Countries around the world face social, economic, and ecological damage from escalating natural disasters caused by climate change. In an effort to curtail climate change impacts, local and regional governments are beginning to employ green house gas (GHG) mitigation strategies to reduce their carbon footprint. These strategies work to eliminate a range of GHG emissions from entering the atmosphere. Apart from carbon dioxide (CO₂), the most prevalent GHG is methane. In terms of global warming, methane is approximately 21 times more harmful to the atmosphere than CO₂. Natural gas systems, coal mining, manure management, rice cultivation, wastewater treatment, and landfills all contribute to methane generation. According to the US Environmental Protection Agency's 2011 US GHG inventory, landfills generate 1.5% of total GHG emissions in carbon dioxide equivalents. Recognizing the global impacts of its policies and operations, municipalities are working to reduce their GHG emissions. Coalitions like the C40 Cities Climate Leadership Group were created to specifically address GHG reductions, which will result in a 248 million MT reduction in GHGs released to the atmosphere by 2020. Guided by existing literature, this Master's Report calculates methane generation and transport to determine the effectiveness of applying two methane mitigation alternatives--passive methane oxidation biocovers (PMOBs) and landfill gas to energy technologies (LFGTE)--at an inactive landfill site to reduce GHG emissions. LFGTE generates energy for direct use such as space heating or industrial processes or for electricity generation. Cost-saving strategies abound for landfills which utilize LFGTE. PMOBs optimize the landfill surface soil cover environment to promote microbial growth of bacteria, called methanotrophs, which convert methane into carbon dioxide. When employed, these mitigation alternatives are designed to significantly reduce methane emissions from landfills. The EPA has developed a computer modeling program (LANDGEM) to aid in the calculation of landfill gas generation. A hypothetical case study of a one million ton landfill was created and modeled for methane generation over a 35 year period. With methane generation rates calculated, assessment of potential LFGTE was performed and methane oxidation rate calculations were made to determine the impact of a PMOB and LFGTE on net GHG emissions at the landfill. The overall GHG reductions with these engineering controls were two-thirds of the level a landfill without controls would emit. These results indicate that implementing methane mitigation steps at closed landfills throughout the world would yield significant reductions in GHG emissions. / text

Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains x, 118 p. : ill. Includes abstract. Includes bibliographical references.

Lakes play a major role in the global carbon (C) cycle, despite making up a small area of earth’s surface. Lakes receive, transport and process sizable amounts of C, emitting a substantial amount of the greenhouse gases, carbon dioxide (CO2) and methane (CH4), into the atmosphere. Ice-covered lakes are particularly sensitive to climate change, as future reductions to the duration of lake ice cover will have profound effects on the biogeochemical cycling of C in lakes. It is still largely unknown how reduced ice cover duration will affect CO2 and CH4 emissions from ice-covered lakes. Thus, the primary aim of this thesis was to fill this knowledge gap by monitoring the spatial and temporal dynamics of CO2 and CH4 in ice-covered lakes. The results of this thesis demonstrate that below ice CO2 and CH4 were spatially and temporally variable. Nutrients were strongly linked to below ice CO2 and CH4 oxidation variations across lakes. In addition, below ice CO2 was generally highest in small shallow lakes, and in bottom waters. Whilst below ice CH4 was elevated in surface waters near where bubbles from anoxic lake sediment were trapped. During the ice-cover period, CO2 accumulation below ice was not linear, and at ice-melt incomplete mixing of lake waters resulted in a continued CO2 storage in bottom waters. Further, CO2 transported from the catchment and bottom waters contributed to high CO2 emissions. The collective findings of this thesis indicate that CO2 and CH4 emissions from ice-covered lakes will likely increase in the future. The strong relationship between nutrients and C processes below ice, imply that future changes to nutrient fluxes within lakes will influence the biogeochemical cycling of C in lakes. Since catchment and lake sediment C fluxes play a considerable role in below ice CO2 and CH4 dynamics, changes to hydrology and thermal stability of lakes will undoubtedly alter CO2 and CH4 emissions. Nevertheless, ice-covered lakes constitute a significant component of the global C cycle, and as such, should be carefully monitored and accounted for when addressing the impacts of global climate change.

Résumé : Les biosystèmes d’oxydation passive du CH[indice inférieur 4] constituent une alternative techniquement et économiquement viable pour la réduction des émissions fugitives de CH[indice inférieur 4] dans l’atmosphère par les sites d’enfouissement. Directement intégrés au recouvrement final, ils sont constitués d’une succession de couche de matériaux au sein desquelles se développent les bactéries méthanotrophes capable d’oxyder le CH[indice inférieur 4] en CO[indice inférieur 2] de façon passive, en présence de l’oxygène moléculaire. La capacité des BOPMs à réduire les émissions de CH[indice inférieur 4] a été associée à plusieurs paramètres météorologiques et environnementaux, entre autres la végétation. L’objectif de ce projet est de déterminer l’effet de la végétation dans l’oxydation du CH[indice inférieur 4] par les biosystèmes. Pour atteindre cet objectif, des études de l’efficacité d’oxydation du CH[indice inférieur 4] dans des bacs pourvus de végétation, dans des conditions contrôlées de laboratoire et partiellement contrôlées de terrain, suivie d’une étude de la cinétique d’oxydation des sols de rhizosphère pré-conditionnés au CH[indice inférieur 4], ont été effectuées. Quatre bacs ont été testés, comprenant : le trèfle blanc (Trifolium repens L.), la fléole des prés (Phleum pratense L.), un mélange des deux espèces végétales (mélange) et le sol nu (dépourvu de végétation). Les résultats des bacs d’oxydation ont montré que, jusqu’à un débit de 100 g CH[indice inférieur 4]/m[indice supérieur 2]/jr, les espèces végétales n’avaient pas d’influence sur les résultats, et les efficacités d’oxydation étaient de l’ordre de ~100%. Au-delà de cette valeur, les efficacités étaient toujours élevées, et une différence statistiquement significative a été observée entre les espèces végétales. Le sol nu était le plus efficace, tandis que le mélange et le trèfle étaient les moins efficaces au laboratoire et sur le terrain respectivement. Néanmoins, les différences d’efficacités entre les bacs n’étaient pas très grandes et les taux d’oxydation dans les bacs n’ont pas cessé de croitre tout au long des essais, suggérant que la capacité d’oxydation maximale des bacs n’a pas été atteinte. L’étude de la cinétique d’oxydation a également montré que la végétation n’avait pas d’effet significatif sur les taux d’oxydation. Ces observations ne corroborent pas ce qui est rapporté dans la littérature concernant l’effet positif de la végétation. Néanmoins, les conclusions de cette étude ont été en adéquation par l’analyse des profils d’efficacité, de la biomasse racinaire et des caractéristiques physico-chimiques des sols du BOPM. Par ailleurs, un effet significatif de la végétation sur le degré de saturation en eau dans les BOPMs a également été observé. Cette dernière observation a été associée au mécanisme de régulation de la teneur en eau par les racines des plantes. Les principales limitations de cette étude concernaient la durée des essais et le nombre d’espèces végétales. En résumé, pour les espèces végétales testées, il a été démontré que la végétation ne constitue pas un facteur clé stimulant l’oxydation du CH[indice inférieur 4] dans les BOPMs. De plus, l’étude de la cinétique d’oxydation a montré que de meilleur taux d’oxydation étaient obtenus dans un sol de rhizosphère modérément pré-exposé au CH[indice inférieur 4] comparativement à un sol sans végétation, ou à une rhizosphère non pré-exposée ou très pré-exposée au CH[indice inférieur 4]. / Abstract : The passive CH[subscript 4] oxidation Biosystems are a cost-effective technology for the reduction of landfills fugitive CH[subscript 4] emissions in the atmosphere. As part of the final cover, they are made up of a sequence of soil layers capable to develop methanotrophic bacteria for passive CH[subscript 4] oxidation into CO[subscript 2], in the presence of molecular oxygen. The ability of biosystems to reduce CH[subscript 4] emissions was related to several meteorological and environmental parameters, including vegetation. The main objective of this project is to determine the effect of vegetation on CH[subscript 4] oxidation by biosystems. Studies of the CH[subscript 4] oxidation efficiencies of vegetated column under controlled conditions prevailing in the laboratory and under the partially controlled conditions in the field, followed by the study of the CH[subscript 4] oxidation kinetics of the preconditioned rhizospheric soil, were carried out. Four columns were tested, including: white clover (Trifolium repens L.), timothy grass (Phleum pratense L.), a mixture of both (mixture) and bare soil (control biosystem). The results of the column study showed that up to a loading of 100 g CH[subscript 4]/m[superscript 2]/d, plant species did not influence the results, and the CH[subscript 4] oxidation efficiencies were in the vicinity of ~ 100%. Beyond this value, the efficiencies were still high, and a statistically significant difference was observed between plant species. Bare soil was the most efficient while the mixture and white clover were the least in the laboratory and the field respectively. However, differences in efficiencies between the columns were not high and the oxidation rates continued to increase throughout the test, suggesting that the maximum oxidation capacity of the biosystems tested may have never been fully attained. The kinetics study also showed that vegetation did not have significant effect on CH[subscript 4] oxidation rate. These observations do not corroborate what is reported in technical literature on the positive effect of vegetation. Nevertheless, the findings of this study were adequacy with the analysis of the profiles of efficiencies, root biomass and physico-chemical characteristics of soils. Moreover, a significant effect of vegetation on the degree of water saturation in Biosystems was also observed. The latter was associated with the mechanism of water content regulation through plant roots. The main limitations of this study concerned the duration of the tests and the number of plant species. In summary, for the plant species studied herein, it was shown that the vegetation is not a key factor for enhancing CH[subscript 4] oxidation in biosystems. Moreover, the study of the kinetics of CH[subscript 4] oxidation showed that better oxidation rate were obtained in a moderately pre-exposed rhizospheric soil compared to bare soils, to never before pre-exposed or very pre-exposed rhizospheric soils to CH[subscript 4].

At present, more than 80% of the world’s energy consumption and production of chemicals is originated from the use of fossil resources. There is a tremendous growing interest in utilising biomass molecules for energy provision due to their carbon neutrality. Lower alcohols such as methanol and ethanol if produced from biomass as transportation fuels as well as platform chemicals, can become strategically important for many energy/chemically starved countries. Currently, they are synthesised by indirect and inefficient processes. We show for the first time in this thesis study that ethylene glycol, the simplest representative of biomass-derived polyols, can be directly converted to these two lower alcohols by selective hydrogenolysis over modified Raney Ni and Cu catalysts in hydrogen atmosphere. This work provides essential information that may lead to the development of new catalysts for carbohydrate activation to methanol, a novel but important reaction concerning the important biomass conversion to transportable form of energy. Modification of electronic structure and the adsorption properties of Raney catalysts have therefore been achieved by blending with second metal(s). It is found that the activity and selectivity of this reaction can be significantly affected by this approach. In contrast, there is no subtle effect on methanol selectivity despite a great variation in the d-band centre positions of metal catalysts which show a distinctive effect on other products. Our result suggests that methanol is produced on specific surface sites independent from the other sites at an intrinsic rate and will not be converted to other products by the d-band alteration. On the other hand, it is reported in this thesis that a dramatic improvement in the combined selectivity to methanol/ethanol reaching 80% can be obtained over a Pd/Fe₃O₄ catalyst under relatively milder conditions (20 bar and 195 oC). This direct production of the non-enzymatic bio-alcohols is established over a carefully prepared co-precipitated Pd/Fe₃O₄ catalyst which gives a metallic phase of unexpectedly high dispersion ranging from small clusters to individual metal adatoms on defective iron oxide to give the required metal-support interaction for the novel synthesis. It is demonstrated that the small PdFe clusters on iron oxide surface provide the active species responsible for methanol production. In addition, a related Rh/Fe₃O₄ catalyst synthesised by co-precipitation is also shown to be selective for CO₂ and H₂ production from a direct methane-oxygen oxidation reaction. As a result, 2.7% conversion of methane with selectivity ratio of CO₂/H₂ = 4 in a mixed gas feed stream of CH₂/O₂ = 30 at 300 ^oC is obtained. The reaction is operated in a kinetically controlled regime at 300^oC, where the CO formation from reverse water gas shift reaction is greatly suppressed. It is evident that the Rh/Fe₃O₄ acts as an interesting bifunctional catalyst for this reaction. This catalyst firstly gives a high dispersion of Rh which is expected to deliver a higher surface energy with enhanced activity. The Rh metal surface provides catalytically active sites for dissociation of methane to adsorbed hydrogen and carbon atoms effectively, and active oxygen on metal surface readily catalyses the carbon atoms to CO. Following these elementary reactions, the surface oxygen from Fe₃O₄ subsequently converts it to CO₂ selectively at the metal-support interface. As a result, the novel study of catalytic biomass conversion and the discoveries of new catalysts are reported in this thesis.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2007. / The catalytic selective oxidation of hydrocarbon molecules is the process where a selectively oxidized intermediate molecule is formed instead of the thermodynamically favoured total oxidation products, in the presence of a suitable catalyst. Examples are the selective oxidation of methane to synthesis gas at moderate temperatures, for which a catalyst is still needed and the selective oxidation of propene to acrolein over α-Bi2Mo3O12. The selective oxidation of propene over α-Bi2Mo3O12 occurs via a Mars-van Krevelen mechanism where the bulk oxygen in the catalyst is inserted into the propene molecule and leaves as part of the product, while being replaced with gaseous oxygen. From an economic perspective there is a need to produce synthesis gas from methane at low temperatures. It was seen in the literature that α-Bi2Mo3O12 is a mixed metal oxide that might be capable of achieving this. The feasibility of the selective oxidation of methane to synthesis gas with α-Bi2Mo3O12 was therefore investigated. However, it was found that the selective oxidation of methane over α-Bi2Mo3O12 is not feasible at moderate temperatures. To circumvent the problem of producing synthesis gas at low temperatures a membrane reactor was suggested that might be able to produce synthesis gas at moderate temperatures with conventional selective methane oxidation catalysts that thermodynamically favours carbon dioxide formation at low temperatures. No time on-stream experiments had been done previously for the selective oxidation of ...

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / Extensive research has gone into developing and modeling the three-way catalyst (TWC) to reduce the emissions of hydrocarbons, NOx and CO from gasoline-fueled engines level. However, much less has been done to model the use of the three-way catalyst to treat exhaust from natural gas-fueled engines. Our research address this gap in the literature by developing a detailed surface reaction mechanism for platinum based on elementary-step reactions. A reaction mechanism consisting of 24 species and 115 elementary reactions was constructed from literature values. All reaction parameters were used as found in the literature sources except for steps modified to improve the model fit to the experimental data. The TWC was simulated as a one-dimension, isothermal plug flow reactor (PFR) for the steady state condition and a continuous stirred-tank reactor (CSTR) for the dithering condition. This work describes a method to quantitatively simulate the natural gas engine TWC converter performance, providing a deep understanding of the surface chemistry in the converter. Due to the depletion of petroleum oil and recent volatility in price, synthesizing value-added chemicals from biomass-derived materials has attracted extensive attention. 1, 3-butadiene (BD), an important intermediate to produce rubber, is conventionally produced from petroleum. Recently, one potential route is to produce BD by dehydration of 2, 3-butanediol (BDO), which is produced at high yield from biomass. This reaction was studied over two commercial forms of alumina. Our results indicate acid/base properties greatly impact the BD selectivity. Trimethylamine can also modify the acid/base properties on alumina surface and affect the BD selectivity. Scandium oxide, acidic oxide or zirconia dual bed systems are also studied and our results show that acidic oxide used as the second bed catalyst can promote the formation of BD, while 2,5-dimethylphenol is found when the zirconia is used as the second bed catalyst which is due to the strong basic sites.

O principal objetivo deste trabalho foi a avaliação de estratégias que viabilizassem o uso do metano como doador de elétrons para desnitrificação em ambiente anóxico, visando à aplicação de tecnologia para pós-tratamento de efluente de reatores de manta de lodo e fluxo ascendente (UASB) aplicado no tratamento de esgoto sanitário. O trabalho foi dividido em cinco etapas, sendo que em todas elas o metano foi fornecido como única fonte de carbono orgânico. Na Etapa 1, foram comparados dois inóculos, em reatores em batelada sequenciais (SBR) com biomassa imobilizada. Como inóculo, foi utilizada mistura de sedimento marinho e sedimento de mangue (SED-SBR) ou lodo de reator UASB (LAn-SBR). Na Etapa 2, foram avaliadas estratégias de enriquecimento da comunidade metanotrófica desnitrificante. Para tanto, foram operados dois SBRs: um com biomassa imobilizada (Imob-SBR) e outro com biomassa suspensa (Susp-SBR). Na Etapa 3, foi operado reator contínuo de leito fixo e estruturado e fluxo ascendente (Up-FSBR). Nas etapas 1 e 3, o metano suportou a ocorrência da desnitrificação e da manutenção celular. O consumo das formas nitrogenadas na Etapa 2 foi muito baixo e não foi possível concluir qual a melhor estratégia para enriquecimento da biomassa. Na Etapa 4, a biomassa retirada do Up-FSBR ao final da operação foi submetida a testes de endogenia. Foram operadas bateladas simples e, em cada uma, foi dosada apenas uma das formas nitrogenadas em condições com metano e sem metano. Os resultados mostraram que a redução das formas nitrogenadas é um processo paralelo à oxidação de metano. Na Etapa 5, foi avaliado o consumo de metano e de nitrato em SBR com biomassa suspensa em condições microaeradas e anóxicas. Foi observado que tanto a oxidação do metano quanto a redução do nitrato ocorrem em maior intensidade quando expostos a condições de microaerofilia. A análise dos resultados obtidos permite concluir que os organismos responsáveis pela redução de nitrato (MD) estabeleceram uma relação sintrófica com as bactérias oxidadoras de metano (MM). Observou-se que, quando as bactérias oxidadoras de metano foram estimuladas, a desnitrificação ocorreu em maior intensidade. / This work aimed to develop the methane (CH4) application as electron donor to denitrification under anoxic conditions for post-treatment of Upflow Anaerobic Sludge Blanket (UASB) effluent, applied in sewage treatment systems. The study was conducted in five stages, in which methane was provided as the sole organic carbon source. In Stage 1, methanotrophic denitrification was assessed in Sequencing Batch Reactors (SBR) inoculated with a blend of marine and mangrove sediments (SED-SBR) or anaerobic sludge (LAn-SBR). For both inocula. In Stage 2, strategies for the enrichment of methanotrophic-denitrifying community were evaluated. Two SBRs were operated: in one of them, biomass was immobilized (Imob-SBR) while the other was inoculated with suspended biomass (Susp-SBR). In Stage 3, methanotrophic denitrification was addressed in an Upflow Fixed-Structured Bed Reactor (Up-FSBR). In Stages 1 and 3, methane supported denitrification and cellular maintenance. In Stage 2, the consumption of oxidized nitrogen compounds was too low, and it was not possible to conclude which is the better strategy for enrichment of the methanotrophic-denitrifying community. In Stage 4, the biomass withdrawn from Up-FSBR was subjected to endogeny tests, in batch reactors. In each batch reactor, only nitrite or nitrate was provided, and both methane and methane-free conditions were tested. It was observed that nitrite and nitrate reduction occurred as a marginal process. In Stage 5, methane oxidation coupled to denitrification was assessed under both anoxic and microoxic conditions and both processes were stimulated under the latter. The obtained data suggest denitrifiers established a syntrophic relationship with methane-oxidizers, and when the latter was stimulated, the denitrification also occurred in greater extent.

The catalytic combustion of methane in excess of O2 over Pd catalysts was studied on model catalysts, including polycrystalline palladium foil and palladium single crystals. The kinetics of this reaction could be measured at conditions not accessible to supported catalysts and, thus, the issues of structure sensitivity, mechanism, hysteresis on oxidation, and deactivation could be studied in detail. Methane oxidation on PdO was insensitive to the original metal surface structure which PdO grew from, with turnover rates in the range of 1.3-4.7 s-1 on (111), (100) and (110) single crystals at 160 Torr O2, 16 Torr CH-4, 1 Torr H2O and 598 K. Methane oxidation on Pd metal was also insensitive to the original surface structure, with the turnover rate in the range of 2.0-2.8 s-1 on the three single crystals at 2.3 Torr O2, 0.46 Torr CH4, 0.05 Torr H2O and 973 K. Since there is no support effect and the surface purity could be certified, these turnover rates for this reaction can be used as a benchmark. The turnover rate for methane oxidation was found to decrease 95% when PdO decomposed to Pd metal at 888 K, showing that PdO was more active than Pd metal for methane combustion at this temperature. Water inhibition to the reaction was not observed at a temperature above 813 K on both PdO and Pd metal, while it was observed at 598 K on PdO. The activation energy on PdO was 32 kJ mol-1 in the range of 783-873 K, while it was 125 kJ mol-1 in the range of 568-623 K. The activation energy on Pd metal was 125 kJ mol-1 in the range of 930-980 K. The change of reaction orders and activation energies suggests that the reaction mechanism is a function of temperature and palladium chemical states. We propose that adsorbed water, the most abundant surface intermediate at 598 K, was not present in significant quantities at temperatures above 783 K. This change in surface inhibition by water is the reason for lower activation energy at temperatures above 783 K. Interaction between the catalyst and support, or presence of impurities, is one of the factors for catalyst deactivation. The interaction between oxidized silicon and palladium was investigated on a polycrystalline palladium foil and on supported Pd/SiO2 catalysts. During methane oxidation, oxidized silicon covered the palladium oxide surface as observed by TEM on Pd/SiO2 catalysts and by XPS on palladium foil. On Pd foil, the source of silica was a silicon impurity, common on bulk metal samples. The migration of oxidized silicon onto PdO deactivated the catalysts by blocking the active sites for methane oxidation. Silicon oxide overlayers were also observed covering the Pd surface after reduction of Pd/SiO2 by H2 at 923 K.

Due to continuously stricter regulations regarding emissions from power generation processes, further development of existing gas turbine combustors is essential. A promising alternative to conventional flame combustion in gas turbines is catalytic combustion, which can result in ultralow emission levels of NOx, CO and unburned hydrocarbons. The work presented in this thesis concerns the development of methane oxidation catalysts for gas turbine combustors. The application of catalytic combustion to different combustor concepts is addressed in particular. The first part of the thesis (Paper I) reports on catalyst development for fuel-lean methane combustion. Supported Pd-based catalysts were investigated at atmospheric pressure. The effect on catalytic activity of diluting the reaction mixture with water and/or carbon dioxide was studied in order to simulate a combustion process with exhaust gas recirculation. The catalytic activity was found to decrease significantly in the presence of water and CO2. However, modifying the catalyst by changing support material can have a considerable impact on the performance. In the second part of this thesis (Papers II-IV), the development of rhodium catalysts for fuel-rich methane combustion is addressed. The effect of catalyst composition, oxygen-to-fuel ratio and catalyst pre-treatment on the methane conversion and the product gas composition was studied. An experimental investigation at elevated pressures of partial oxidation of methane/oxygen mixtures in exhaust gas-rich environments was also conducted. The most suitable catalyst identified for fuel-rich catalytic combustion of methane, i.e. Rh/Ce-ZrO2, showed benefits such as low light-off temperature, high activity and enhanced hydrogen selectivity. In the final part of the thesis (Paper V), a numerical investigation of fuel-rich catalytic combustion is presented. Measurements and predictions were compared for partial oxidation of methane in exhaust gas diluted mixtures at elevated pressures. The numerical model was validated for several Rh-based catalysts. The key parameter controlling the catalytic performance was found to be the noble metal dispersion. / QC 20110125