The present thesis concerns catalytic conversion of syngas (H2+ CO) into a blend of methanol and higher alcohols, an attractive way of producing fuels and chemicals. This route has the potential to reduce the oil dependence in the transport sector and, with the use of biomass for the syngas generation, produce CO2-neutral fuels. Alkali promoted MoS2-based catalysts show a high selectivity to higher alcohols, while at the same time being coke resistant, sulfur tolerant and displaying high water-gas shift activity. This makes this type of catalyst especially suitable for being used with syngas derived from biomass or coal which typically has a low H2/CO-ratio. This thesis discusses various important aspects of higher alcohol synthesis using MoS2-based catalysts and is a summary of four scientific papers. The first part of the thesis gives an introduction to how syngas can be produced and converted into different fuels and chemicals. It is followed by an overview of higher alcohol synthesis and a description of MoS2-based catalysts. The topic alcohol for use in internal combustion engines ends the first part of the thesis. In the second part, the experimental part, the preparation of the MoS2-based catalysts and the characterization of them are handled. After describing the high-pressure alcohol reactor setup, the development of an on-line gas chromatographic system for higher alcohol synthesis with MoS2 catalysts is covered (Paper I). This method makes activity and selectivity studies of higher alcohol synthesis catalysts more accurate and detailed but also faster and easier. Virtually all products are very well separated and the established carbon material balance over the reactor closed well under all tested conditions. The method of trace level sulfur analysis is additionally described. Then the effect of operating conditions, space velocity and temperature on product distribution is highlighted (Paper II). It is shown that product selectivity is closely correlated with the CO conversion level and why it is difficult to combine both a high single pass conversion and high alcohol selectivity over this catalyst type. Correlations between formed products and formation pathways are additionally described and discussed. The CO2 pressure in the reactor increases as the CO conversion increases, however, CO2 influence on formation rates and product distribution is to a great extent unclear. By using a CO2-containing syngas feed the effect of CO2 was studied (Paper III). An often emphasized asset of MoS2-based catalysts is their sulfur tolerance. However, the use of sulfur-containing feed and/or catalyst potentially can lead to incorporation of unwanted organic sulfur compounds in the product. The last topic in this thesis covers the sulfur compounds produced and how their quantity is changed when the feed syngas contains H2S (Paper IV). The effect on catalyst activity and selectivity in the presence of H2S in the feed is also covered. / <p>QC 20150115</p>

Promoter effects on SBA-15 supported iron Fischer-Tropsch catalysts were investigated for their potential to improve high temperature catalyst performance. FTS catalysts promoted by manganese (0.15%-1.4%), copper (0.15%-1%), and potassium (0.5%-3%), with all percentages stated on the basis of mass percentage of final catalysts, were prepared and tested at 430°C and ambient pressure in a fixed bed reactor. Manganese showed the ability to promote the FT reaction, increasing both the CO conversion and the average chain length of hydrocarbon products. Compared to the unpromoted catalyst composed only of iron supported on SBA-15, 1.4%Mn (mass) promotion of 15% (mass) iron on SBA-15 improved CO conversion from 29% to 32%, increased alpha from 0.21 to 0.34, decreased carbon dioxide selectivity from 76% to 50%, increased C2-C4 selectivity from 9.6% to 30% and increased C5+ selectivity from 0.21% to 2.2%. Copper promotion gave increased conversion, but did not significantly affect alpha or carbon dioxide selectivity. Potassium promotion in the range of 0.5% to 3% by mass, on the other hand, had a negative effect on CO conversion at all concentrations tested.

The focus of this research was to investigate the role of carbon nanotubes as active catalysts in the Fischer-Tropsch reaction to derive liquid fuels from synthesis gas. Carbon nanotubes (CNTs) have unique structural and mechanical properties that make them ideal catalyst supports, but they also exhibit catalytic potential as well. This study implored the use of multi-walled CNTs on different substrates and single-walled CNTs grown from various precursors to analyze the effectiveness of the CNTs in FT synthesis. Multi-walled nanotubes (MWNTs) were tested on two different substrates: alumina pellets and inconel. The MWNTs on the alumina substrate yielded nearly all alkane and alkene products, with very little aromatic products. The amount of converted syngas reached 97% but had a high liquid product selectivity to methane, at roughly 57%. The MWNTs on inconel substrate produced nearly 80% aromatic products in one stage of the experiment, while the other three stages produces almost all alkane products with little oxygenates. Much of the liquid product yield (upwards of 73%) was between C10 and C21, which is ideal for diesel fuel. Single-walled nanotubes (SWNTs) were also tested in the FTS. All of the SWNTs were tested under a series of 6 temperatures, 300psig, and a syngas ratio of 1:1. Iron, nickel, and cobalt, which have all been proven as effective FT catalysts, were tested in trace amounts with CNTs. Fe-SWNTs (ferrocene assisted SWNTs) yielded a product of 100% C7 and C8 carbon species at two of the temperatures while 3 of the temperatures held a combination of longer chained alkanes, of C18 and longer. However, the last temperature converted 100% of the feedgas into methane and CO2. The product selectivity to CH4 and CO2 posed a problem with the Fe-SWNTs catalyst, where in all temperatures the selectivity exceeded 80%. Ni-SWNTs (nickellocene assisted SWNTs) yielded slightly better results with a higher selectivity to C2-C7, but no selectivity to longer chained hydrocarbons. Co-SWNTs (cobaltocene assisted SWNTs) tested under the same parameters yielded similar results as the Fe-SWNTs, with a very high selectivity to CH4 and CO2. Only at temperatures of 300 and 250°C were there any selectivity to compounds other than CH4 and CO2, but less than 10% selectivity to those alkanes (C2+). The final experiment consisted of a catalyst prepared from a feed solution containing a mixture of ferrocene and nickellocene. The Fe+Ni-SWNT catalyst underwent the same conditions as the other SWNT catalysts, this combination yielded favorable results with over 98% conversion of syngas over all temperatures and a high selectivity to shorter chain length hydrocarbons, namely alkanes of chain lengths between C2 and C7. Although the higher temperatures did show a selectivity to methane (roughly 45%), the CO2 selectivity was rather low, below 10% (except at 450°C, which pushed 20%).

Orientador: Maria Regina Wolf Maciel / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-16T03:15:43Z (GMT). No. of bitstreams: 1 Peres_AnaPaulaGimenez_M.pdf: 2893498 bytes, checksum: 660e046de1120b97974948724435b696 (MD5) Previous issue date: 2010 / Resumo: Biodiesel (alquil éster) é um combustível limpo derivado de fontes renováveis, óleos vegetais ou gordura animal. Sabe-se que, aproximadamente, 10% em peso do óleo vegetal utilizado como insumo na produção de biodiesel é convertido em glicerina, de forma que existem grandes incentivos para a utilização deste subproduto. A pirólise da glicerina residual por sua vez é um processo com grande potencial para a produção de biocombustíveis como hidrogênio (H2) e gás de síntese (matéria prima para produção de combustíveis sintéticos via reação de Fischer-Tropsch) gerando portanto, produtos de alto valor agregado. Assim, neste trabalho, a pirólise foi realizada em um reator de leito fixo utilizando-se glicerina comercial e glicerina residual da produção de biodiesel dos Laboratórios de Otimização, Projeto e Controle Avançado (LOPCA) e de Desenvolvimento de Processos de Separação (LDPS). Primeiramente, foram realizados planejamentos fatoriais fracionários para a determinação das variáveis independentes (temperatura e tempo de reação, vazão de gás de arraste e volume de glicerina) mais significativos no processo. Sendo que o volume de glicerina foi a variável com menor significância, portanto foi excluída do processo. Posteriormente, realizaram-se os experimentos de acordo com o planejamento fatorial completo 23 (com mais três pontos centrais). Foram obtidos dois modelos codificados de primeira ordem que descrevem a conversão de glicerina residual em hidrogênio e gás de síntese em função da temperatura de reação, tempo e vazão de gás de arraste. De acordo com as condições advindas da aplicação da metodologia de superfície de resposta, altas conversões de glicerina em H2 e em gás de síntese, em torno de 45% mol/mol e 80% mol/mol, respectivamente, foram experimentalmente obtidas em: 850ºC, 30min e vazão do gás de arraste 50mL/min. No processo de pirólise da glicerina foram obtidos produtos líquidos, gasosos e cinzas. Em média, obtiveram-se conversões superiores a 85% v/v de glicerina para produtos gasosos, entre eles H2 e CO (gás de síntese) em maior quantidade. Além desses gases, foram encontrados CO2, metano, etileno, etano e propano. Já os produtos líquidos foram basicamente acetaldeído, acetona, metanol e etanol. Através dos cálculos de energia ficou claro que a produção de H2 a partir desse processo é viável energeticamente. Sendo que para um mol de glicerina processada a energia líquida da reação foi 293kJ. / Abstract : Biodiesel (alkyls esters) is a clean burning fuel derived from renewable lipid feedstock such as vegetable oil or animal fat. Glycerin is a by-product from the biodiesel production which represents nearly 10% of product total mass. As the biodiesel production is increasing there exist incentives to use the glycerin as raw material for other processes. The glycerin pyrolysis is a promising way to produce biofuels such as hydrogen and syngas (feedstock used in synthetic fuels production via Fisher-Tropsch reaction) and at same time avoids its accumulation in the environment. Glycerin pyrolysis was carried out in a fixed bed reactor filled with silica-quartz and/or alumina oxide. The raw material considered in this work was pure glycerin and crude glycerin from biodiesel production. Experimental designs were carried out in specific conditions to identify the impact of the main process variables. At first, a fractional factorial experimental design was chosen to analyze the most significant factors (reaction temperature, reaction time, glycerin quantity and flow rate of carrier gas) on the conversion glycerin to hydrogen and syngas. The glycerin quantity was the least significant factor, so it was excluded from further investigation. Afterwards, the experiments were carried out according to a 23 complete factorial design plus three central points. Two first-order models were obtained to predict the crude glycerin conversion in hydrogen and syngas as a function of reaction temperature, reaction time and flow rate of carrier gas. From the surface methodology analysis, high conversions of glycerin into hydrogen and syngas, around 45% mol/mol and 85% mol/mol, respectively, can be obtained under the following conditions 850 º C, 30 min and flow carrier gas, 50ml/min. The best glycerin conversion to gas products was 80% v/v of glycerin. The main gás products were H2 and CO. Besides these gases, CO2, CH4, C2H4 and C3H8 were also obtained in smaller proportions. The liquid product compositions were methanol, ethanol, acetone and acetaldehyde. Through the energy calculations, it becomes clear that production of H2 from this process is energetically feasible. For one mole of glycerol, computed net energy of the reaction was around 293kJ. / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

Gasification is a promising technique for transforming solid biomass into a gas that can be used to produce renewable heat, power, fuels or chemicals. Biomass materials, such as forestry residues, can be high moisture, heterogeneous mixtures with low bulk density - properties that make them difficult to handle and convert. Consequently, this means that feedstock pre-treatment is usually necessary in order to facilitate its conversion by gasification. Pre-treatments methods, which include comminution, drying, pelletization, torrefaction, or carbonization will affect the properties of the biomass which will affect their gasification in a fluidized bed. The objective of this thesis was to determine how biomass pre-treatment can influence gasification in a fluidized bed. A single forestry residue was processed using five pre-treatment process levels: sieving (as a surrogate for comminution), drying (moisture content), pelletization, torrefaction, and carbonization. The fractions derived from these processes were gasified in a small pilot-scale air blown bubbling fluidized bed gasifier (feed rate 8 – 25 kg/h). The particle size and form had an impact on the gas composition, tar content, and cold gas efficiency of the gasification. Over the conditions tested, the finest fraction produced a gas with a H2/CO ratio of 0.36 – 0.47 containing 7 – 59 g/m3 tar (gravimetric) at a cold gas efficiency of 30 - 41%. The pellets on the other hand yielded a gas with a H2/CO ratio of 0.89 - 1.14, containing 3 – 37 g/m3 tar (gravimetric) at a cold gas efficiency of 41 – 60%. Drying, torrefaction and carbonization also had an impact on the gasification performance. Carbonization was able to reduce the yield of tar (as measured by gas chromatography) by more than 95% relative to the parent material. Finally, four different forestry residues were gasified in a large pilot-scale bubbling fluidized bed with air and steam-oxygen mixtures (feed rate 200 – 245 kg/h) in order to assess whether the comminution effect could be observed at the large scale. One feedstock with a significant portion of small particles showed the expected effects compared to the feed materials with large feed particles: lower H2/CO ratio, greater tar yield, lower cold gas efficiency while the other feed material containing a substantial amount of small particles did not show these effects.

Future predicted shortages in fossil fuel resources and environmental regulations from fossil fuel combustion have led to great research interest in developing alternatives to fossil fuels. Biomass-derived bio-oils will have the potential to replace conventional transportation fuels because of their sustainability and environmental advantages. However, the presence of high percentages of chemical oxygenates cause negative properties such as high water content, low volatility, lower heating value, corrosiveness, immiscibility with fossil fuels and instability during storage and transportation. Moreover, polymerization, esterification, condensation and other reactions occur between these highly reactive oxygenates in bio-oil (Diebold 2000). These negative properties hinder both bio-oil direct use as a fuel and the fuel conversion process (Mohan, et al. 2006). Hydrodeoxygenation has proven itself effective in converting of bio-oil to pure hydrocarbons. However, the large consumption of expensive hydrogen prevents the industrialization of bio-oil. Therefore, development of more efficient hydrodeoxygenation approaches with less capital cost will be desirable. The objective of this current research was to upgrade raw and distilled bio-oil by oxidation to a stabilized precursor to the final hydrocracking step of hydrodeoxygenation. In the second chapter, raw bio-oil, two pretreated bio-oils and hydrotreated bio-oil were hydrodeoxygenated to produce liquid hydrocarbons in the continuous reactor. In the third chapter, raw bio-oil, oxidized raw bio-oil, distilled bio-oil and oxidized distilled bio-oil were hydrodeoxygenated to liquid hydrocarbons with hydrogen in the batch reactor. In the fourth chapter, oxidized distilled bio-oil was hydrotreated with model syngas to organic liquid products followed by hydrocracking with hydrogen to produce liquid hydrocarbons. In the fifth chapter, oxidized distilled bio-oil was upgraded with syngas (H2/CO molar ratios of 4:6) in a single stage to produce organic liquid products. The resultant stabilities of these organic liquid products were investigated by application of accelerated aging. The research results showed that oxidized distilled bio-oil could be upgraded by the syngas in a single stage to produce stabilized bio-oil. This success will replace hydrogen by syngas for first stage hytrotreating and save shipping fee by transportation less weight of upgraded bio-oil rather than the bulky and high moisture content biomass.

No description available.

Gas turbines integrated with biomass gasification in a combined cycle power plant (Bio-IGCC) provide a path to power production with very high efficiency. Over 60% fuel-to-power efficiency has been demonstrated with natural gas. The fast ramp and relatively low cost make Bio-IGCC via gas turbines the ideal complement to intermittent power from wind turbines and PV cells. With stricter pollutant regulations and in order to promote the use of renewable fuels there is a great interest in improving fuel flexibility. An important feature of biomass gasification is that its properties vary depending on the feedstock and gasification principle and that the combustion characteristics are significantly different from conventional fuels. This makes it interesting to develop CFD models that can be used to simulate the combustion of syngas in existing gas turbines and for design optimization of new gas turbines.  The TECFLAM swirl burner geometry, which is designed to be representative of common gas turbine burners, was selected for an assessment of the differences between a typical hydrocarbon fuel and syngas. A two-stage approach was employed with development and validation of an advanced CFD model. The validated model was used to compare the flame shape and other characteristics of the flow between methane, 40% hydrogen enriched methane and four typical syngas compositions. The syngas compositions used are representative of practical gasification processes and biomass feedstocks. It was found that the syngas fuels experience lower swirl intensity due to high axial velocities that weaken the inner recirculation zone. A strong correlation was found between the laminar flame speed and the flame shape.  The simulation of a typical combustion geometry with syngas is quite demanding and requires a long computational time. In order to speed up the parametric analysis and to make it possible to test more configurations a Two-Step, One Way coupled method was assessed. This is a common approximation in CFD that is used to solve complex problems with limited computational resources. The test case used for the assessment was the CeCOST burner that uses strong swirl for flame stabilization. Only isothermal flow was investigated to eliminate the influence from flow – chemistry interactions. This method effectively divides the domain in two parts, one downstream and one upstream. The assumption behind this method is that the downstream part should not have a big influence on the upstream part and hence it could be solved separately. From the comparison it was found that the full solution and the approximations were in good qualitative agreement. However, there were some minor quantitative discrepancies, and it was proposed that the explanation for the differences could be the slightly different solution approaches that were used for the full simulation (URANS) and the two approximate solutions (RANS). The speed-up from using the approximate method was close to one order of magnitude.  However, because an artificial steady inlet cannot reproduce all the dynamic phenomena created by a swirler, for the continuation a full CeCOST domain was used. LES modelling was also employed to be able to identify smaller structures that would affect flame stability. Using LES and the Artificially Thickened Flame model, a syngas composition that relates to Black Liquor gasification was modelled. The flame front position using the CH2O mole fraction was estimated and it correlated well with the position estimated by the progress variable. The flame front position found by using the OH mole fraction was different to the two previous ones, predicting the hot part of the flame.

The emergence of biomass based energy warrants the evaluation of syngas from biomass gasification as a fuel for personal power systems. The objectives of this study were to determine the performance and exhaust emissions of a commercial 5.5 kW generator modified for operation with 100% syngas at different syngas flows and to compare the results with those obtained for gasoline operation at same electrical power. Maximum power output for gasoline operation was 2451 W and maximum power output for syngas operation was 1392 W. Overall efficiencies of the generator were same at maximum electrical power outputs for operation with both the fuels. At four different electrical power output categories, the exhaust concentrations of carbon monoxide and oxides of nitrogen were significantly lower while the carbon dioxide emissions were significantly higher for the syngas operation. The unit cost of electricity generation was $6.38/kWh for syngas operation and $0.56/kWh for gasoline operation.

No description available.