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.

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.

This research project is part of a larger Canadian endeavour to evaluate feasibility of using new nanocatalyst formulations for Fischer-Tropsch synthesis (FTS) to convert fossil-derived or renewable gaseous fuels into green diesel. The green diesel is a clean fuel (with no aromatics and sulfur compounds) suitable for the commonly used transportation system. The catalyst investigated is cobalt metal supported on carbon nanotubes (CNTs). The physical properties of CNTs have improved the common cobalt catalyst currently used in industry. Carbon nanotubes have high surface area, a very stable for FTS activity and, contrary to other common supports, do not interact with the catalyst active phase to produce undesirable compounds. Moreover, CNTs differ from graphite in their purity and by their cylindrical form, which increases the metal dispersion and allows confinement of the particles inside the tubes. Thus, carbon nanotubes as a new type of carbon material have shown interesting properties, favoring catalytic activity for FTS cobalt catalyst. Their surface area can be modified from 170 to 214 m^2/g through acid treatment. The CNT support lowers the amount of Ru promoter needed to increase the catalyst activity up to 80 % CO conversion and potassium promoter increases the selectivity for á-olefins. The olefin to paraffin (O/P) ratio for Co/CNT and CoK/CNT are 0.76 and 0.90, respectively. Moreover, the Co-Fe bimetallic catalysts supported on CNT have proved to be much more attractive in terms of alcohol formation, up to 26.3 % for the Co10Fe4/CNT. The structural characteristics of CNTs have shown to be suitable for use as catalytic support materials for FTS using microemulsion preparation method as applied to produce nanoparticle catalysts. Microemulsion technique results show uniform nanoparticle that are easy to reduce. In addition, the confinement of the particles inside the CNT has improved the lifetime of the catalyst by decreasing the rate of sintering. The deactivation rate at high FTS activity is linear (XCO = -0.13 t(hr) + 75) and at low FTS activity is related to a power law expression of order 11.4 for the cobalt particles outside the tubes and 30.2 for the cobalt particles inside the tube. The optimized catalyst studied was the CoRuK/CNT catalyst. The best kinetic model to describe the CoRuK/CNT catalyst is: 18.5 x 10 ^-5 PH2^0.39/ (1 + 7.2 10 ^-2 PCO^0.72 PH2^0.1)^2.

This research project is part of a larger Canadian endeavour to evaluate feasibility of using new nanocatalyst formulations for Fischer-Tropsch synthesis (FTS) to convert fossil-derived or renewable gaseous fuels into green diesel. The green diesel is a clean fuel (with no aromatics and sulfur compounds) suitable for the commonly used transportation system. The catalyst investigated is cobalt metal supported on carbon nanotubes (CNTs). The physical properties of CNTs have improved the common cobalt catalyst currently used in industry. Carbon nanotubes have high surface area, a very stable for FTS activity and, contrary to other common supports, do not interact with the catalyst active phase to produce undesirable compounds. Moreover, CNTs differ from graphite in their purity and by their cylindrical form, which increases the metal dispersion and allows confinement of the particles inside the tubes. Thus, carbon nanotubes as a new type of carbon material have shown interesting properties, favoring catalytic activity for FTS cobalt catalyst. Their surface area can be modified from 170 to 214 m^2/g through acid treatment. The CNT support lowers the amount of Ru promoter needed to increase the catalyst activity up to 80 % CO conversion and potassium promoter increases the selectivity for á-olefins. The olefin to paraffin (O/P) ratio for Co/CNT and CoK/CNT are 0.76 and 0.90, respectively. Moreover, the Co-Fe bimetallic catalysts supported on CNT have proved to be much more attractive in terms of alcohol formation, up to 26.3 % for the Co10Fe4/CNT. The structural characteristics of CNTs have shown to be suitable for use as catalytic support materials for FTS using microemulsion preparation method as applied to produce nanoparticle catalysts. Microemulsion technique results show uniform nanoparticle that are easy to reduce. In addition, the confinement of the particles inside the CNT has improved the lifetime of the catalyst by decreasing the rate of sintering. The deactivation rate at high FTS activity is linear (XCO = -0.13 t(hr) + 75) and at low FTS activity is related to a power law expression of order 11.4 for the cobalt particles outside the tubes and 30.2 for the cobalt particles inside the tube. The optimized catalyst studied was the CoRuK/CNT catalyst. The best kinetic model to describe the CoRuK/CNT catalyst is: 18.5 x 10 ^-5 PH2^0.39/ (1 + 7.2 10 ^-2 PCO^0.72 PH2^0.1)^2.

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.

Several self-supported and metal oxide supported cobalt Fisher-Tropsch (FT) catalysts were prepared applying incipient wetness impregnation method. The catalysts were characterized by TPR, adsorption-desorption, XRD, TEM and SEM. The gas products were characterized by GC. The effect of support was investigated. The selfsupported 3D ordered macro-porous (3DOM) Fe-Co and self-supported 2D ordered mesoporous catalyst showed low or no activity under typical F-T reaction conditions. The 3DOM Al2O3 supported cobalt catalyst showed much higher CO conversion and C4+ selectivity than conventional Co/Gamma-Al2O3 catalyst. However, the 3DOM Co/Al2O3 prepared by incorporated method showed no activity. The supported Co/SBA-15 performed better CO conversion than the conventional Co/SiO2. The effects of temperature and time on 3DOM Co/Al2O3 and Co/SBA-15 system were coherent with traditional catalysts. The well-defined structure of 3DOM Al2O3 and SBA-15 may favor to the selectivity of C4+ hydrocarbons product.

Most of the available tools and methods applied in the design of chemical processes are not effective at the critical early stages of design when the process data is very limited. Businesses are often under pressure to deliver products in shorter times and this in turn prevents the evaluation of options. Early identification of options will allow for the development of an experimental program that will support the design process. The main objective of this work is to apply the Process Synthesis approach to develop a structured method of designing a process using mostly qualitative information based on limited experimental data, prior experience, literature and assumptions. Fischer-Tropsch (FT) synthesis of hydrocarbons from syngas generated by reforming natural gas and/or coal has been used as a case study to illustrate this method. Simple calculations based on experimental data and basic thermodynamics have been used to generate some FT Synthesis flowsheet models. The evaluation of different flowsheet models was done using carbon efficiency as a measure of process efficiency. It was established that when choosing the optimal region for the operation and design of an FT Synthesis process, the influence of the system parameters must be well understood. This is only possible if the kinetics, reactor, and process design are done iteratively. It was recommend not to optimize the reactor independent of the process in which it is going to be used without understanding the impact of its operating conditions on the entire process. Operating an FT Synthesis process at low CO per-pass conversions was found to be more beneficial as this will avoid the generation of high amounts of methane which normally results in large recycles and compression costs. Whether the process is run as a once-through or recycle process, the trend should be to minimize the formation of lighter gases by obtaining high Alpha values because carbon efficiency increases with the increase in value. Experiments should be performed to obtain process operating conditions that will yield high values. However, if the aim is to maximize diesel production by hydrocracking long chain hydrocarbons (waxes), then an optimal value should be targeted to avoid the cost of hydrocracking these very heavy waxes. The choice of the syngas generation technology has a direct impact on the carbon efficiency of an FT synthesis plant. This study has established that running an FT synthesis process with syngas obtained by steam reforming of natural gas with CO2 addition can yield high carbon efficiencies especially in situations were CO2 is readily available. In FT synthesis, CO2 is normally produced during energy generation and its emission into the environment can be minimized by using it as feed during the steam reforming of natural gas to produce syngas.

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.

In this work, inorganic membranes with highly dispersed metallic catalysts on macroporous titania-washcoated alumina supports were produced, characterized and tested in a catalytic membrane reactor. The reactor, operated as a contactor in the forced pore-flow-through mode, was used for the conversion of synthesis gas (H2 + CO) into mixed alcohols and hydrocarbons via the Fischer-Tropsch synthesis. Carbon monoxide conversions of 78% and 90% at near atmospheric pressure (300kPa) and 493K were recorded over cobalt and bimetallic Co-Mn membranes respectively. The membranes also allowed for the conversion of carbon dioxide, thus eliminating the need for a CO2 separation interphase between synthesis gas production and Fischer-Tropsch synthesis. Catalytic tests conducted with the membrane reactor with different operating conditions (of temperature, pressure and feed flow rate) on cobalt-based membranes gave very high selectivity to specific products, mostly higher alcohols (C2 – C8) and paraffins within the gasoline range, thereby making superfluous any further upgrading of products to fuel grade other than simple dehydration. Manganese-promoted cobalt membranes were found not only to give better Fischer-Tropsch activity, but also to promote isomerization of paraffins, which is good for boosting the octane number of the products, with the presence of higher alcohols improving the energy density. The membrane reactor concept also enhanced the ability of cobalt to catalyze synthesis gas conversions, giving an activation energy Ea of 59.5 kJ/mol.K compared with 86.9 – 170 kJ/mol.K recorded in other reactors. Efficient heat transfer was observed because of the open channel morphology of the porous membranes. A simplified mechanism for both alcohol and hydrocarbon production based on hydroxycarbene formation was proposed to explain both the stoichiometric reactions formulated and the observed product distribution pattern.

La presente tesis doctoral está centrada en la investigación de los parámetros estructurales que determinan las propiedades catalíticas en la síntesis de Fischer-Tropsch (SFT) de catalizadores de cobalto soportados en TiO2. Por un lado, el estudio de la influencia del polimorfo de óxido de titanio (rutilo vs. anatasa) utilizado como soporte en catalizadores de Co promovidos con Ru ha permitido obtener correlaciones entre la estructura cristalina del soporte, la extensión del efecto SMSI (interacción fuerte metal-soporte) y los resultados catalíticos. Por otro lado, mediante la modificación de las propiedades texturales del soporte TiO2-anatasa con el objetivo de obtener catalizadores con baja, media y alta área superficial se ha podido avanzar en el conocimiento del efecto SMSI y su correlación con las propiedades texturales del soporte. Además, las consecuencias del aumento en área superficial del soporte en la actividad y selectividad de catalizadores CoRu/TiO2 para la SFT se han podido explicar en base a las relaciones establecidas entre estructura y efecto SMSI. Adicionalmente, el uso de técnicas de luz sincrotrón junto con caracterización espectroscópica in situ realizada a presiones superiores a la atmosférica, ha permitido explicar el papel de la adición y concentración de Ru como promotor en catalizadores CoRu/TiO2. Finalmente, se han estudiado tratamientos de reducción-oxidación-reducción (ROR) en catalizadores CoRu/TiO2 con el objetivo de mejorar su actividad catalítica. Como conclusión general, los conocimientos derivados de los resultados obtenidos en esta tesis doctoral pueden aportar estrategias adecuadas para el diseño de catalizadores de FT mejorados basados en Co empleando TiO2 como soporte. / The present doctoral thesis focused on the investigation of the structural parameters that can determine the ultimate catalytic properties for Fischer-Tropsch synthesis (FTS) of TiO2-supported cobalt catalysts. On the one hand, the study of the influence of the titania polymorph (rutile vs. anatase) as support for Ru-promoted Co and Ru nanoparticles (NPs) has allowed to identify some correlations between the TiO2 crystalline phase, the SMSI (strong metal-support interaction) effect, and the catalytic performance for FTS of the catalysts. On the other hand, by preparing CoRu catalysts supported on TiO2-anatase with low, medium, and high surface area, further insights into the SMSI effect and its dependence on the textural properties of the TiO2-anatase support have been gained. Besides, the consequences of increasing the surface area of the support on the activity and selectivity of the catalysts for FTS have been explained based on the established structure-SMSI relationships. Moreover, a detailed study involving the use of in situ synchrotron-based spectroscopic characterizations at pressures higher than the ambient pressure usually applied in most previous works, has been carried out aiming at explaining the role of Ru addition and concentration as promoter in Co/TiO2 catalysts. Finally, reduction-oxidation-reduction (ROR) treatments have been applied on CoRu/TiO2 catalysts to revert the SMSI effect as a feasible strategy to enhance their catalytic activity. Overall, the results reported in this thesis provide grounds for designing TiO2-supported Co catalysts with improved activity and selectivity for FTS. / La present tesi doctoral està centrada en la investigació dels paràmetres estructurals que poden tenir influència en les propietats catalítiques dels catalitzadors que s'han aplicat a la reacció de síntesi de Fischer-Tropsch (SFT). S'ha estudiat la influència del polimorf de titani (rutil o anatasa) utilitzat com a suport de nanopartícules (NPs) de Co i Ru, observant correlacions entre l'estructura cristal·lina del suport, l'efecte SMSI (forta interacció metall-suport) i els resultats catalítics. D'altra banda, es va fer un estudi modificant les propietats texturals de la anatasa amb l'objectiu d'obtenir catalitzadors amb diferent àrea superficial, i s'ha pogut establir un coneixement més profund de l'efecte SMSI i la seua correlació amb les propietats texturals del suport. A més, la influència de l'augment de l'àrea superficial del suport per a la reacció de SFT, en termes d'activitat i selectivitat, han sigut explicats d'acord a les relacions establides entre l'estructura i l'efecte SMSI. Addicionalment, fent ús de tècniques de llum sincrotró juntament amb caracterització in situ realitzada a altes pressions, ha sigut possible explicar el paper de l'addició i concentració de Ru com a promotor en catalitzadors CoRu/TiO2. Finalment, s'han estudiat els tractaments de reducció-oxidació-reducció (ROR) en catalitzadors CoRu/TiO2 amb l'objectiu de millorar la seua activitat catalítica. En resum, els coneixements derivats dels resultats obtinguts en esta tesi doctoral permeten establir estratègies per al disseny de catalitzadors millorats per a la síntesi de FT basats en cobalt utilitzant TiO2 com a suport. / Bertella, F. (2018). Structural, promotion and metal-support interaction effects in Co/TiO2 catalysts for Fischer-Tropsch synthesis [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/107952 / TESIS