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

No description available.

The iron-catalysed hydromagnesiation of styrene derivatives has been developed further from previous publications, expanding the electrophile scope to enable the regioselective formation of new carbon-carbon and carbon-heteroatom bonds (Scheme A1). A commercially available pre-catalyst and ligand were used to give an operationally simple procedure that did not require prior synthesis of a catalyst. This work also investigated the hydromagnesiation of dienes, using a screen of ligands commonly used in transition metal catalysis. An investigation into the magnesium-catalysed hydroboration of olefins was also carried out. Although mostly unsuccessful, it was demonstrated that in the presence of a magnesium catalyst, a small amount of vinyl boronic ester could be formed from an alkyne (Scheme A2). Simple magnesium salts were also investigated for the reduction of carbonyls. Lastly, this work explored the titanium-catalysed hydrosilylation of olefins, using a novel activation method developed within the group (Scheme A3). The results were compared to those published previously using traditional organometallic activation methods and attempts at identifying conditions to improve chemoselectivity were carried out.

Much of the energy used in the United States and around the globe is obtained from petroleum, natural gas, and coal. Photocatalytic CO2 reduction can be used to transform CO2 to useful fuels and making fossil fuels more renewable. Input of energy is required, and the sun can provide the required energy for this transformation. Photosensitizer, catalyst, and electron donor are required for photocatalytic CO2 reduction. Due to lack of earth-abundant sensitizers, zinc dipyrrin complexes were synthesized by previous group members and have been used as photosensitizers in this research. The ground and excited state electrochemical properties of two zinc dipyrrin complexes were determined in polar and nonpolar solvents and the measured potentials were used to match the zinc sensitizers with an energetically appropriate iron porphyrin catalyst and a benzylthiol sacrificial electron donor. Lastly, pure CO2 gas was used as the source of carbon for the reduction of CO2 by photocatalysis with the zinc photosensitizers, iron catalyst and sacrificial electron donor. The products formed in headspace were analyzed by GC

ABSTRACT Nanostructured silica materials were synthesised by the sol-gel process using simple hydroxyacids as template precursors, and these materials were employed as supports for a low temperature iron Fischer-Tropsch (FT) catalyst. Thus, this thesis is divided into two parts: (I) the synthesis of nanostructured silica gels, and (II) their use as catalyst supports in the FT reaction. PART I The effects of synthesis conditions, acidic and basic template precursors and their amounts, synthesis temperature, duration of hydrolysis and ageing, solvent concentration, organic co-solvent, and the synthesis procedure used on the morphology of the silica materials were studied. The synthesised silica gels were characterised by TEM, SEM, BET, TGA, and XRD. Mixtures of different morphologies were obtained with all the hydroxyacids used and the studies revealed that the morphology of the resultant silica gels was largely determined by the type of the hydroxyacid used. The use of oxalic acid produced materials with 4-9 % micropores and a mixture of meso- and macropores mainly consisting of hollow tubes and hollow spheres; the use of D-gluconic and L-tartaric acids produced mesoporous materials mainly consisting of hollow spheres and sheets with folds, respectively; while the use of stearic and cinammic acids produced macroporous materials mainly consisting of solid spheres and undeveloped particles, respectively. The silica gels formed were found to be amorphous in nature, despite the different morphologies that existed in them, and were also thermally stable.Studies involving the use of oxalic and D-gluconic acids showed that the key to the shape of the resultant morphologies resided in the shape of the template crystals formed in solution under specific synthesis conditions. The template shape depended on the type of the template precursor (i.e. both the acid and the base) and its amount. It was also observed that under certain conditions, both at elevated temperatures (≥ 55 oC) and at high water concentrations (> 50 %), the template dissolved and this led to low yields of shaped morphologies (i.e. hollow spheres and tubes). The solvent concentration to produce a maximum tube yield (in the case of oxalic acid) and hollow sphere yield (in the case of D-gluconic acid) was found to require about 25- 50 % water. Very well-developed tubes were also obtained at this concentration (i.e. with oxalic acid). Long hydrolysis and ageing times (i.e. > 2 h) of the sols and gels, respectively, resulted in the formation of surface attached colloidal particles and of tubes and hollow spheres with decreased wall thicknesses. Pre-formation of the template prior to addition of TEOS produced materials with lower surface areas, higher tube yields and bigger tube sizes when compared with materials synthesised by forming the template together with the silica gel. PART II Two types of silica gels were used as supports for an iron FT catalyst; the nanostructured silica gels (tubes with surface area 109 m2/g and spheres with surface area 245 m2/g ) and a commercial silica gel (Davisil silica, surface area 273 m2/g - consisting of undeveloped particles). The effect of varying the potassium promotion levels and of the support morphology on the catalyst activity and selectivity in the FT reaction was studied at 250 oC, in a slurry operated CSTR.It was observed that an increase in the potassium loading up to 0.5 wt % in the Davisil silica catalyst led to a decrease in the catalyst FT and water gas shift (WGS) activity, and methane selectivity. However, the efficiency of the catalyst to produce hydrocarbons increased with an increase in potassium loading up to 0.5 wt %. Increasing the potassium level up to 0.9 wt % led to a slight increase in both the catalyst activity and methane selectivity, and a decrease in the catalyst efficiency. For the silica tubes catalyst, increasing the potassium loading to 0.5 wt % led to an increase in the catalyst activity and methane selectivity, while increasing the potassium level up to 0.9 wt % led to a decrease in the catalyst activity. For both supports, increasing the potassium loading led to an increase in the selectivity towards high molecular weight hydrocarbons, olefins (relative to paraffins) and terminal olefins (relative to internal olefins). While the Davisil silica and the silica tube catalysts remained more or less stable throughout the reaction, the activity of the silica spheres catalyst declined rapidly with time. The nanostructured silica gel supported catalysts both showed higher activities and methane selectivities, but lower efficiencies when compared to the Davisil silica catalyst. Although the selectivity of all three catalysts towards olefins were similar, their selectivity towards high molecular weight hydrocarbons decreased in the order Davisil silica > silica spheres > silica tubes. Elongated needlelike Fe nanoparticles (NPs) were obtained in the silica tubes catalyst, semi hexagonal Fe NPs were formed in the silica spheres catalyst, while the Fe NPs could not be distinguished from the support in the Davisil silica catalyst. After the reaction, the surface areas of all three catalysts were found to have decreased and the catalysts to have sintered. The nanostructured silica supported catalysts showed the presence of Fe nanozones surrounded by a layer of amorphous carbon, while only agglomerated particles of Fe and some carbon rich regions were observed in the Davisil silica catalyst. No evidence of alteration of the morphology of the nanostructured silica supports was observed after the reaction.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Este trabalho teve como objetivo sintetizar catalisadores metÃlicos de ferro suportados em carbono ativado a base de polÃmeros para sÃntese de Fischer-Tropsch. A preparaÃÃo dos catalisadores foi realizada pelo mÃtodo de impregnaÃÃo a umidade incipiente, utilizando soluÃÃo aquosa de nitrato de ferro nonahidratado para obtenÃÃo de amostras com, aproximadamente, 55% de ferro. Duas amostras foram preparadas (FeCP1 e FeCP2) e caracterizadas por fluorescÃncia de raios-X por energia dispersiva (EDXRF), difraÃÃo de raios-X (DRX), medidas de fisissorÃÃo de nitrogÃnio, espectroscopia fotoeletrÃnica de raio-X (XPS), microscopia eletrÃnica de varredura (SEM-EDS) e reduÃÃo à temperatura programada (TPR). As amostras foram submetidas tambÃm a testes catalÃticos, utilizando-se diferentes condiÃÃes de temperatura (513, 528 e 543 K), pressÃo (20, 25 e 30 atm) e razÃo molar H2:CO de 1 e 0,5. Os dados de EDXRF evidenciaram considerÃvel diferenÃa no teor de metal impregnado entre os dois catalisadores; o FeCP2 apresentou teor prÃximo ao esperado enquanto o catalisador FeCP1 ficou aquÃm do desejado. Os difratogramas obtidos por DRX mostraram um maior grau de cristalinidade da amostra FeCP2, enquanto FeCP1 e os dois suportes (CP1 e CP2) apresentaram-se como semi-cristalinos. Para o catalisador FeCP2, apresentaram-se duas fases ativas presentes, α-Fe2O3 e γ-Fe2O3; jà no FeCP1, hà apenas α-Fe2O3. A anÃlise das caracterÃsticas texturais revelou que, apÃs a introduÃÃo metÃlica no suporte, houve decrÃscimo nos valores de Ãrea especÃfica, volume de poros e diÃmetro de poros, sendo mais perceptÃvel para o catalisador FeCP2. As curvas de XPS expuseram os grupos funcionais oxigenados presentes na superfÃcie dos suportes, bem como a presenÃa do Fe+3 como fase ativa predominante em ambos os catalisadores. O espectro de ambos os catalisadores apresentou tambÃm um pico satÃlite que sugere a presenÃa de um outro estado de valÃncia do ferro semelhante ao que se tem no carbeto de ferro. As imagens obtidas por SEM exibiram forma e superfÃcie irregulares, sendo as partÃculas presentes no FeCP2 maiores que a do FeCP1 devido a sua cristalinidade. Os dados de EDS demonstraram que, aproximadamente, metade do percentual de ferro presente no catalisador encontra-se na superfÃcie. Pode-se inferir tambÃm por essa anÃlise, utilizando-se seu espectro, a presenÃa de carbeto de ferro na superfÃcie do catalisador. As curvas de TPR evidenciaram uma maior estabilidade do catalisador FeCP2 mediante o FeCP1, por este ter apresentado trÃs etapas de reduÃÃo do Ãxido de ferro e nÃo duas, como apresentada para aquele Ãltimo. O teste catalÃtico expÃs a melhor eficiÃncia do catalisador FeCP2 para a produÃÃo de hidrocarbonetos na faixa de C5-C9, para as mesmas condiÃÃes de temperatura, pressÃo e razÃo molar. Entretanto, a diminuiÃÃo da razÃo molar desfavoreceu a obtenÃÃo de hidrocarbonetos pesados. / The aim of this work was to synthesize iron catalysts supported on polymer-based activated carbons, for the Fischer-Tropsch synthesis. The preparation of the catalysts was performed by incipient wetness impregnation method using an aqueous solution of iron nitrate nonahydrate to obtain samples with approximately 55 % of iron. Two samples were prepared (FeCP1 and FECP2) and characterized by energy dispersive X-ray fluorescence (EDXRF), X-ray diffraction (XRD), nitrogen adsorption measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM-EDS) and temperature-programmed reduction (TPR). The samples were also submitted to catalytic tests using different conditions of temperature (513, 528 and 543 K), pressure (20, 25 and 30 atm), and H2:CO molar ratio of 1 and 0.5. EDXRF data showed considerable difference in content of impregnated metal for both catalysts. FeCP2 exhibited an iron load close to the value expected while FeCP1 presented an iron load significantly lower than expected. XRD patterns showed a higher degree of crystallinity of the sample FeCP2, whereas FeCP1 and both supports used (CP1 and CP2) were found to be semi-crystalline. FeCP2 catalyst presented two active phases, α-Fe2O3 and γ-Fe2O3, while FeCP1 showed only one phase, α-Fe2O3. The analysis of the textural characteristics revealed a decrease in the values of the specific area, pore volume and pore diameter after the introduction of the metal into the support, which was more noticeable with the FeCP2 catalyst. XPS patterns indicated oxygen functional groups on the support surface and the presence of Fe+3 as the predominant active phase on both catalysts. The spectrum of both catalysts also showed a satellite peak which shows the presence of another valence state similar to the iron carbide. Images obtained by SEM revealed irregular shape and surface, being the particles present in FeCP2 greater than those on FeCP1 due to the crystallinity of the former. EDS data showed that approximately half of the iron percentage present in the catalyst bulk is on the surface. The presence of iron carbide on the catalyst surface can be inferred by using this spectrum analysis too. TPR graphics demonstrated a higher stability of the FeCP2, due to the three-step reduction of iron oxide instead of two as shown for the FeCP1. According to the results of the catalytic tests FeCP2 exhibited a better efficiency for the production of hydrocarbons in the C5-C9 range, for the same conditions of temperature, pressure and molar ratio. However, the decrease in the molar ratio disfavors the production of heavy hydrocarbons.

Orientadores: Christiane de Arruda Rodrigues, Rodnei Bertazzoli / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-18T16:59:20Z (GMT). No. of bitstreams: 1 Moraes_JulianaPiresde_M.pdf: 2352216 bytes, checksum: 36449200a80f1740bb7e26db1412d9de (MD5) Previous issue date: 2011 / Resumo: Na indústria de cloro-soda, há um crescente interesse no desenvolvimento de tecnologias que resultem numa redução do consumo de energia destinado ao processo de produção de cloro. As células eletroquímicas empregadas no processo cloro-soda são: Mercúrio, Diafragma e Membrana. Atualmente está havendo uma substituição progressiva dos processos empregando mercúrio e difragma por células com membranas trocadoras de íons, pois este processo apresenta melhor eficiência, menor gasto energético e a não geração de resíduos tóxicos. O objetivo deste trabalho envolve a aplicação de eletrodos de difusão gasosa (EDG) modificado com catalisador ferro para a redução do oxigênio, visando à otimização da produção de cloro e maior economia energética nos processos de cloro-soda. Na produção do EDG empregou-se a adição de catalisador ferro nas seguintes proporções: 5%, 10%, 15% e 20% (m/m) em relação à massa de carbono Printex 6L. Duas granulometrias de partículas do catalisador Fe foram empregadas para o preparo dos eletrodos. Ensaios voltamétricos foram realizados para avaliar o efeito da introdução do catalisador de Fe no EDG na reação de redução do oxigênio, além de identificar qual a melhor concentração de Fe e granulometria do catalisador. Os ensaios de voltametria foram realizados em uma célula de compartimento único na temperatura de 25 ºC e solução de trabalho NaOH 320 g/L. Em seguida, ensaios de eletrólises foram realizados para avaliar o desempenho dos EDG, modificado ou não com catalisador Fe, na geração de cloro e DDP da célula, empregando as melhores condições de operação encontradas nos estudos voltamétricos. Os ensaios de eletrólise foram realizados em uma célula com dois compartimentos, separados por uma membrana catiônica Náfion® N242. Nos ensaios de eletrólise foi utilizada uma solução de NaOH 320 g/L, com temperatura de 25 ºC, no compartimento catódico e no compartimento anódico, uma solução de NaCl 250 g/L com temperatura de 70 ºC. A condição de trabalho que apresentou maior redução do consumo de energia e maior geração de cloro foi empregando o EDG com 10% Fe com tamanho de partículas em torno de 0,16 mm2. Comparado ao EDG sem catalisador, verificou-se uma redução no gasto energético de aproximadamente 66%. Isto comprova que o metal de transição Fe atua como o centro ativo e que a atividade eletrocatalítica depende principalmente das propriedades redox do eletrodo modificado / Abstract: The interesting in the developing of technologies that contribute in a reduction of energy consumption in chlor-alkali process is growing. The electrochemical cells used in production of chlorine area: Mercury, Diaphragm and membrane. Currently, the mercury and diaphragm cell have been replaced for membrane technology because this cell is more efficient, presents low energy consumption and does not generate toxic waste. The main of this work involves the investigation the performance of gaseous diffusion electrodes modified with particles of iron, for reduction of oxygen in the production of chorine during the electrolysis of brine. In preparing the cathodes of diffusion of oxygen, was used a mass precursor, composed of carbonaceous pigment Printex and suspension of the PTFE powder. The catalyst was introduced in form of Fe metal power in the following percentages: 5%, 10%, 15% e 20% (m/m). For sintering of the electrode of gaseous diffusion (GDE) was weighed 0.2 g of mass precursor and placed on the mold. The mold was heated to a temperature of 340ºC for the sintering of the electrode, under pressure of 146 Kgf/cm2 for 2 hours. After sintering, the electrodes were tested for permeability. In next stage, the electrodes of gaseous diffusion were used in voltammetric studies to examine the influence of catalyst in the reactions of reduction of oxygen in the GDE and identify the best grain size and percentage of iron in electrode. Then, the tests were performed using a single cell compartment, with the type DSA® as counter electrode and the Ag/AgCl as reference electrode in 320 g/L NaOH solution at 25ºC. After, the electrolysis were performed using constant current electrolysis to the GDE or pyrolytic graphite as cathode and DSA® as anode. These tests were carried out in a cell with two compartments, separated by a membrane cationic Nafion N242. The anolyte was a solution of 250 g/L NaCl at 70 ºC and the catholyte was a solution of 320 g/L NaOH, at 25 ºC. During the electrolysis the chorine dissolved in the form of hypochlorite and chlorine gas were quantified by iodometry titration. The electrode that had a better performance in chlorine generation and lower energy consumption was modified with Fe 10% (m/m) with small particle size. This electrode shown around 66% reduction of energy consumption when compared to GDE without iron metal catalyst. This behavior proves that the transition metal Fe acting as the active center and that the electrocatalytic activity depends mainly on the redox properties of the modified electrode / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

The purpose of this research is to examine the effect of iron catalyst thickness on the straightness of growth of carbon nanotube microelectromechanical systems (CNT-MEMS). One of the key benefits of CNT-MEMS is that they can potentially have very high aspect ratios. One of the challenges in attaining these high aspect ratios is maintaining device straightness; as these devices get taller, the edges tend to curve rather than grow straight vertically. Scanning electron mi- croscope images of samples grown using various iron catalyst thicknesses show that both straight growth and relatively good edge definition can be achieved using iron thicknesses between 7 and 8 nm. Below this thickness, individual CNT are well-aligned, but CNT forests are not necessarily straight. Above this thickness, the CNT forests are relatively straight, but individual CNT are not well-aligned and edge definition is very poor. Iron availability for CNT growth is also affected by a device's or feature's proximity to other regions of iron. By using an iron catalyst thickness ap- propriate for straight growth, and by adding borders of iron around features or devices, a designer can greatly improve straightness of growth for CNT-MEMS.

This work investigates a novel iron Fischer-Tropsch (FT) catalyst preparation and describes the development of a trickle fixed-bed recycle reactor model (TFBRRM) for the FT synthesis applicable to both iron and cobalt catalysts. The iron catalyst preparation was developed using a novel solvent deficient precipitation reaction. Fifteen Fe/Cu/K/SiO2 catalysts were prepared to investigate key preparation variables including timing of promoter addition, washing or not washing after precipitation, and drying temperature. Adding promoters to starting materials before precipitation (1S) gives more uniform promoter distributions which gives higher water-gas shift activity and lower methane selectivity. Unwashed catalysts have smaller average pore and crystallite diameters (3.9-10.8 nm versus 15.3-29.5 nm) and 30% smaller pore volumes, but 65% higher rates of reaction than washed catalysts. Catalysts dried first at 100 °C have up to 50% smaller average pore and crystallite diameters, but 10-20% higher rates of reaction than catalysts dried first at 60 °C. Overall, 1S catalysts, left unwashed, and dried first at 100 °C are best suited in activity, selectivity, and stability for wax production from hydrogen-deficient feed stocks such as coal, biomass, or municipal waste. The activity of the most active catalyst of this study is greater than or equal to the activities of two of three catalysts reported in the literature. This dissertation describes in detail the TFBRRM, reports its validation, and presents results of varying fundamental, theoretically-based parameters (e.g. effective diffusivity, Prandtl number, friction factor, etc.) as well as physical process parameters (i.e. recycle ratio, pressure, flow rate, tube diameter, cooling temperature, and pellet diameter and shape). For example, the model predicts that decreasing effective diffusivity from 7.1E-9 to 2.8E-9 m^2/s results in a lower maximum temperature (from 523 to 518 K) and a longer required bed length to achieve 60% conversion of CO (from 5.7 to 8.5 m). Using the Tallmadge equation to estimate friction losses as recommended by the author results in a pressure drop 40% smaller than using the Ergun equation. Validation of the model was accomplished by matching published full-scale plant data from the SASOL Arge reactors.

Den internationella medvetenheten om hotet med växthusgaser har bidragit till en prioriterad utveckling av alternativa och rena tekniker baserade på förnybara i stället för fossila bränslen. Biomassaförgasning är en teknik för framställning av icke-fossil energigas från biomassa. Den har flera tillämpningsområden, vilket bland annat inkluderar kraftgenerering genom förbränning i motorer. Ett av huvudproblemen med denna teknik är produktionen av tjärföreningar under processen. Detta leder till ett behov av ett gasrenings- och uppgraderingssteg med hjälp av en katalytisk bäddreaktor, vilket ökar kostnaderna och minskar den termiska effektiviteten. Nickel är den vanligast använda katalysatorn för ångreformering, men den är tyvärr giftig. I detta projekt studeras järn, som ett alternativ till nickel. Järn är miljövänlig, giftfri och mer rikligt förekommande jämfört med nickel. Specifikt så användes ett sintrat järnpulver tillverkat av Höganäs AB, Sverige, med toluen som en modellförening för tjära. För att förstå hur oxidationen av järn och järnoxider fungerar mer i detalj under den katalytiska omvandlingen så utfördes testerna med ånga och toluen en temperatur av 750°C och ett tryck av 1 bar. I experimenten observerades att ju större mängd ånga som tillfördes till reaktorn, desto fler problem observerades under katalytiska processen. Den negativa effekten av oxidationen av järnkatalysatorn var mycket större än de fördelar som ånga normalt har på den katalytiska processen. / The international community’s awareness of the danger of greenhouse gases has contributed to prioritising the development of alternative and clean technologies, using renewable sources, over fossil fuels. Biomass gasification is a technology for the production of non-fossil synthesis gas from biomass. It has numerous applications including power generation through combustion in engines. One of the main problems with this technology is the production of tars during the process. This leads to the need to implement a gas cleaning and upgrading step using a catalytic bed reactor, which increases costs and reduces thermal efficiency. nickel is the common catalyst for steam reforming but it is toxic. Therefore, to overcome these drawbacks and to be environmentally friendly, iron, a non-toxic and more abundant catalyst, was used in this project. Specifically, sintered iron powder manufactured at Höganäs AB, Sweden, was used and toluene was taken as the model tar compound.  To understand the iron reactions in more detail, namely the behaviour of iron oxidation during re- forming, the toluene tests were carried out with steam as gasification agent at a temperature of 750°C and pressures below 1 bar. In the experiments, it was observed that the higher the amount of steam in the reactor, the more problems were observed in the catalyst. The negative effect of the oxidation of the catalyst far outweighed the benefits that steam could have on the catalysis.