MSc., Faculty of Science, University of the Witwatersrand, 2011 / A study was performed in order to investigate the effect of preparation method and the effect of microwave heating on a manganese promoted iron based Fischer-Tropsch catalyst. The effects of preparation method and microwave heating on the structure and morphology of the catalyst, its surface area and reduction behavior were investigated using various techniques such as Transmission electron microscopy (TEM), Powder x-ray diffraction (PXRD), surface area measurements (BET) and temperature programmed reduction (TPR). The FTS performance of the catalysts were also studied using a fixed bed reactor with Fischer-Tropsch Synthesis conditions (270 C, flow rate of 30 ml/min, H2/CO ratio = 2, pressure of 10 bar). Characterization of the catalysts calcined at 350 C revealed that manganese enriched the surface of impregnated Mn/Fe catalysts and suppressed the reduction of the iron catalyst. However, the Mn acted as a structural promoter in the co-precipitated catalysts and also promoted the reduction of Fe2O3 as the manganese content increased. The co-precipitated catalyst calcined at 650 C suppressed the reduction of iron. The impregnated catalysts showed similar conversion (~ 70%) for catalysts with Mn loadings 5%, 10% and 20%. This suggests Mn promotes the activity of the iron catalyst since less iron is present in the catalyst as the manganese loading is increased. The co-precipitated catalysts showed a 10 wt% Mn loading to be the optimum amount for increased activity and selectivity to C2 – C4 hydrocarbons, lower molecular weight olefins and a lower selectivity to heavier molecular weight hydrocarbons relative to Mn loadings of 5, 20 and 50 wt%. Mn loadings in excess of 10 wt% showed a slight increase in selectivity to heavier weight hydrocarbons. The impregnated catalysts showed very little difference in activity and selectivity but the co-precipitated catalyst showed a decrease in activity after the catalyst was microwave heated. A slight increase in selectivity to lower weight olefins and heavier molecular weight hydrocarbons was noted after microwave heating. The TPSR (Temperature programmed surface reaction) results revealed that this may be due to the stronger adsorption of CO on the surface of the catalyst after microwave heating. A similar trend was observed for catalysts promoted with 0.1 wt% potassium i.e. a slight increase in selectivity to heavier weight hydrocarbons after microwave heating.

Faculty of Science School of Chemistry 9911467t EMMA.MOKOENA@sasol.com / The objective of the study was to prepare novel silica materials and then use them as supports/binders for the Fisher-Tropsch (F-T) reaction. Hence the thesis is divided into two parts - (i) the synthesis of silica materials (ii) use of silica materials as supports. PART I The studies that were carried out in this thesis evaluated the effect of templates and synthesis conditions on the nano- and microstructure and properties of silica materials that are obtained by the sol-gel method. The studies with DL-tartaric acid and citric acid as templates revealed that synthesis conditions (temperature, NH4OH concentration, water/ethanol concentration, time before NH4OH addition, static versus stirred conditions, stirring rate and solvent) all have an effect on the microstructure of the silica and influence the formation of particular silica morphologies. DL-tartaric acid produced longer and more uniform tubes when compared to citric acid. Tubes that are formed by DL-tartaric acid are hollow and open ended; however the ones formed in citric acid are a mixture of filled and hollow but closed tubes. Hollow spheres are exclusively formed when citric acid is used under certain conditions while only filled spheres are formed when DL-tartaric iii acid is used. The surface areas of the silicas formed from DL-tartaric acid are lower that the surface areas obtained for materials produced by citric acid. The nitrogen adsorption-desorption isotherms of silica materials obtained from both templates showed that the materials were mesoporous with some microporosity present in them. Studies with mucic and tartronic acids as templates also showed that the template as well as the synthesis conditions (such as solvent, temperature and stirring) affect the resulting silica morphology. Mucic acid produced silica materials with high surface areas, mesopores and a morphology that reveals fragmented tubes. Tartronic acid produced hollow tube materials with low surface areas and a combination of micro- and mesopores. The yield of the tubes was higher at lower temperatures for both templates. When sugars (e.g. glucose) were used only spherical particles were obtained and some sugars gave particle sizes that are smaller than the ones that are normally obtained by the sol-gel method. PART II Catalysts (Fe/Cu/K) supported on a range of silica materials with different morphologies (hollow nanotubes, hollow spheres, Stöber/closed spheres) were evaluated in the Fischer-Tropsch reaction (8 bar, 250 °C, 400 h-1 GHSV). The supported iron catalysts modified the physico-chemical properties and activity of iv the catalysts but not the catalyst selectivity. A Ruhrchemie catalyst (known F-T catalyst standard) was also evaluated under the same reaction conditions as the new catalysts for comparison purposes. The Ruhrchemie catalyst was found to be the most active catalyst followed by the catalyst supported on nanotubes, Stöber spheres and hollow spheres respectively. Catalysts containing 18% silica showed the best activity compared to the 9% and 27% silica catalysts. The product distribution and WGS activity were largely influenced by the potassium that is present in the samples and not the support type. Mössbauer spectroscopy showed that some active catalysts contained χ' – Fe2.5C and some superparamagnetic iron oxides or carbides while other catalysts also contained α – Fe and Fe3O4 in addition to χ' – Fe2.5C and some superparamagnetic iron oxides or carbides species. This finding supports the hypothesis that carbide formation is a requirement for active F-T catalysts. It also suggests that metallic iron is necessary for carbiding to occur, hence the need for a reduction pre-treatment.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 483-489. / by George Albert Huff, Jr. / Sc.D.

Transition metals have been extensively studied as catalysts, and certain metals are known to be highly selective and active for certain processes. It is possible to use metal clusters as models for reactions occurring at metal surfaces, but it is often found that in practical applications these complexes are unstable and break down. It is possible to support or stabilise a metal species on, or in, an inorganic framework, making heterogeneous catalysts. A study of metal cluster chemistry with mixed-donor phosphine ligands was conducted, with several new ruthenium complexes synthesised. The chemistry of metal-sulfur interactions is applicable to the removal of sulfur from crude oil, and in an investigation to this chemistry, the bifunctional ligand HSCH2CH2PPhH was added to ruthenium clusters (Chapter 2). The addition of this sulfur-phosphine ligand to the cluster [Ru3([mu]-dppm)(CO)10] produced the carbonyl substituted cluster [Ru3([mu]-dppm)(H)(CO)7(SCH2CH2PPhH)] and the bridged complex [Ru3([mu]-dppm)(H)(CO)8(SCH2CH2PPhH)Ru3([mu]-dppm)(CO)9], as well as recovery of the starting material. Further reactions with this ligand were examined with [Ru3(CO)12] and other complexes were synthesised with different clusters and ligands (Chapter 2). The M41S materials, MCM-41 and MCM-48, are well ordered porous materials with high surface areas (Chapter 3). The incorporation of three different types of metal species, metallosurfactants, metal clusters and nanoparticles, into these materials was examined in an attempt to make heterogeneous catalysts for the Fischer-Tropsch process. The success of this was studied using characterisation techniques such as powder X-ray diffraction, transmission electron microscopy and BET surface area measurements. Metallosurfactants containing either copper or cobalt were added directly to the synthesis of the porous materials in an attempt to incorporate the metals into the framework structure of the porous silica (Chapter 3). This resulted in well ordered iv porous materials, but the successful incorporation of the metal species was found to be dependent on several factors. Organometallic clusters containing metals such as copper, iron and ruthenium, with supporting carbonyl ligands, were added post-synthesis to MCM-41 and MCM-48 (Chapter 4). Various reaction conditions were examined in attempts to ensure small particle formation. The optimum incorporation of nanoparticles containing iron and platinum was found to occur when a suspension of pre-made and purified nanoparticles was added post-synthesis to the M41S materials (Chapter 4). These materials resulted in porous silicas with well dispersed, small metal particles. The optimum conditions for the calcination of these new materials were determined, in an attempt to remove the ligands and stabilisers and retain the small metal particle size (Chapter 5). Testing for the Fischer-Tropsch process was conducted in a fixed bed reactor through which a flow of synthesis gas containing carbon monoxide and hydrogen could pass over the material (Chapter 5). Analysis by gas chromatography showed that the major product produced by all materials tested was methane, but other hydrocarbons were produced in small amounts, including hexane.

During this PhD thesis, cobalt (Co) catalysts have been prepared, characterized and studied in the carbon monoxide hydrogenation (CO+H2) reaction (also known as “Fischer-Tropsch” (FT) reaction). In industry, the FT synthesis aims at producing long chain hydrocarbons such as gasoline or diesel fuels. The interest is that the reactants (CO and H2) are obtained from other carbonaceous sources than crude oil: natural gas, coal, biomass or even petroleum residues. As it is well known that the worldwide crude oil reserves will be depleted in a few decades, the FT reaction represents an attractive alternative for the production of various fuels. Moreover, this reaction can also be used to produce high value specialty chemicals (long chain alcohols, light olefins…). Two different types of catalysts have been investigated during this thesis: cobalt with magnesia used as support or dispersant (Co/MgO) and cobalt with silica used as support (Co/SiO2). Each catalyst from the first class is prepared by precipitation of a mixed Co/Mg oxalate in acetone. This coprecipitation is followed by a thermal decomposition under reductive atmosphere leading to a mixed Co/MgO catalyst. On the other hand, Co/SiO2 catalysts are prepared by impregnation of a commercial silica support with a chloroform solution containing Co nanoparticles. This impregnation is then followed by a thermal activation under reductive atmosphere. The mixed Co/Mg oxalates and the resulting Co/MgO catalysts have been extensively characterized in order to gain a better understanding of the composition, the structure and the morphology of these materials: thermal treatments under reductive and inert atmospheres (followed by MS, DRIFTS, TGA and DTA), BET surface area measurements, XRD and electron microscopy studies have been performed. Moreover, an original in situ technique for measuring the H2 chemisorption surface area of catalysts has been developed and used over our catalysts. The performances of the Co/MgO and Co/SiO2 catalysts have then been evaluated in the CO+H2 reaction at atmospheric pressure. Chemical Transient Kinetics (CTK) experiments have been carried out in order to obtain information about the reaction kinetics and mechanism and the nature of the catalyst active surface under reaction conditions. The influence of several experimental parameters (temperature, H2 and CO partial pressures, total volumetric flow rate) and the effect of passivation are also discussed with regard to the catalyst behavior. Our results indicate that the FT active surface of Co/MgO 10/1 (molar ratio) is entirely covered by carbon, oxygen and hydrogen atoms, most probably associated as surface complexes (possibly formate species). Thus, this active surface does not present the properties of a metallic Co surface (this has been proved by performing original experiments consisting in switching from the CO+H2 reaction to the propane hydrogenolysis reaction (C3H8+H2) which is sensitive to the metallic nature of the catalyst). CTK experiments have also shown that gaseous CO is the monomer responsible for chain lengthening in the FT reaction (and not any CHx surface intermediates as commonly believed). Moreover, CO chemisorption has been found to be irreversible under reaction conditions. The CTK results obtained over Co/SiO2 are quite different and do not permit to draw sharp conclusions concerning the FT reaction mechanism. More detailed studies would have to be carried out over these samples. Finally, Co/MgO catalysts have also been studied on a combined DRIFTS/MS experimental set-up in Belfast. CTK and Steady-State Isotopic Transient Kinetic Analysis (SSITKA) experiments have been carried out. While formate and methylene (CH2) groups have been detected by DRIFTS during the FT reaction, the results indicate that these species play no role as active intermediates. These formates are most probably located on MgO or at the Co/MgO interface, while methylene groups stand for skeleton CH2 in either hydrocarbon or carboxylate. Unfortunately, formate/methylene species have not been detected by DRIFTS over pure Co catalyst without MgO, because of the full signal absorption.

This thesis describes results of a study aimed at developing and evaluating attrition resistant iron catalysts prepared by spray drying technique. These catalysts are intended for Fischer-Tropsch (F-T) synthesis in a slurry bubble column reactor (SBCR). One of the major challenges associated with the use of SBCR for this purpose is the problem of catalyst/wax separation. If the catalyst particles break up into smaller ones during the F-T synthesis, these small particles (>5-10 m in diameter) will cause problems with the catalyst/wax separation. Several research groups have worked on development of attrition resistant spray-dried iron catalysts, and methodology to measure and predict their attrition behavior. However, these attrition tests were not conducted under conditions representative of those encountered in a SBCR. In this work, the attrition behavior of six spray-dried catalysts and two precipitated catalysts was evaluated under slurry reaction conditions in a stirred tank slurry reactor (STSR). Spray-dried catalysts used in this study were prepared at Texas A&M University (TAMU) and at Hampton University (HU), employing different preparation procedures and silica sources (potassium silicate, tetraethyl orthosilicate or colloidal silica). The attrition properties of F-T catalysts were determined by measuring particle size distribution (PSD) of catalysts before and after F-T synthesis in the STSR. This provides a direct measure of changes in particle size distribution in the STSR, and accounts for both physical and chemical attrition effects. Also, scanning electron microscopy (SEM) was used to investigate the mechanism of attrition - erosion vs. fracture, and to obtain morphological characteristics of catalysts. Spray dried 100Fe/3Cu/5K/16SiO2 catalyst (WCS3516-1), prepared from wet precursors using colloidal silica as the silica source, was the best in terms of its attrition strength. After 337 hours of F-T synthesis in the STSR, the reduction in the average particle size and generation of particles less than 10 m in diameter were found to be very small. This indicates that both particle fracture and erosion were insignificant during testing in the STSR. All other catalysts, except one of the spray dried catalysts synthesized at Hampton University, also had a good attrition resistance and would be suitable for use in slurry reactors for F-T synthesis.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xvi, 148 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 162-183).

This dissertation explores catalyst technology for the production of renewable liquid fuels via thermo-chemical conversion of biomass derived syngas. Fischer-Tropsch synthesis is a process for converting syngas, i.e. a mixture of CO and H2, into energy rich long chain hydrocarbons and oxygenated compounds. This synthesis process involves a number of elementary reactions leading to an array of polymeric products. The economic operation of an FTS process lie in the interplay of both catalyst and reactor design. In relation to catalysis, the nature of chemisorbed species, and the fractional availability of active metal sites determines rate, conversion and yield. Similarly, reactor design decides the operational envelope and determines the economics of an FTS process. Eggshell cobalt catalysts are used in CO hydrogenation reactions due to their ability to maximize the use of precious cobalt metal. The thickness of the shell can be utilized to control the product yield and distribution. In this study, during catalyst synthesis stage, metal-support interaction has been exploited to control the thickness and hence, the product distribution. The catalysts are prepared using precipitation of cobalt nitrate (dissolved in ethanol) on silica support. The metal deposition rate and the location are controlled through optimized non-polar solvent imbibing, followed by water addition to a Co(NO3)2-ethanol solution and hydrolysis by urea. The eggshell coating thickness (in the absence of restricting solvent) onto silica gel substrate was modeled via theoretical equations and experimentally verified during catalyst preparation through microscopic analysis of catalyst samples. Bulk precursor solution properties such as viscosity and surface tension along with substrate properties such as tortuosity are analyzed and included in the theoretical analysis for tailoring the catalyst eggshell thickness. Polar and non-polar solvent interactions with silica gel are exploited during cobalt precipitation to control the eggshell thickness. The catalyst samples were characterized using hydrogen chemisorption studies. The catalyst was tested in a fixed bed tubular bench scale reactor using research grade synthetic feed gases (H2:CO being 2:1). Products were analyzed in a GC column fitted with flame ionized detector and the results were compared with Anderson-Schulz-Flory distribution. Liquid product analysis validated the approach used for eggshell catalyst design and synthesis. The impact of solvent and calcination conditions, on the performance of eggshell catalysts was examined. Solvents such as water and alcohol attach to the silanol groups on the silica gel surface and compete with metal salts during ion exchange and adsorption. The solution properties impact metal dispersion and interaction with metal support. The calcination conditions (static versus dynamic, oxidizing versus reducing atmosphere) also have an impact on metal dispersion and support interaction. Ethanol proved to be a better solvent for enhancing the dispersion due to its surface wetting properties. Direct reduction in dynamic hydrogen provided gradual decomposition of the cobalt precursor thus reducing agglomeration. Both the use of water as a solvent and a static air environment during calcination led to lower dispersion. The back reaction of calcination products (especially H2O) and agglomeration due to thermal expansion were competing phenomenon in a static oxidizing environment. Catalyst characterization revealed that the latter effect was pre-dominant. Catalyst performance testing was first done with pure gases (H2 & CO) in a fixed bed reactor. Additionally, to examine the technological feasibility and economic viability of producing liquid fuels from biomass via the thermo-chemical route, laboratory scale testing was done using syngas produced by gasification of pine chips. The pine chips were gasified in a tubular entrained flow gasifier operated at MSU and supplied in cylinders. The raw biomass syngas was treated using a series of adsorbents to remove tar, water and other impurities. This pre-treated gas was subjected to Fischer-Tropsch Synthesis (FTS) in a bench scale fixed bed reactor using the eggshell cobalt catalyst developed in our laboratory. Hydrogen was added to attain the 2:1 stoichiometric ratio required for the FTS reaction. The product gases were analyzed using an FTIR gas cell while liquid product was analyzed using a GC/MS HP-5 column. The eggshell catalyst produced fuel preferentially in the range of middle distillates. The activity of FTS catalyst under biomass derived syngas was lower when compared to that under pure surrogates (H2/CO) due to the presence of inert components (such as methane) in the biomass derived syngas To complement the experimental study, a comprehensive model of FTS catalytic process was developed. This included both catalyst and a fixed bed reactor model. While modeling a catalyst pellet, intra-particle diffusion limitation was taken into account. For a spherical 2mm pellet, eggshell morphology provided highest activity and selectivity. The reactor model was developed by coupling intra-pellet model with inter-pellet model via reaction term. The entire process operation starting with gas injection was considered. Presence of radial temperature profile, due to wall cooling, was confirmed by Mears criterion. Thus for a fixed time duration, a 2-dimensional reactor model, with respect to temperature and concentration, was developed. The safe operational envelopes for a fixed bed reactor, using cobalt catalyst, was narrow 473 < T < 493. The extent of catalyst pore fill changed (i) the radial thermal conductivity (ii) the overall temperature and concentration profile across the bed and (iii) the limits of safe operation without reaction runaway. Finally, hydrocarbon product selectivity also varied during startup. While the catalyst pores were being filled, effluent product mainly composed of lighter, more volatile components. Once the pores are filled, heavier products started to trickle down the bed. The economics of a large scale production of liquid fuels using this technology was explored using a CHEMCAD model of a large scale process for producing liquid fuel from biomass, a sensitivity study was conducted to determine key process parameters Two different gasification technologies were compared, one that uses only biomass (BTL process) and a second process that supplements the biomass feed with natural gas for meeting energy and hydrogen needs (BGTL process). The basis for the design was 2000 metric tons of dry biomass feed per hour. The breakeven price for synthetic crude oil was estimated at $106/bbl. for the BTL plant, and $88/bbl. for a natural gas assisted BGTL plant using current market prices for raw materials utilities and capital equipment. With the increasing availability, and falling prices of natural gas, the reforming of natural gas will provide a bridge solution in the short term for economical natural gas assisted BTL conversion, thus making it competitive in marketplace.

Fischer-Tropsch Reaction Water (FTRW) is a high organic strength wastewater produced as a by-product in Sasol’s Fischer-Tropsch Reactors. Typically it has an organic load of 18000 mgCOD/L and is highly acidic with a pH of approximately 3.8. It is deficient in nutrients (N and P and other micronutrients). This dissertation deals with the biological and physico-chemical model development of a dynamic anaerobic digestion model, and explores two different approaches to representing the physico-chemical processes that complement and interact with the bioprocesses. The performances of the resultant two dynamic models (ADFTRW1 & AD-FTRW2) were compared in order to assess to what extent the more detailed and rigorous ionic speciation modeling in AD-FTRW2 addressed the shortcomings attributed to the simplified physicochemical modeling in AD-FTRW1. The ionic speciation model used in AD-FTRW2 uses a classic equilibrium formulation along the same lines as in the UCTADM2 model for anaerobic digestion of municipal wastewater sludges (Brouckaert et al., 2010), while AD-FTRW1 uses a simplification of the approach developed by Musvoto et al. (2000) in order to represent short chain fatty acid (SCFA) dissociation and the weak acid base chemistry of the inorganic carbon system. A 44 day extract from a 700 day laboratory-scale dataset (Van Zyl et al. 2008) was used as the basis for comparing the models. During this period the membrane bio-reactor was subjected to varying flow and load conditions. To validate the models, the experimentally measured and model predicted process variables of reactor alkalinity, reactor pH, biogas production and effluent SCFA concentration were compared. It was found that AD-FTRW2 provided superior agreement with pH data, but predictions of alkalinity, gas production rate and effluent short-chain fatty acids were not significantly improved in AD-FTRW2 relative to AD-FTRW1. This outcome was hypothesized since pH is strongly dependent on physico-chemical processes such as ionic interactions in solution and gas exchange which were the components to the models (AD-FTRW1 versus AD-FTRW2) which differed most significantly. Alkalinity, which is also highly influenced by physico-chemical model representations showed substantial improvement however statistical analysis could not show this improvement to be significant. The other two variables that were compared, biogas production and effluent SCFA concentration, displayed very similar agreement with experimental data. These variables depend more on mass balance effects and biological kinetics and were therefore not significantly altered by the more rigorous handling of aqueous chemistry in AD-FTRW2. It was concluded that AD-FTRW2 constitutes an improvement in model predictive power over AD-FTRW1 at a small cost in computing time. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

La recherche sur la synthèse Fischer-Tropsch (FTS) a depuis 20 ans été fortement stimulée par la demande d’énergie croissante. Le projet de ce doctorat vise à élaborer un catalyseur nanométrique hétérogène sans porosité interne qui sera utilisé avec du gaz de synthèse produit par gazéification sous air de matières renouvelables. Les objectifs principaux consistent à valider un protocole de fabrication du catalyseur par plasma, optimiser les conditions d’opération, comparer avec une option commerciale, évaluer le potentiel des additifs et concevoir un modèle cinétique. Le catalyseur est constitué de nanoparticules de carbure de fer encapsulées dans du carbone devant être au moins partiellement enlevé avant la réaction. Un réacteur a été conçu et les conditions optimales ont été estimées à : • température inférieure à 250°C pour limiter la réaction de conversion du gaz à l’eau (water-gas-shift; WGS) tout en maintenant une activité optimale pour la FTS; • pression supérieure à 15 bars pour assurer que le milieu liquide de la réaction soit saturé en réactifs, mais inférieure à 25 bars pour permettre l’évacuation de l’eau; • une vitesse spatiale de 1 200 ml[indice inférieur gaz]/(h*g[indice inférieur cata]) qui assure une conversion maximale aux autres conditions optimisées. Du Nanocat, un matériel commercial constitué de nanoparticules d’hématite non-supportées, a été utilisé comme matériel de référence. Il doit toutefois être transformé en carbure de fer par une réaction avec du CO. Dans le système de réaction et les conditions testées, les performances du Nanocat sont très similaires à celle du catalyseur produit par plasma. Du Cu et du K ont été utilisés comme dopants du catalyseur; le dopage est simultané à la fabrication du catalyseur. Une conversion complète et sans désactivation a été obtenue, mais l’étendue de la réaction WGS a été multipliée par 3. Ce dopage s’est avéré bénéfique mais une optimisation de la charge est requise. Le modèle choisi pour simuler la FTS est basé sur une cinétique phénoménologique : les paramètres de la réaction sont réunis en un facteur mis en fonction d’une réponse du système réactionnel. La prédiction du modèle phénoménologique est bonne pour la conversion du CO et pour la WGS, mais pas pour la conversion FTS; il donne aussi de bons résultats avec des données de la littérature.