Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2017. / One of the very promising synthetic fuel production strategies is the Fischer-Tropsch process, founded on the Fischer-Tropsch Synthesis, which owes its discovery to the namesake researchers Franz Fischer and Hans Tropsch. The Fischer-Tropsch Synthesis (FTS) converts via complex polymerisation reaction a mixture of CO and H2 over transition metal catalysts to a complex mixture of hydrocarbons and oxygen containing compounds with water as major by-product. The mixture of CO and H2 (termed syngas) may be obtained by partial oxidation of carbon containing base feedstocks such as coal, biomass or natural gas via gasification or reforming. The Fischer-Tropsch (FT) process thus presents the opportunity to convert carbon containing feedstocks to liquid fuels, chemicals or hydrocarbon waxes, which makes, for instance, the monetisation of stranded gas or associated gas a possibility. The FT-process is typically carried out in two modes of operation: low temperature Fischer-Tropsch (LTFT) and high temperature Fischer-Tropsch (HTFT). LTFT is normally operated at temperatures of 200 – 250 °C and pressures of 10 – 45 bar to target production of high molecular weight hydrocarbons, while HTFT is operated at 300 – 350 °C and 25 bar to target gasoline production. The catalytically active metals currently used commercially are iron and cobalt, since product selectivity over nickel is almost exclusively to methane and ruthenium is highly expensive in addition to requiring very high pressures to perform optimally. Fe is much cheaper, but tends to deactivate more rapidly than Co due to oxidation in the presence of high H2O partial pressures. One of the major drawbacks to using Fe as FT catalyst is the requirement of lower per pass conversion which necessitates tail gas recycle to extend catalyst life and attain acceptable overall conversions. A more active or similarly active but more stable Fe-catalyst would thus be advantageous. For this reason promotion of a self-prepared typical LTFT Fe-catalyst with Ru was investigated. A precipitated K-promoted Fe-catalyst was prepared by combination of co-precipitation and incipient wetness impregnation and a ruthenium containing catalyst prepared from this by impregnation with Ru3(CO)12. The catalysts, which had a target composition of 100 Fe/30 Al2O3/5 K and 100 Fe/30 Al2O3/5 K/3 Ru, were characterised using XRD, SEMEDX, ICP-OES, TPR and BET N2-physisorption, before testing at LTFT conditions of 250 °C and 20 bar in a continuously stirred slurry phase reactor.

Iron Fischer-Tropsch (FT) catalysts are typically prepared as iron oxides which are reduced to FT-active iron metal and iron carbide prior to FT synthesis. The iron oxides contain a variety of different chemical and structural promoters to alter FT-activity. Silica is a common structural promoter which stabilises the formation of small crystallites and provides mechanical integrity to the catalyst. However, silica inhibits the reduction of the oxide precursor to the FT-active phases. This ultimately affects catalyst activity and product selectivity. It has been proposed that the silica interacts with the iron to form encapsulating shells of fayalite (Fe2SiO4), or fayalite rafts between the iron oxide and the silica support. In this study, six silica-promoted iron oxide samples were prepared using a simple co-precipitation technique. Samples contain varying amounts of silica, and the samples are named 100/x Fe/SiO2, where x is the weight of silica for 100 weight iron, with x taking on values of 0, 10, 25, 50, 100 and 200. The resulting iron oxides were characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRPD), M¨ossbauer spectroscopy (MS), magnetic susceptibility measurements (MM), Raman spectroscopy, thermal gravimetric analysis (TGA) and nitrogen physisorption. Their reduction in a hydrogen atmosphere was investigated using temperature programmed reduction (TPR), in situ XRPD and TEM. The reduction in hydrogen of 100/0 Fe/SiO2 and 100/10 Fe/SiO2 was also studied using in situ gas flow TEM cells. These cells allow the samples to be studied in the electron microscope at temperature and pressure conditions approaching those experienced in a real reactor environment. In the absence of a silica promoter (100/0 Fe/SiO2), hematite particles are formed with mean particle diameters of 39 ± 12 and 52.7 ± 0.2 nm determined using TEM and XRPD respectively. MM data reveals a magnetic transition (Morin transition) at≈230 K, consistent with a mean particle size of≈50 nm. In a hydrogen atmosphere, the hematite reduces to metallic iron via a two-step process viz. hematite → magnetite → iron. The final iron particles have an average crystallite size of 68.0 ± 0.2 nm. The presence of lower amounts of silica in the samples 100/10 Fe/SiO2, 100/25 Fe/SiO2 and 100/50 Fe/SiO2 results in the formation of silicasubstituted 2-line ferrihydrite particles. Bands in the Raman spectra of these samples shift on increasing silica content, which indicates an increasing number of Fe-O-Si bonds within the ferrihydrite framework. MM reveals typical superparamagnetic (SPM) behaviour above a blocking temperature in the range 39 - 68 K which gives mean particle sizes of 4.2, 3.6 and 3.5 nm for 100/10 Fe/SiO2, 100/25 Fe/SiO2 and 100/50 Fe/SiO2 respectively, in good agreement with particle sizes determined using TEM (3.1±0.4, 2.4±0.3 and 2.4±0.3 nm respectively). MS data at 300 K and 4.2 K were fitted with distributions of ∆EQ and Bhf respectively. The median values of Bhf decrease with increasing silica content, indicating greater degrees of distortion in the Fe3+ environments induced by increased silica substitution. The reduction to metallic iron occurs via a three-step process viz. hematite → magnetite → wu¨stite → iron, with the silica stabilising the wu¨stite phase. The increasing amount of Fe-O-Si bonds on increasing silica content shifts reduction to higher temperatures broadens each reduction step as a result of local Fe-O-Si concentration variations. Fractions of each sample are not completely reduced even at 1000°C, with the relative proportion increasing with increasing silica content. In situ gas flow TEM studies reveal that the mechanism of reduction involves the liberation of atomic iron atoms from the silica-substituted iron oxides which agglomerate and grow into final iron particles. This leaves a poorly crystalline Fe-O-Si bonded framework behind. STEM-EDS and STEM-EELS reveal low concentrations of silicon at the surface of the resulting iron particles, however they do not form encapsulating shells of fayalite as previously suggested. The majority of the silica remains in the Fe-O-Si material which may crystallise into separate fayalite particles at elevated temperature. The presence of silica in high proportions (100/100 Fe/SiO2 and 100/200 Fe/SiO2) results in the formation of a two-phase system consisting of silicasubstituted 2-line ferrihydrite particles which are encapsulated in an ironinfused amorphous silica network. As with the other silica-bearing samples, there is an increase in Fe-O-Si bonds and an increase in the degree of distortion at Fe3+ sites with increasing silica content. The large amount of silica suppresses the blocking temperature of the SPM crystallites. In a hydrogen atmosphere, the reduction to metallic iron follows the same three step process as the other silica-bearing samples. Reduction temperatures are further shifted to higher values and given reduction steps are considerably broader with increasing silica content. The fraction of iron not fully reduced also increases. Iron particle diameters are very small, since encapsulation by the silica matrix prevents growth of particles.

Iron carbides are amongst the crystalline phases formed during Fischer-Tropsch synthesis to produce hydrocarbons (Dry, 1990, Niemantsverdriet et al., 1980), using iron catalysts. The small crystallite size of the iron carbides causes peak broadening in XRD and prevented complete structure determinations in the past (Hagg, 1931; Retief, 1999; Senateur et al., 1962). Fortunately new instrumentation and techniques, such as fast powder X-ray diffractometers and software for structure determination, are now available to study crystal structures. Five different iron carbide phases are known to form during Fischer-Tropsch synthesis i.e. Hägg carbide (χ-Fe5C2), pseudo-hexagonal iron carbide (έ- Fe2.2C), hexagonal iron carbide (ε-Fe3C), Eckström-Adcock iron carbide (Fe7C3) and cementite (θ-Fe3C). Since the structure of cementite θ-Fe3C is well-known (Westgren & Phragmen, 1922) this study focused on the remainder, i.e. the determination of the crystal structures of the first four iron carbides: Hägg carbide (χ-Fe5C2), pseudo-hexagonal iron carbide (έ -Fe2.2C), hexagonal iron carbide (ε-Fe3C) and Eckström-Adcock iron carbide (Fe7C3). This study consisted of the preparation of iron carbides, structure determinations of these iron carbides, determination of reactions of the iron carbides during Fischer-Tropsch synthesis (FTS) (in situ XRD) and the stability of Hägg carbide (χ-Fe5C2) during FTS under commercial fixed bed reactor conditions. Time-temperature-transformation graphs were determined for iron catalysts with and without potassium promoter. The first step in the structure determination process was the preparation of almost pure samples. Samples of Hagg carbide (:t-FesC2), pseudo-hexagonal 8 -Fe22C iron carbide and hexagonal 1::-Fe3C iron carbide were prepared as pure as possible using the Anton Paar XRK600 reaction chamber attached to an X'Pert Pro multi-purpose diffractometer (N!PD). Eckstrom-Adcock iron carbide (Fe7C3) was available in spent catalyst from a fluidized-bed hydrocarbon synthesis plant at SASOL. These samples were characterized using room temperature and low temperature (77 K) Moss bauer absorption spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM, Philips CM200). Thermo-gravimetric analysis and conductivity measurements were done to characterize the carbonaceous species in the samples. Molecular modelling calculations were done using CASTEP (N!ilman et al., 2000; Payne et al., 1992) to determine the total lattice energies of the iron carbide structures.... / Prof. G.J. Kruger Prof. J.P.R. de Villiers

The global community has accepted Fischer Tropsch synthesis as one of the sustainable pathways to transportation fuels and chemicals due to the ever-depleting reserves of fossil fuels and its detrimental impact on the environment. However, the high capital investment and operating expenses associated with this technology have hampered its ability to compete with conventional petrochemicals. Some of the operating costs emanate from the choice of catalyst precursors and operational problems, which could lead to plant shutdowns. In recent times, few efforts have been made to explore cheaper FT catalysts to reduce operational costs, but the mechanical strength of solid FT catalysts, especially for pilot-scale fixed bed operations is not well represented in open literature. As a result, there is a high prevalence of mechanical failure of solid FT catalysts in pilot fixed-bed applications. In this study, we propose a scalable, Fischer Tropsch iron ore catalyst that is mechanically suited for fixed bed reactors to help address this issue. The catalyst development of the proposed iron ore catalyst involved the slurry phase impregnation of the precursor with copper and potassium and then shaping into spherical pellets with mass additions of 10%, 15% and 20% of bentonite(binder) on a rotating drum. There afterwards, the mechanical strength of each pelletized catalyst was tested using the single pellet crushing testing method (ASTM D 4179). These results were compared to the crushing strength of commercial spherical alumina to ascertain their suitability for fixed bed reactors. The most robust solid catalyst was the 10% binder iron ore pellets which recorded a single pellet crushing strength of 1833 kPa and was more than three times that of commercial spherical alumina and thus deemed apt for fixed bed reactors. A unique statistical approach was used to study the mechanical strength of the various binder combinations due to scattering in single pellet crushing strength data. The analysis revealed that the 10% binder iron ore pellets were most suited for laboratory FT runs and thus was tested for its catalytic performance. The FT runs revealed that the 10% binder iron ore catalyst had a CO conversion of 72.1 % and comparable to other similar iron-based FT catalysts reported in the literature. The proposed catalyst also showed a CH5+ selectivity of 83.2%, which was comparable the ones reported by other researchers. These findings provide a simple and cost- effect approach to upscale laboratory-scale FT catalyst designs to pre-emp its performance in pilot or industrial scenarios. / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

Thesis (PhD)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: This dissertation describes work done on Fischer- Tropsch ionomeric waxes. The waxes are characterized with respect to the method of manufacture, the mechanism of the oxidation process, the saponification, the physical properties, the rheological properties, the morphology and the water absorption of the waxes. Different methods of physical and mechanical analysis are used to prove at which concentration level, for each type of cation tested arid for each type of oxidized and grafted wax prepared, the formation of multiplets and clusters within the Fischer- Tropsch ionomeric waxes takes place. An understanding of multiplet and cluster formation in Fischer- Tropsch ionomeric waxes is essential as these morphological phenomena control the mechanical and physical behaviour of the Fischer- Tropsch ionomeric waxes. The ability to be able to analyse the Fischer- Tropsch ionomeric waxes for multiplet and cluster formation should allow one to predict the physical and mechanical behaviour of the Fischer- Tropsch ionomeric waxes in practical applications. / AFRIKAANSE OPSOMMING: Hierdie skripsie beskryf werk gedoen op Fischer-Tropsch ionomeries wasse. Die wasse is gekarakteriseer ten opsigte van die vervaardigingsmetode, die meganisme van oksidasie, die verseping, hulle fisiese en reologiese eienskappe, hulle morfologie en water absorpsie. Verskillende metodes van fisiese en meganiese analiese is gebruik om te bewys by watter konsentrasie, vir 'n spesifieke katioon en vir 'n spesifieke geoksideerde of entwas, wanneer veelvoud of tros-vorming plaasvind. Die vermoë om te verstaan hoe en wanner veelvoude en trosse in Fischer- Tropsch ionomeries wasse vorm is van kardinale belang, aangesien die fisiese en meganiese eienskappe van die Fischer- Tropsch ionomeries wasse direk beinvloed word deur die vorming van veelvoude en trosse. Die vermoë om Fischer- Tropsch ionemeries wasse te kan analiseer vir veelvoud en tros vorming is voordelig om Fischer- Tropsch ionomeries wasse se meganiese en fisiese eienskappe in praktiese aanwendings te voorspel.

The aim of this research project was to investigate the oxidation reactions of olefins to ketones. Initial studies revolved around the oxidation reactions of terminal olefins to symmetrical dialkyl ketones. The inability to isolate pure products, and the consumption of large amounts of the expensive palladium catalyst for each run as well as the extremely low yields that resulted from these oxidation reactions, made it difficult to thoroughly investigate this oxidation system. It was then decided to embark on the investigation of oxidation reactions of a-olefins to methyl ketones. For these studies, six terminal olefins were oxidised to methyl ketones employing seven different oxidation reactions. One of the most important and pioneering reactions m this field is the system employing PdCl2 / CuCl2 / O2 for the oxidation of terminal olefins to methyl ketones, namely the Wacker oxidation reaction. Experimental results, however, indicated that high product contamination from by-products resulted from these oxidation reactions despite the fairly good yields of product from the Wacker oxidation system. Some reaction systems that have been developed from the Wacker oxidation system were also investigated. The oxidation system employing PdCl2 / p-benzoquinone for the oxidation of terminal olefins to ketones was studied. The oxidation reactions resulted in incomplete oxidation with higher olefins (l-decene, l-nonene and l-octene), and complete oxidation of lower olefins (l-heptene, l-hexene and l-pentene) under the same reaction conditions. The products from lower olefins oxidised under these reaction conditions were pure and high yielding Another system that proved efficient both with feasibility and good yields of products was the oxidation system employing Pd(OAc)2 / H202 catalyst to oxidise terminal olefins to methyl ketones. Phase transfer catalysis has been employed in organic chemistry to effect different reactions. In this case two types of phase transfer agents were employed to effect the oxidation of terminal olefins to ketones. The first oxidation system involved the use of a PdCl2 / CuCl2 / O2 catalyst with a quaternary ammonium salt, cetyltrimethylammonium bromide (CTAB), to govern the course of the reaction. Reasonable yields were obtained, and moderate purity of products was also observed. The second phase transfer catalysis system employed polyethylene glycol (PEG-200) as a phase transfer agent, and PdCl2 / CuCl2 / O2 as a catalyst for oxidation of olefins to ketones. This oxidation system resulted in different isomers of a ketone from a terminal olefin. Pure methyl ketones were not isolable from the mixture of methyl and ethyl ketones. The oxidation reactions of olefins to ketones employing Pd(OAc)2 / p-benzoquinone in combination with electrolysis were also investigated. The unique feature about these reactions was the fact that cyclic olefins could also be oxidised under these conditions. Good yields were obtained, and high product purity was observed. One of the important oxidation reactions investigated during the project was the reaction that used an alternative metal to the expensive palladium catalyst for the oxidation reactions to ketones. This oxidation system employs CuCl2 / 18-C-6 / acetaldehyde as a catalyst for the oxidation of hydrocarbons to ketones and alcohols. It was discovered during the investigation that olefins can also be used as substrates and are oxidised to the corresponding ketones. The use of olefins as substrates resulted in higher yields than the hydrocarbon oxidation reactions, and less contamination in the product mixture was also observed. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Phllosophy. / A disadvantage of the Fischer-Tropsch synthesis is that a broad product spectrum is obtained. Economic considerations however require an improvement in the optimization of the reaction to maximize the production of high value commercial products, in·particular, short chain olefins and high molecular weight hydrocarbons. [Abbreviated abstract. Open document to view full version] / AC2017

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.

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.