Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-02Bitstream added on 2014-06-13T19:39:27Z : No. of bitstreams: 1 souza_acc_me_guara.pdf: 1178727 bytes, checksum: 36f6a2063176d1106a7c533e016baa05 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Universidade Estadual Paulista (UNESP) / Neste trabalho efetua-se análises técnica e econômica de um reformador a vapor de etanol para a produção de 0,7 Nm3/h de hidrogênio, capacidade esta suficiente para acionar uma célula de combustível do tipo PEMFC de 1 kW. A análise técnica abrange análises físico-química e termodinâmica (que envolve inclusive análise exergética), que consiste em fornecer as faixas de temperatura e pressão necessárias à reforma a vapor, e na determinação dos volumes de reagentes consumidos (neste caso, etanol e água). Foi possível obter informações sobre os principais produtos da reforma a vapor (hidrogênio e dióxido de carbono) e o grau de avanço da reação de reforma do etanol. As informações necessárias para o início da modelagem foram obtidas da literatura. A análise exergética permitiu avaliar as melhores condições (temperatura e pressão) para a reforma, baseando-se nos níveis de irreversibilidades. Finalmente, através da análise econômica, avaliou-se os custos de produção de hidrogênio em função do custo de investimento, operação e manutenção no reformador e acessórios. Foram selecionadas quatro fontes de calor para o processo (gás natural, gás liquefeito de petróleo, álcool e eletricidade). Conclui-se que a reforma a vapor de etanol é tecnicamente viável, podendo colocar o hidrogênio combustível no rol dos insumos energéticos alternativos e renováveis. Do ponto de vista econômico, o kWh de hidrogênio produzido por reforma de etanol apresenta o menor valor (numa faixa de 0,06471 a 0,10863 US$/kWh), devido ao alto custo de investimento e ao pequeno volume de produção de reformadores de etanol. Estes custos energéticos do hidrogênio poderão ser mais baixos, desde que haja uma maior produção em escala de reformadores de etanol. / In this work the technical and economic analysis of a steam reformer of ethanol is made. The objective is the production of 0.7 Nm3/h of hydrogen to be used in a 1 kW powered PEMFC. The technical analysis consists in physical and chemical, and thermodynamic studies (including the exergetic analysis). These analysis provide informations as temperature and pressure ranges for steam reforming and the volume of the used reactants (in this case, ethanol and water). Through a mathematic modeling, it s possible to get informations as the products of reforming (the hydrogen and carbon dioxide are the principal products) and the advance degree of the reaction. The useful informations for the modeling were got in the literature. Also about the technical analysis, an exergetic analysis was carried out, permitting obtain the best conditions (temperature and pressure) for the reforming based in the lowest irreversibilities level for the process. Finally, through the economic analysis, the costs of hydrogen production as a function of investment, operation and maintenance costs was made. Four heat sources for the process (natural gas, liquefied petroleum gas, ethanol and electricity) were considered for this analysis. This study has indicated that the steam reforming of ethanol is technically feasible, for the production of hydrogen as one of the alternative and renewable fuel. Economically, the hydrogen produced by steam reforming of ethanol presents the lowest cost, but expensive (at a range from 0,06471 to 0,10863 US$/kWh) because the high cost of investment and the small production of ethanol reformer.

Due to the environmental problems caused by the steadily increasing usage of fossil fuels, the interest for renewable sources of energy has amplified significantly. Among the several possibilities, hydrogen gas is considered to be one of the most promising fuels forof the future. IfOnce formed from water via photocatalysis it is a desirable, convenient and green improvement in the field of energy. During this work, we have tried to contribute to this important field. 4wt.% Au/TiO2 synthesized by deposition-precipitation with urea was the main photocatalysts used in this project. Other noble metal-loaded (Pt and Ag) titanium dioxide materials were synthesized by deposition precipitation with urea and other methods such as sol gel and sol immobilization. These catalytic systems were studied and their activity compared for hydrogen production from water/methanol mixtures. Sets of monometallic Au, Ag, Pt and bimetallic Au-Pt and Au-Ag supported titanium dioxide were synthesized and tested. Au/TiO2 photocatalysts synthesized by deposition precipitation with urea was were the best in terms of hydrogen production compared to other photocatalysts. In the evaluation of possible sacrificial molecules, isopropanol was less efficient than methanol. Through the formation of bi-metallic Ag-Au/TiO2 and Pt-Au/TiO2 catalysts, the hydrogen production could be further improved. Finally, Ir supported Al2O3 was investigated for the first time as a heterogeneous catalyst for hydrogen production by photocatalytic dehydrogenation of aqueous p-formaldehyde and photoreduction of carbon dioxide.

The energy consumptions worldwide have increased simultaneously with the growth of the population and of the economy. Nowadays, finding an alternative way to satisfy the energy demand is one of the great challenges for the future of humanity, especially due to the limitation of fossil fuels and their effect on global warming. Hydrogen, as an alternative fuel for the future, is very attractive. Compared to traditional methods, such as the steam reforming of natural gas or coal gasification, photocatalytic water splitting (PWS) is considered to be the most sustainable alternative for producing hydrogen as a future fuel. PWS usually relies on semiconductor material that can transform the absorbed solar photon into photogenerated electrons and holes, creating a photopotential which can drive the electrochemical production of molecular hydrogen from the reduction of water. Despite its promising application, semiconductor-based PWS usually suffers from low carrier mobility and short diffusion length. Furthermore, the recombination of photogenerated electrons and holes might occur, especially if there are no suitable reaction sites available on the surface of the semiconductor. In order to facilitate the catalytic reactions on the surface of the semiconductor, the presence of a cocatalyst is necessary in order to obtain more efficient PWS processes. To this day, noble metals such as Pt, Pd, RuO2 and IrO2 are still the benchmark cocatalysts for PWS. Nevertheless, due to their high cost and limited supply, it is mandatory to develop a suitable strategy and to identify more efficient materials. Therefore, within the framework of this dissertation, novel cocatalysts and strategies that can improve the efficiency of the photocatalytic water splitting processes have been developed. Firstly, we developed a cocatalyst combining noble metals and semiconductors by means of partial galvanic replacement of the Cu2O nanocrystal with Au. The deposition of this cocatalyst on TiO2 was studied for the photocatalytic H2 production in order to explore the synergistic effect of the plasmonic resonance from the Au nanoparticles and pn-junction between Cu2O and TiO2. Additionally, the plasmonic effect of the Au films was also studied and utilized in order to improve the PWS. Secondly, the nanoscaling of cocatalysts was studied in order to improve the efficiency thereof and to reduce the cost of the cocatalyst materials. Moreover, it is sought to explore the quantum size effect on the properties of the cocatalyst and their effect on the photocatalytic reaction. Atomically precise Au and Ni nanoclusters were employed in these studies. Au nanoclusters were studied in relation to the cocatalysts in the photocatalytic water splitting, and Ni nanoclusters were studied in relation to the cocatalysts in the electrocatalytic water oxidation. The results of these studies will provide new insights in relation to the strategy used in order to develop efficient cocatalysts for the purpose of photocatalytic water splitting.

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No / Methane reforming in the presence of hydrogen sulfide (H2SMR) is not only conspicuous in terms of producing valuable material but also because of its advantages in obtaining hydrogen as a clean fuel. Substitution of traditional hydrogen production processes such as methane steam reforming (MSR), elimination of natural gas amine–based H2S removal, and sulfur recovery processes have attracted much attention. The current hydrogen production is associated with consuming energy that is usually supplied by burning fossil fuels. Thus, producing hydrogen by current high greenhouse gas emitter methods seems not to be a rational approach to benefit from this clean energy source. Additionally, H2SMR with the potential of producing four moles of hydrogen and one mole of CS2 from methane could be a promising alternative as providing the opportunity to benefit from producing cleaner fuels and simultaneously making CS2 that is used for the production of more valuable products. This chapter reviews the recent progress in CS2 production from methane reforming in the presence of H2S and brings the effect of dominant parameters on this process.

There is a global need for sustainable, renewable and clean energy sources. Microbial production of hydrogen from renewable carbon sources, biorefinery compounds such as succinic acid or from food and drinks industry waste meets all these criteria. Although it has been studied for several decades, there is still no large scale bio-hydrogen production because the rate and yield of hydrogen production are not high enough to render the process economical. The dependency of biological hydrogen production of incipient light energy is also an important factor affecting economics. In order to improve the prospects of biohydrogen as a renewable and sustainable energy alternative, the genetic and process engineering approaches should be helped and targeted by metabolic engineering tools such as metabolic flux balance analysis. The overall aim of this research was the development of computational metabolic flux balance analysis for the study of growth and hydrogen production in Rhodobacter sphaeroides. The research reported in this thesis had two approaches; experimental and computational. Batch culture experiments for growth and hydrogen production by Rhodobacter sphaeroides were performed with either malate or succinate as carbon source and with glutamate as the nitrogen source. Other conditions investigated included; i) aerobic and anaerobic growth, ii) light and dark fermentation for growth, and iii) continuous light and cycled light/dark conditions for hydrogen production. The best growth was obtained with succinate under anaerobic photoheterotrophic conditions with the maximum specific growth rate of 0.0467 h– 1, which was accompanied with the maximum specific hydrogen production rate of 1.249 mmol(gDW.h)– 1. The range of the photon flux used was 5.457 - 0.080 mmol(gDW.h)– 1. The metabolic flux balance model involved 218 reactions and 176 metabolites. As expected the optimised specific rates of growth and hydrogen production were higher than those of the experimental values. The best prediction was for hydrogen production on succinate with computed specific hydrogen production rates in the range of 2.314 - 1.322 mmol(gDW.h)– 1. Sensitivity analyses indicated that the specific growth rate was affected by the nitrogen source uptake rate under aerobic dark condition whereas the flux of protein formation had the largest effect on the specific growth rate under anaerobic light condition.

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This work describes the application of porous metal supported Pd-membranes to the water-gas shift catalytic membrane reactor in the context of its potential application to the Integrated Gasification Combined Cycle (IGCC) process. The objective of this work was to develop a better understanding of Pd-membrane fabrication techniques, water-gas shift catalytic membrane reactor operation, and long-term behavior of the Pd-membranes under water-gas shift conditions. Thin (1.5 - 16 um) Pd-membranes were prepared by electroless deposition techniques on porous metal supports by previously developed methods. Pd-membranes were installed into stainless steel modules and utilized for mixed gas separation (H2/inert, H2/H2O, dry syngas, and wet syngas) at 350 - 450C and 14.5 atma to investigate boundary layer mass transfer resistance and surface inhibition. Pd-membranes were also installed into stainless steel modules with iron-chrome oxide catalyst and tested under water-gas shift conditions to investigate membrane reactor operation in the high pressure (5.0 - 14.6 atma) and high temperature (300 - 500C) regime. After the establishment of appropriate operating conditions, long-term testing was conducted to determine the membrane stability through He leak growth analysis and characterization by SEM and XRD. Pd and Pd/Au-alloy membranes were also investigated for their tolerance to 1 - 20 ppmv of H2S in syngas over extended periods at 400C and 14.0 atma. Water-gas shift catalytic membrane reactor operating parameters were investigated with a focus on high pressure conditions such that high H2 recovery was possible without a sweep gas. With regard to the feed composition, it was desirable to operate at a low H2O/CO ratio for higher H2 recovery, but restrained by the potential for coke formation on the membrane surface, which occurred at a H2O/CO ratio lower than 2.6 at 400C. The application of the Pd-membranes resulted in high CO conversion and H2 recovery for the high temperature (400 - 500C) water-gas shift reaction which then enabled high throughput. Operating at high temperature also resulted in higher membrane permeance and less Pd-surface inhibition by CO and H2O. The water-gas shift catalytic membrane reactor was capable of stable CO conversion and H2 recovery (96% and 88% respectively) at 400C over 900 hours of reaction testing, and 2,500 hours of overall testing of the Pd-membrane. When 2 ppmv H2S was introduced into the membrane reactor, a stable CO conversion of 96% and H2 recovery of 78% were observed over 230 hours. Furthermore, a Pd90Au10-membrane was effective for mixed gas separation with up to 20 ppmv H2S present, achieving a stable H2 flux of 7.8 m3/m2-h with a moderate H2 recovery of 44%. The long-term stability under high pressure reaction conditions represents a breakthrough in Pd-membrane utilization.