ABSTRACT This thesis presents the results of investigations regarding the effect of supercritical CO2 on the long term activity, life and deactivation rates of an Fe-Zn-K catalyst during Fischer Tropsch Synthesis from syngas (H2:CO =1:1) typically produced from coal gasification. Previous studies at SIUC on FTS in Supercritical CO2 (SC-CO2) have shown that CH4 selectivity was inhibited and with the presence of excess CO2, the WGS reaction was reversed. This increased the carbon economy as result of the reduction in parasitic loss of CO to CO2. In addition, it was observed that the conversion of CO, under these pressures and CO2 dilution, was significantly enhanced. Studies in a continuous flow system showed the use of SC-CO2 affected the distribution of hydrocarbons, mainly producing heavier hydrocarbons (diesel fuel). In this thesis, results from four long term experiments (21-28 day) varying the CO2:syngas ratio are reported. The experiments were conducted at 350 oC, 1200 psi with a feed rate of 200sccm in a fixed bed supercritical reactor with a volume of 150 cc. The results show that the conversion of syngas increased from 47% to 95% at the optimum ratio 5:1 (CO2:Syngas). The steady state reaction rate constant also increased 4.756 times the baseline run from 0.021215 min-1 to 0.100907 min-1, for pure syngas and a CO2:syngas ratio of 5:1 respectively. The deactivation rate did not improve with the use of supercritical CO2; however, the life span of the catalyst more than doubled that of the base line run with an increase in SC- CO2. Product tailoring can also be performed by simply changing the SC-CO2:Syngas ratio. Ratios less than 5:1 will yield a product distribution of predominately alcohols, ratios greater than 5:1 produce heavier hydrocarbons. Both of these product distributions can be beneficial, but for this research a ratio of 5:1 yielded the desired product distribution of light to heavy hydrocarbons generically known as gasoline and diesel fuel. Liquid selectivity was observed to increase with CO2 content in the feed upto a CO2:syngas ratio of 5:1, thereafter it declined slightly. CO2 is produced in the experiment of pure syngas with no Sc-CO2, however the introduction of Sc-CO2 resulted in the consumption of CO2 for the production of hydrocarbons. The methane selectivity was found to monotonically decrease with the increase in CO2 content in the feed. With oil prices increasing, the use of SC- CO2 as a reaction media for FTS is showing more promise in providing liquid fuels more effectively. The evidence of consumption of CO2 means that CO2 does not need to be removed from the syngas feed stream after the gasification and water gas shift unit processes. The increase in the observed life of the catalyst under supercritical conditions will ultimately reduce the operating cost as less material will be needed to produce the same amount of product allowing for FTS to become economically competitive.

Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-12-08Bitstream added on 2014-06-13T18:40:02Z : No. of bitstreams: 1 arceferrufino_gla_me_guara.pdf: 1056072 bytes, checksum: 1cac7a1cd9ce6c0468bceb4898770311 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O dióxido de carbono (CO2) é um importante gás de efeito estufa. No entanto, um aumento gradual ameaça substancialmente o clima. Um dos principais desafios do planejamento ambiental é identificar um modelo que vincule todos os fatores do ciclo de carbono, ou seja, oceano – ecossistema terrestre – emissão antropogênica – atmosfera. Princípios básicos de Termodinâmica podem ser aplicados em uma modelagem estatística com bases em séries históricas para obter concentrações de CO2 na atmosfera, possibilitando a construção de cenários para uma melhor tomada de decisões. Por este motivo, foi desenvolvido no trabalho um modelo que interliga todos os fatores do ciclo de carbono, focalizando em quatro zonas térmicas ou climáticas (Boreal, Temperada, Tropical, Polar), para cálculos de armazenamento de CO2 atmosférico. Os resultados mostram que no ano 2100 se atingirá uma concentração de CO2 quatro vezes maior do que antes do período pré-industrial. A zona temperada emite quase a metade de dióxido de carbono à atmosfera na atualidade; para o ano 2100, essa emissão aumentará a quinze vezes mais que a zona tropical. A China será responsável em uma proporção de vinte quatro a onze com relação aos Estados Unidos. A estabilização das concentrações de CO2 na atmosfera será obtida quando as emissões de dióxido de carbono antropogênico tiverem uma diminuição de mais do que trinta e quatro por cento para o ano 2100 na zona temperada. / Carbon dioxide (CO2) is the most important greenhouse gas. A gradual increase on its atmospheric concentration threatens significantly the climate. One of the main challenges of environment planning is to identify a model that connects all factors that determine the carbon cycle, that is, ocean – terrestrial ecosystem – anthropogenic emissions – atmosphere. Basic thermodynamic principles can be applied in a statistical modeling with historic time series to obtain atmospheric CO2 concentration, creating the possibility of construction of scenarios that will help decision making. A model that links all carbon cycle factors was developed in this dissertation work, focusing in four thermal of climatic zones (Boreal, Temperate, Tropical, and Polar) for calculations of atmospheric CO2 storage. Results show that in 2100, the atmospheric CO2 concentration will reach a value four times higher than that of the pre-industrial period. The temperate zone already emits almost half of the carbon dioxide to the atmosphere; by 2100, this emission will increase 15 times more than that corresponding to the tropical zone. China will be responsible for emissions in a proportion of 24 to 11 in comparison to that of the United States. Stabilization of CO2 concentrations in the atmosphere will be obtained when the anthropogenic carbon dioxide emissions attain a decrease of at least 34% in 2100 in the temperate zone.

Made available in DSpace on 2018-08-01T21:58:47Z (GMT). No. of bitstreams: 1 tese_10597_Dissertação Tamires FINAL 08042017.pdf: 3045708 bytes, checksum: 346790de110160baf3a5382b4013c028 (MD5) Previous issue date: 2017-02-20 / O petróleo ainda continua sendo a maior fonte de energia não renovável do planeta. No seu estado bruto tem pouca utilidade. No entanto, seus derivados apresentam alto valor econômico. Nas etapas de processamento primário do petróleo alguns compostos de ocorrência natural são indesejáveis, como os ácidos naftênicos, resinas, asfaltenos, compostos sulfurados e metálicos. O poder corrosivo dos ácidos naftênicos preocupa as indústrias petrolíferas devido ao prejuízo causado nas tubulações e refinarias. Estudos recentes indicam que uma parcela desses ácidos quando submetidos a elevadas temperaturas (>280°C) pode sofrer reações de descarboxilação e degradação térmica, originando dióxido de carbono (CO2) e ácidos de cadeias menores como produtos de degradação. Os ácidos de cadeias menores juntamente com os ácidos naftênicos que se mantiveram preservados são corrosivos e o CO2 ao entrar em contato com água forma o ácido carbônico (H2CO3), podendo contribuir nas taxas de corrosão nos equipamentos do refino. Assim, o presente trabalho consistiu no desenvolvimento de uma metodologia para quantificação online do CO2 liberado no processo de destilação de petróleo. A metodologia desenvolvida foi baseada na técnica de microcromatografia gasosa. Os dados quantitativos de concentração de CO2 gerados pela microcromatografia foram relacionados com os valores de temperaturas de destilação, obtendo-se assim uma variação na concentração de CO2 de acordo com a temperatura de destilação do óleo. Com os resultados obtidos observou-se que para todos os petróleos destilados houve uma tendência na formação do gás CO2 partir de temperaturas superiores a 200°C. Na tentativa de elucidar a possível origem deste gás, supôs um mecanismo de descarboxilação para tais ácidos

The work undertaken involved the exploration of CO2 electroreduction systems, focussing heavily upon electrocatalysis utilising an array of electrochemical, spectroelectrochemical and spectroscopic techniques. The identification and characterisation of a relatively inexpensive and simple electrocatalyst for CO2 reduction was achieved, with the optimisation and development undertaken in such a manner that not just the electrocatalytic species, but also the entire electrochemical system was investigated, in order to determine and better understand the roles played by the various components. The complex of interest, Mo(CO)4bpy, represents the first molybdenum based molecular electrocatalyst reported to be active toward CO2 reduction, despite the prominence of Mo in enzymes with analogous function. The electrochemical characterisation of the complex in the both the presence and absence of CO2 was undertaken, yielding valuable information on the redox behaviour of the complex within the non-aqueous system in which it was employed and highlighting previously unreported features such as a third reduction and new reoxidation attributed to the reoxidation of a tricarbonyl anionic species. Non-aqueous solvents were chosen as they provide greater CO2 solubility than water with portions of the investigation undertaken in tetrahydrofuran, THF, then moving to the less widely used N-methylpyrrolidone, NMP. NMP is significantly less volatile than THF and has a large negative electrochemical window so is ideal for looking at reduction processes and, importantly, is also used as a commercial CO2 scrubbing solvent. Upon addition of CO2 to the Mo(CO)4bpy system there was an observable lowering of the overpotential by over 300 mV, and significant increase in CO2 associated current when compared to that for ‘direct’ CO2 reduction within the same system, at the reduction potential associated with the first reduction of the tetracarbonyl bipyridyl species. The confirmation of the anionic radical as the active species was attained through DFT calculation and EPR spectroelectrochemistry. Under inert gas the spectrum rapidly generated upon application of the first reduction potential is consistent with the expected response for the radical anionic [Mo(CO)4bpy] •−. When the system is saturated with CO2 this radical is no longer detectable. This supports the idea that the unpaired electron is transferred from the [Mo(CO)4bpy]•− to the CO2 molecule and also suggests that this transfer is rapid as no adduct is detectable via EPR even at reduced temperature (240 K). This is in keeping with the rate constants calculated from the voltammetric measurements made. The stability and activity toward CO2 reduction exhibited by Mo(CO)4bpy displayed a strong dependence on working electrode material, with gold proving optimal, indicative of adsorption being significant in the process. Optimisation of both the catalyst structure and the solvent and electrolyte system were also explored, as well as the (somewhat less directly related) comparison of various sources of diffusivity data.

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A study has been made of the dissolution of naturally occurring α-iron oxide hydrate in acidified aqueous solutions of sulphur dioxide at 110°C. The dissolution was found to be independent of acidity at low concentrations of sulphur dioxide and inversely dependent on acidity at higher concentrations of sulphur dioxide. Both homogeneous and heterogeneous control of the reaction was observed. The addition of cupric ion to the system catalysed the rate. Dissolution is thought to occur via hydration of the oxide surface and subsequent reaction of undissociated sulphurous acid at the surface to form a ferric-sulphite complex. The rate determining step is considered to be the desorption of the complex from the surface. A limited study of the direct dissolution of iron oxide hydrate in sulphuric and perchloric acids at temperatures between 120 and 150°C is included. Under these conditions, the hydrated oxide surface is thought to undergo anion exchange during dissolution. Work carried out on the preparation and identification of the isomeric α- and γ-iron oxide hydrates is reported. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

[No abstract available] / Science, Faculty of / Chemistry, Department of / Graduate

Analysis of the sulfur dioxide long wavelength band, appearing in n-ROH or benzene and carbontetrachloride solutions, has been obtained in terms of the system:- donor + SO₂ ⇌ complex The characteristic constants for the MeOH , EtOH , n-PrOH, n-BuOH and benzene complexes and the heat of formation of the benzene and ethanol complexes with sulfur dioxide in carbontetrachloride have been estimated. Structures for the n-ROR – SO₂ complexes have been proposed along the lines of Mulliken's simple charge transfer theory. It has been shown that the spectroscopic behaviour of sulfur dioxide in mixed benzene - ethanol solutions is adequately explained in terms of the binary donor system:- benzene + SO₂ ⇌ (complex)₁ ethanol + SO₂ ⇌ (complex)₂ if it is assumed that the characteristic constants for both complexes and the molar extinction curve of free sulfur dioxide remains unchanged in passing from non - polar to polar solvents. From a similar analysis of the new band appearing in hydroquinone - sulfur dioxide - ethanol solutions, the characteristic constants and heat of formation of the hydroquinone - sulfur dioxide complex have been obtained. The value for the heat of formation of this complex is in good agreement with the reported value of the heat of decomposition of the hydroquinone - sulfur dioxide clathrate compound. This fact, together with the evidence of the binary donor character of the ethanol - benzene - sulfur dioxide system is strong evidence in favour of the proposed theory of the formation of liquid lattice penetration complexes (by penetration of the liquid lattice by sulfur dioxide). From studies of the temperature dependence of the long wavelength band in sulfur dioxide - water solutions, it has been concluded that neither Ley and Konig nor Boyd Campbell and Maass’ theories adequately describe the behaviour of the sulfur dioxide - water system. A new theory has been proposed which qualitively describes the behaviour of this system. However, attempts to obtain values for the constants involved from the absorption spectra of water-ethanol-sulfur dioxide solutions, have been unsuccessful. This has been attributed to the simultaneous formation of ethanol - water interpenetration complexes (water penetrating the ethanol lattice). / Science, Faculty of / Chemistry, Department of / Graduate