyst compare to catalysts with lower Mo loading and other inorganic oxide supports. Nitridation kinetic studied by thermogravimetric analysis showed that successful nitridation of transition metal oxide precursor was dependent of nitridation temperature and hydrogen concentration. Co-Mo nitride has several forms of nitride species, COS.47N, C03M03N, MoN, and Mo2N. It was shown that COS.47N was the most active component favouring the CO hydrogenation rate and alkene selectivity. Mechanistically-based kinetic models suggested that methanation over Co nitride occurs mainly via surface carbon while surface oxygenated intermediates were accountable for methanation over Co-Mo nitride and Mo nitride.
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Benoit, Jeremiah. "SUPERCRITICAL PHASE FISCHER-TROPSCH SYNTHESIS INHIBITION OF CO2 SELECTIVITY FOR ENHANCED HYDROCARBON PRODUCTION." OpenSIUC, 2008. https://opensiuc.lib.siu.edu/theses/485.
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ABSTRACT This thesis presents the results from research conducted on Fischer-Tropsch synthesis (FTS) in supercritical CO2 from syngas (H2:CO =1:1) typically produced from coal gasification and using a Fe-Zn-K catalyst. Experiments were conducted with syngas alone at different pressures (200 psi - 1050 psi) and temperatures (275, 350 and 375 oC). Experiments were also conducted with a syngas pressure of 200 psi and at different partial pressures of an inert diluent (N2) such that the total pressure varied from 200 psi to 1050 psi. Finally, experiments were conducted with CO2 as a diluent and at a syngas pressure of 200 psi. The CO2 partial pressure was increased from 0 psi to 1400 psi (non critical to supercritical conditions). The data show an enhancement in the hydrocarbon selectivity and reduction in the parasitic loss of carbon efficiency due to CO2 formation along with significant improvement in the conversion rates. The experiments were conducted in a unique reactor setup that can conduct gas phase or supercritical phase FT synthesis in both batch or flow modes. The use of the supercritical CO2 (ScCO2) inhibited both CH4 and CO2 selectivities while enhancing the rates of synthesis. In addition, the use of supercritical CO2 is expected to prolong the life of the catalyst presumably by removing the heat of reaction from the catalyst's surface and solubilizing the waxes that tend to deposit on the surface. Although not within the scope of this thesis, the products from such a reactor system can be easily separated without the need of an additional unit process simply by tuning the pressure and temperature. The product spectrum and the selectivities for the different products are presented for each set of experiments. The effects of process parameters such as temperature, pressure, N2 partial pressure, and CO2 partial pressure on the product spectrum are also discussed. The clear increase in CO conversion at H2:CO ratio of 1:1 in supercritical phase as compared to gas phase reaction, the decrease in CO2 and CH4 selectivity, and an overall shift in the product distribution towards higher hydrocarbons have been demonstrated. Thus the use of supercritical CO2 has the potential through the FT process to convert coal to liquid fuels using Fe based catalysts, especially since the reactions can be conducted in a two phase regime without losing the benefits of the 3-phase slurry reactor systems
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BRAGANCA, LAURINDA FATIMA DA FONSECA PEREIRA GUIMARAES. "SYNTHESIS AND CHARACTERIZATION OF CO-FE NANOCRYSTALS SUPPORTED ON MESOPOROUS SILICAS FOR THE FISCHER-TROPSCH SYNTHESIS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2010. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=15921@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRONeste trabalho foram sintetizadas amostras bimetálicas de cobalto e ferro suportadas em sílicas mesoporosas do tipo SBA-15 e HMS. A preparação das mesmas ocorreu pelo método de impregnação incipiente do ponto úmido com soluções aquosas de nitratos de Co e Fe para obtenção de amostras com 25% p/p total de metal. Para estudos de efeitos comparativos das diversas propriedades, amostras monometálicas de Co ou Fe foram também preparadas com o mesmo teor metálico. Para investigar o efeito de diferentes direcionadores de estrutura, duas séries da sílica mesoporosa HMS foram preparadas utilizando dois tipos de direcionadores: dodecilamina (DDA) e tetradecilamina (TDA). As amostras foram caracterizadas por medidas de fisissorção de N(2), análise de difração de Raios-X (DRX), redução com temperatura programada (RTP), microscopia eletrônica de transmissão (TEM), quimissorção de H(2) e espectroscopia fotoeletrônica de raios-X (XPS). A quantidade de metal incorporado foi estimada por espectroscopia de absorção atômica (EAA). Os suportes foram também caracterizados por análise diferencial termogravimétrica (ATG/ATD). As curvas ATG evidenciaram que os direcionadores de estrutura foram, em grande parte, removidos até 700 K. As propriedades de textura mostraram que após a introdução metálica no suporte SBA-15, a área específica, o volume de poros e o diâmetro de poro decresceram em menor extensão para a amostra bimetálica em relação às monometálicas. As análises de DRX detectaram a formação das fases de Co(3)O(4) e CoFe(2)O(4) para todas as amostras bimetálicas; sendo que para a amostra de Co-Fe/HMS (TDA), a fase a-Fe(2)O(3) foi também indicada. A presença do suporte HMS (TDA) resultou na formação de fases cristalitas de maiores dimensões. Os valores das espessuras de parede para os suportes do tipo HMS foram maiores em relação aos encontrados na literatura, sugerindo a formação de materiais mais estáveis. Os perfis de RTP foram similares entre as amostras monometálicas e bimetálicas, entretanto, maiores temperaturas de redução do óxido de cobalto na amostra bimetálica foi indicada em relação às amostras monometálicas de cobalto, no suporte HMS (TDA). Uma interação metal-suporte mais forte foi evidenciada para a amostra Co-Fe/SBA-15. As medidas de quimissorção de H(2) indicaram valores das dispersões metálicas maiores para as amostras bimetálicas em comparação as monometálicas de ferro e menores em relação às monometálicas de cobalto. A partir das micrografias obtidas por MET, foi observada uma menor formação (percentual) de aglomerados para a amostra de Co-Fe/SBA-15 em relação à de Co-Fe/HMS (DDA). O espectro Co2p resultante da análise de XPS, para a amostra bimetálica de Co-Fe/HMS (DDA) indicou a presença de Co(3)O(4). O catalisador de Co-Fe/HMS (DDA) apresentou maiores seletividades para C(5+) e álcoois em relação ao catalisador Fe/HMS (DDA) na síntese de Fischer-Tropsch. O parâmetro de probabilidade de crescimento da cadeia (a) foi maior para o catalisador bimetálico Co-Fe/HMS (DDA) em comparação ao catalisador Co-Fe/SBA-15. Ambos os catalisadores bimetálicos exibiram uma seletividade (%) maior para a fração de leves, C2-C4.
In this work, cobalt and iron bimetallic samples supported on SBA-15 or HMS mesoporous sílicas were prepared by incipient wetness impregnation. Cobalt nitrate and iron salts were used to obtain samples containing 25 wt% total of metal content. Also, a series of supported monometallic cobalt or iron samples were synthesized, with the same metal loading, and compared to bimetallic ones. In order, to investigate the effect of different templates, a series of HMS sílicas have been prepared using two types of structure direction: dodecylamine (DDA) and tetradecylamine (TDA). The samples were cheracterized by N(2)-physisorption, X-ray diffraction (XRD), temperature programmed reduction (TPR), transmission electron microscopy (TEM), H(2) chemisorption and X-ray photoelectron spectroscopy (XPS) analysis. The amount of incorporated metal was estimated by atomic absorption spectroscopy (AAS). The supports were, also, characterized by thermogravimetric (TGA), as well as differential thermal (DTA) analyses. The TGA/DTA curves showed that the templates were mainly removed until 700 K. The textural properties revealed that after metal introduction to SBA-15 support, specific area, pore volume and pore diameter decreased in a lesser extension for the bimetallic sample compared to monometallic ones. XRD measurements detected the formation of Co(3)O(4) and CoFe(2)O(4) phases for all bimetallic samples. For Co-Fe/HMS (TDA) sample, the a-Fe(2)O(3) phase formation and a higher Co(3)O(4)/CoFe(2)O(4) crystallite sizes were also observed. The wall thickness valour for HMS supports was higher than previously reported values, suggesting more stable materials. The TPR profiles indicated similar behavior between bimetallic and monometallic samples. In case of cobalt oxide on bimetallic sample, higher reduction temperatures were indicated compared to monometallic ones for HMS (TDA) support. A higher interaction metal-support was showed for Co-Fe/SBA- 15. According to hydrogen chemisorption, the bimetallic samples dispersions were higher than iron monometallic and lower than cobalt monometallic samples. From TEM microphotografs, it was observed a lesser fraction of agglomerates to Co-Fe/SBA-15 than Co-Fe/HMS (DDA) sample. XPS spectrum of Co2p region indicated the presence of Co(3)O(4) for the bimetallic sample, Co-Fe/HMS (DDA). The Fe-Co/HMS (DDA) bimetallic catalyst showed higher C(5+) and alcohols selectivities than Fe/HMS (DDA) on the Fischer-Tropsch reaction. Also, the bimetallic cobalt and iron based catalyst supported on HMS (DDA) recorded a higher value for the chain growth parameter (a) than Co-Fe/SBA-15. Both bimetallic catalysts exhibited highter selectivities (%) for lighter fractions, C2-C4.
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Almkhelfe, Haider H. "Scalable carbon nanotube growth and design of efficient catalysts for Fischer-Tropsch synthesis." Diss., Kansas State University, 2017. http://hdl.handle.net/2097/38213.
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Doctor of PhilosophyDepartment of Chemical Engineering
Placidus B. Amama
The continued depletion of fossil fuels and concomitant increase in greenhouse gases have encouraged worldwide research on alternative processes to produce clean fuel. Fischer-Tropsch synthesis (FTS) is a heterogeneous catalytic reaction that converts syngas (CO and H₂) to liquid hydrocarbons. FTS is a well-established route for producing clean liquid fuels. However, the broad product distribution and limited catalytic activity are restricting the development of FTS. The strong interactions between the active metal catalyst (Fe or Co) and support (Al₂O₃, SiO₂ and TiO₂) during post-synthesis treatments of the catalyst (such as calcination at ~500°C and reduction ~550°C) lead to formation of inactive and unreducible inert material like Fe₂SiO₄, CoAl₂O₄, Co₂SiO₄. The activity of FTS catalyst is negatively impacted by the presence of these inactive compounds. In our study, we demonstrate the use of a modified photo-Fenton process for the preparation of carbon nanotube (CNT)-supported Co and Fe catalysts that are characterized by small and well-dispersed catalyst particles on CNTs that require no further treatments. The process is facile, highly scalable, and involves the use of green catalyst precursors and an oxidant. The reaction kinetic results show high CO conversion (85%), selectivity for liquid hydrocarbons and stability. Further, a gaseous product mixture from FTS (C1-C4) was utilized as an efficient feedstock for the growth of high-quality, well-aligned single-wall carbon nanotube (SWCNT) carpets of millimeter-scale heights on Fe and (sub) millimeter-scale heights on Co catalysts via chemical vapor deposition (CVD). Although SWCNT carpets were grown over a wide temperature range (between 650 and 850°C), growth conducted at optimal temperatures for Co (850°C) and Fe (750°C) yielded predominantly SWCNTs that are straight, clean, and with sidewalls that are largely free of amorphous carbon. Also, low-temperature CVD growth of CNT carpets from Fe and Fe–Cu catalysts using a gaseous product mixture from FTS as a superior carbon feedstock is demonstrated. The efficiency of the growth process is evidenced by the highly dense, vertically aligned CNT structures from both Fe and Fe–Cu catalysts even at temperatures as low as 400°C–a record low growth temperature for CNT carpets obtained via conventional thermal CVD. The use of FTS-GP facilitates low-temperature growth of CNT carpets on traditional (alumina film) and nontraditional substrates (aluminum foil) and has the potential of enhancing CNT quality, catalyst lifetime, and scalability. We demonstrate growth of SWCNT carpets with diameter distributions that are smaller than SWCNTs in conventional carpets using a CVD process that utilizes the product gaseous mixture from Fischer-Tropsch synthesis (FTS-GP). The high-resolution transmission electron microscopic (HR-TEM) and Raman spectroscopic results reveal that the use of a high melting point metal as a catalyst promoter in combination with either Co (1.5 nm ± 0.7) at 850ºC or Fe (1.9 nm ± 0.8) at 750ºC yields smaller-diameter SWCNT arrays with narrow diameter distributions. Scalable synthesis of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and onion like carbon (OLC) in a batch reactor using supercritical fluids as a reaction media is demonstrated. The process utilizes toluene, ethanol, or butanol as a carbon precursor in combination with ferrocene that serves as a catalyst precursor and a secondary carbon source. The use of supercritical fluids for growth does not only provide a route for selective growth of a variety of carbon nanomaterials, but also provides a unique one-step approach that is free of aggressive acid treatment for synthesis of CNT-supported metallic nanoparticle composites for catalysis and energy storage applications.
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Oschatz, M., Deelen T. W. van, J. L. Weber, W. S. Lamme, G. Wang, B. Goderis, O. Verkinderen, A. I. Dugulan, and Jong K. P. de. "Effects of calcination and activation conditions on ordered mesoporous carbon supported iron catalysts for production of lower olefins from synthesis gas." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-224310.
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Lower C2–C4 olefins are important commodity chemicals usually produced by steam cracking of naphtha or fluid catalytic cracking of vacuum gas oil. The Fischer–Tropsch synthesis of lower olefins (FTO) with iron-based catalysts uses synthesis gas as an alternative feedstock. Nanostructured carbon materials are widely applied as supports for the iron nanoparticles due to their weak interaction with the metal species, facilitating the formation of catalytically active iron carbide. Numerous synthetic approaches towards carbon-supported FTO catalysts with various structures and properties have been published in recent years but structure-performance relationships remain poorly understood. We apply ordered mesoporous carbon (CMK-3) as a support material with well-defined pore structure to investigate the relationships between calcination/activation conditions and catalytic properties. After loading of iron and sodium/sulfur as the promoters, the structures and properties of the FTO catalysts are varied by using different calcination (300–1000 °C) and activation (350 or 450 °C) temperatures followed by FTO testing at 1 bar, 350 °C, H2/CO = 1. Carbothermal reduction of iron oxides by the support material occurs at calcination temperatures of 800 or 1000 °C, leading to a higher ratio of catalytically active iron(carbide) species but the catalytic activity remains low due to particle growth and blocking of the catalytically active sites with dense graphite layers. For the samples calcined at 300 and 500 °C, the formation of non-blocked iron carbide can be enhanced by activation at higher temperatures, leading to higher catalytic activity. Olefin selectivities of ∼60%C in the formed hydrocarbons with methane of ∼10%C are achieved for all catalysts under FTO conditions at low CO conversion. The influence of the calcination temperature is further investigated under industrially relevant FTO conditions. Promoted CMK-3-supported catalysts obtained at low calcination temperatures of 300–500 °C show stable operation for 140 h of time on stream at 10 bar, 340 °C, H2/CO = 2.
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Morrill, Michael R. "Higher alcohol synthesis on magnesium/aluminum mixed oxide supported potassium carbonate promoted molybdenum sulfide." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52190.
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Higher alcohols synthesized via CO hydrogenation reactions have been a topic of intense study both in industry and academia for over thirty years. A variety of transition metals and promoters have been used in catalysts for this reaction. MoS₂, in particular, is popular due to its low cost, resistance to sulfur poisoning, and ability to selectively produce higher alcohols over hydrocarbons.
The bulk material has a rich history in hydrodesulfurization reactions (HDS), and as such, a great deal is known about the material's structure and reactivity. However, even with this deep body of knowledge about the bulk catalyst, no one has yet been able to implement an industrially viable variation of the catalyst to make higher alcohols.
Supported MoS₂ has also been studied for the same purpose. Generally, supports are employed to improve catalyst productivity per gram of Mo by dispersing the metal and increasing the amount of catalytically active surface area. However, product selectivity may also be influenced by chemical properties of the supports. Specifically, gamma alumina has been shown to raise hydrocarbon formation due to intrinsic surface acidity.
The effects of basic supports are reported on the CO hydrogenation reaction are reported. K promoted Mo is supported on two basic materials - commercial sepiolite (Si₁₂Mg₈O₃₀(OH)₄) and hydrotalcite-derived Mg/Al mixed metal oxides (MMO). The catalysts are reacted with syngas, and the resultant product selectivities are compared at isoconversions. Activated carbon supported Mo and bulk MoS₂ are also used as controls. It is shown that MMO provides a unique promotional effect by suppressing methanol formation and favoring higher alcohols.
The specific role of MMO in the reaction is investigated by combining it in three different ways with Mo. 1) MMO is impregnated with Mo in the classic fashion. 2) Bare MMO or MMO/K is placed as a secondary bed downstream of the principle catalyst (K promoted Mo supported on MMO). 3) Bare MMO or MMO/K is mixed with the principle catalyst to make a homogeneous bed.
It is shown that MMO by itself is somewhat inert in the reaction while MMO/K has some higher alcohol forming activity. More importantly however, it is shown that the MMO:Mo ratio has far greater effects on selectivity than the morphology of MoS₂. There is evidence however that MoS₂ morphology can affect activity. It is hypothesized that a greater degree of stacking in MoS₂ domains leads to reduced activity.
The existence of coupling and homologation pathways are investigated by feeding methanol or ethanol into the syngas as it enters the catalyst bed. By comparing changes in the productivity of different higher alcohols with the liquid feed, it is shown that an MMO supported catalyst is much more reactive with methanol and somewhat more reactive with ethanol than its bulk MoS₂ counterpart. It is shown that for both the bulk and supported catalysts, the addition of a Cx alcohol results in the largest increase in Cx+1 products, suggesting that alcohol homologation is in fact the most favored route to higher alcohols by these materials.