Dissertations / Theses on the topic 'Methane. Carbon dioxide. Hydrates'

Fourier transform infrared (FTIR) spectroscopy is commonly used in solution crystallization studies to monitor the crystal formation process. This analysis reflects the molecular vibrations within the solution. A crystallization process that is currently a very popular area of study is hydrate formation due to the possible application of gas hydrate research in the energy sector. A study of molecular vibrations was performed on two types of structure I gas hydrate, methane and carbon dioxide. Experiments were performed with a specialized high pressure sample cell placed inside an FTIR spectrometer. The experimentation was carried out at 253.15 K for both the methane and carbon dioxide systems and a pressure range of 2100 to 6800 kPa for the methane system and 1400 to 1700 kPa for the carbon dioxide system. This line of experimentation was able to assist in mapping the IR behavior of the hydrates studied and establish the presence of hydrate within a sample.

Thesis (M.S.)--West Virginia University, 2009.
Title from document title page. Document formatted into pages; contains x, 114 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2009.
Title from document title page. Document formatted into pages; contains viii, 93 p. : ill. (some col.), col. map. Includes abstract. Includes bibliographical references.

Petrobrás
Hidratos são estruturas cristalinas constituídas por moléculas de água e gás ou líquido, sendo que a estabilização dessa estrutura cristalina requer condições de altas pressões e/ou baixas temperaturas. A formação e a aglomeração de hidratos podem causar o bloqueio de linhas de transporte de óleo e/ou gás, reduzindo a eficiência do processo, danificando os equipamentos e comprometendo a segurança da parte operacional. Neste cenário, no presente trabalho é apresentado o estudo numérico-experimental de equilíbrio de fases dos hidratos para identificar as regiões de formação e adequar as condições de operação na indústria petrolífera. Para a predição das condições de formação dos hidratos é desenvolvido um modelo termodinâmico baseado na teoria de sólido ideal de van der Waals e Platteeuw. O modelo é fundamentado na igualdade dos potenciais químicos de todas as espécies em todas as fases (água líquida, hidrato e vapor). Para os cálculos de equilíbrio da fase hidrocarboneto foi utilizada a equação de estado de Soave Redlich-Kwong e o método da secante foi utilizado para solucionar o modelo iterativamente. As medidas experimentais foram realizadas utilizando metano puro e a mistura metano (90 % em mol) e dióxido de carbono e os testes foram realizados em duas bancadas distintas, sendo os procedimentos realizados semelhantes, baseados no método isocórico pela monitoração da resposta da pressão do sistema com a variação da temperatura. Os resultados experimentais e numéricos obtidos foram comparados com dados da literatura com a finalidade de validar o modelo termodinâmico proposto, o aparato experimental e o procedimento adotado. O erro absoluto máximo entre os resultados obtidos experimentalmente e do modelo termodinâmico desenvolvido foi de 0,57%. Desta forma, nota-se os resultados apresentaram boa concordância entre os dados experimentais e os da modelagem numérica.
Hydrates are crystalline structures composed by molecules of water or liquid and gas, and the crystal structure that requires stabilization conditions of high pressure and/or low temperatures. The formation and agglomeration of hydrates can cause blockage of transmission lines oil and / or gas, reducing process efficiency, damaging the equipment and compromise the safety of the operating part. In this scenario, in this paper the numerical-experimental study of phase equilibria of hydrates is presented to identify the regions of formation and adjust the operating conditions in the oil industry. To predict hydrate formation conditions of a thermodynamic model based on the ideal solid solution theory by van der Waals and Platteeuw is developed. The model is based on the equality of the chemical potentials of all species in all phases (liquid water, vapor and hydrate). The SoaveRedlich-Kwong equation of state was employed for the phase equilibrium properties of the hydrocarbon fluid phase and the secant method was used to solve the model iteratively. Experimental measurements were performed using pure methane and methane mixture (90 mol%) and carbon dioxide, and the tests were performed on two separate stands, and similar procedures performed based on the isochoric method by monitoring the pressure response of the system with changes in the temperature. The experimental and numerical results were compared with literature data in order to validate the proposed thermodynamic model, the experimental apparatus and procedure adopted. The maximum absolute error between the experimental results and thermodynamic model was 0.57%. Thus, the results showed good agreement between experimental data and numerical modeling.

Methane (CH4) and carbon dioxide (CO2) are two important greenhouse gases. Recent studies have shown that lakes, although they cover a small area of the globe, can be very important natural sources of atmospheric CH4 and CO2. It is therefore important to monitor the fluxes of these gases between lakes and the atmosphere in order to understand the processes that govern the exchange. By using the eddy covariance method for lake flux studies, the resolution in time and in space of the fluxes is increased, which gives more information on the governing processes. Eddy covariance measurements at a Swedish lake revealed a diel cycle in the fluxes of both CH4 and CO2, with higher fluxes during nighttime than daytime. The high nighttime CO2 fluxes could to a large extent be explained with enhanced transfer velocities due to waterside convection. For the diel cycle of CH4 flux it was suggested that waterside convection could enhance the transfer velocity, transport CH4 rich water to the surface, as well as trigger ebullition. Simultaneous flux measurements of CH4 and CO2 have been presented using both the eddy covariance method and the floating chambers method of which the latter is the traditional measuring method for lake fluxes. For CO2 the two methods agreed well during some periods but differed considerably during others. Disagreement between the methods might be due to horizontal heterogeneity in partial pressure of CO2 in the lake. The methods agreed better for the CH4 flux measurements. However, it is clear that due to the discontinuous nature of the floating chambers, this method will likely miss important high flux events. The main conclusions of this thesis are: 1) the two gas flux methods are not directly comparable and should be seen as supplementary to each other 2) waterside convection enhances the fluxes of both CH4 and CO2 over the water-air surface. If gas flux measurements are not conducted during nighttime, potential high flux periods might be missed and estimates of the total amount of gas released from lakes to the atmosphere may be biased.

Carbon dioxide hydrates were synthesized in a 0.10m I.D. and 1.22m tall bubble column equipped with a cooling jacket for heat removal. Visual observations at different driving forces (pressures between 2.75 and 3.60 MPa and temperatures between 0 and 8ºC) were recorded with a digital camera through a sight glass of 118.8 by 15.6 mm. The superficial gas velocity was varied from 20 to 50 mm/s to attain different levels of turbulence in the liquid. The growth rate was found to be dependent on the sequence/method used to reach the operating temperature and pressure. A greater supersaturation was obtained when the system temperature and pressure were reached with very low or no bubble-induced mixing. As a result, hydrates nucleated and grew immediately when starting the gas flow with the reactor volume being quickly filled with hydrates. Moreover, the hydrate growth rate and solution final density were higher when operating conditions partially condensed CO2 resulting in greater interphase mass transfer rates. In parallel, since hydrate formation is an exothermic process and the reaction is often limited by the rate of heat removal, heat transfer measurements were achieved in a simulated hydrate environment. The instantaneous heat transfer coefficient and related statistics gave insight on the role of bubbles on heat transfer and hydrodynamics.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 125-138).
Tropical peatlands in Southeast Asia have sequestered carbon over thousands of years and are an important global carbon stock. In natural peat swamp forests, high water levels inhibit decomposition due to anoxic conditions. However, they are being rapidly deforested and drained, releasing stored carbon to the atmosphere. In this thesis, we investigate the carbon dioxide and methane fluxes from both pristine and degraded peat swamp forests in Borneo using field measurements, modeling and remote sensing. We first study methane fluxes from natural peatlands. We use an isotope-based mass transport model to evaluate the extent of methane production, transport and oxidation. We find an order of magnitude more methane is produced than surface fluxes suggest. This dissolved methane is transported belowground to the rivers and streams draining peatlands. However, much of this methane is oxidized before reaching the atmosphere. We then study CO₂ emissions from peatlands. At the local scale, we use automated soil respiration chambers to assess how CO₂ emissions depend on temperature and water table. At a regional scale, we use remote sensing to investigate carbon losses due to peatland degradation. Drainage of peatlands enables peat decomposition and results in subsidence of the land surface. We track this subsidence using InSAR satellite data and use it to quantify regional CO₂ emissions. The spatial resolution of our technique allows us to uncover correlations with past and present land uses and peatland hydrology.
by Alison May Hoyt.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Civil and Environmental Engineering

Rising global temperatures are expected to increase concentrations of greenhouse gases emitted by northern latitudes within the current century. The impact of global warming on Arctic lacustrine systems is generally unknown, although recent studies have examined fluxes of carbon dioxide (CO₂) and methane (CH₄) produced in ebullition events. Few studies have investigated the added impact of atmospheric warming on lake sediments, which produce CO₂ and CH₄ through microbial decomposition and diffusive loss in the water column. To better understand carbon emission scenarios at elevated temperatures, sediment samples from Abisko, Sweden were analyzed for CO₂ and CH₄ production rates through incubation studies, and for concentrations of dissolved inorganic carbon (DIC) and dissolved CH₄ in sediment and porewater. Results showed that room temperature incubations emitted concentrations of CO₂ and CH₄ up to five times greater than those emitted by +5°C incubations. Furthermore, documented peat emissions were one to two orders of magnitude lower than the lake sediment incubation emissions reported in this paper. This study provides some of the first point source microbial emissions by lake sediment depth, and highlights that northern latitude sediments could have unprecedented effects on current spatial and temporal projections of Arctic warming.

Several heterogeneous catalysts were studied for synthesis gas production through dry reforming of methane (DRM). This process uses carbon dioxide in lieu of the steam that is traditionally used in conventional methane reforming to produce hydrogen that can then be repurposed in more chemical processes [2]. The monometallic catalysts explored were Ni/Al₂O₃ and Ni/CeZrO₂ followed by their bimetallic versions PtNi/Al ₂O₃ and PtNi/CeZrO₂ at 800°C. In addition to these catalysts, platinum supported Zeolitic Imidazolate Framework (ZIF)-8 was also investigated in comparison with PtNi/CeZrO₂ at 490°C. The studies suggest that these catalysts are suitable for promoting the dry reforming of methane for hydrogen production.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009.
Sequestration of carbon dioxide, CO2, has received large interest as a viable option for mitigating the high atmospheric concentrations of this greenhouse gas. Each year 25 gigatons of anthropogenic CO2 (7.3 GtC/yr) are released into the earth’s atmosphere with the combustion of fossil fuels being the major contributing source. Research in the field of sequestration technology involves evaluating various geological structures as possible reservoirs, determining adsorption capacities of natural formations and developing methods for carbon dioxide injection and the monitoring thereof. Identified potential CO2 reservoirs for geological carbon sequestration (GCS) include saline formations, depleted oil and gas fields and deep coal seams. Carbon dioxide sequestration in coal seams provides the economic opportunity of enhanced coalbed methane (CH4) recovery (ECBM). In South Africa, some coal seams are considered a viable option for long term CO2 sequestration projects as they are abundant and closely situated to South Africa’s largest concentrated CO2 point sources. Many studies have been conducted to determine the sorption capacities for methane and carbon dioxide gases on various coals from around the world; however, similar data have not been recorded for South African coals. The objectives of this study are to determine the adsorption capacities for methane and carbon dioxide of three South African coals over a pressure range of 0 – 50 bar. In the study, single-component gas adsorption experiments were conducted and the absolute adsorption capacities are reported. Isothermal adsorption experiments were conducted using both the volumetric and gravimetric methods with the volumetric apparatus pressure range extending up to 50 bar and the gravimetric apparatus up to 20 bar. Carbon dioxide adsorption capacities are much higher than the methane adsorption capacities, which are expected. Gravimetric experiments produce greater adsorption capacities than the volumetric method. However, the relative CO2/CH4 ratios for each coal, as well as the relative CO2/CO2 ratios between coals, remain almost identical. The difference in adsorption capacity is attributed to the strength of the vacuum pump used on each apparatus. The gravimetric apparatus makes use of a much stronger vacuum pump which can thus evacuate the coal pores more adequately than in the volumetric apparatus. The methane and carbon dioxide adsorption capacities of the three moisture-free coals compare well with literature data. The adsorption isotherms fit conventional adsorption models (the Langmuir and Freundlich adsorption equations) extremely well thus indicating that monolayer adsorption takes place. Since no internationally recognised testing standards are in place regarding adsorption procedures on coal, it is very difficult to compare adsorption results presented in the literature. Respective researchers determine their own experimental conditions for the many variables in coal adsorption studies. It is recommended that international testing standards be set in place to make coal research comparable. Such efforts would aid the development of a coal adsorption database, another recommendation, which would advance sequestration technology exchange and eliminate duplication of research efforts. The objectives of the project were achieved by determining the absolute adsorption capacities for carbon dioxide and methane gas of the three South African coals within a pressure range of 0 – 50 bar. Further work is required to investigate adsorption capacities of South African coals under supercritical conditions (above 73 bar abs and 31.1 oC).

Thesis (M.S.)--West Virginia University, 2001.
Title from document title page. Document formatted into pages; contains xv, 155 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 120-123).

L’étude concerne un nouveau procédé de reformage du gaz naturel en gaz de synthèse par le dioxyde de carbone (RSM), en vue de l'utilisation rationnelle des déchets carbonés industriels pour la production d'hydrocarbures et d'hydrogène. Cette méthode utilise des systèmes à membranes catalytiques inorganiques (SMC) qui favorisent des réactions catalytiques hétérogènes en phase gazeuse dans des micro-canaux céramiques. La surface active des catalyseurs formés à l'intérieur des canaux est faible en termes de superficie, mais elle est caractérisée par une valeur élevée du facteur Surface/Volume du catalyseur, qui induit une efficacité importante de la catalyse hétérogène. Les SMC, formés à partir de dérivés alcoxy et des précurseurs métalliques complexes, contiennent de 0,008 à 0,055% en masse de nano-composants mono- et bimétalliques actifs répartis uniformément dans les canaux. Pour les systèmes [La-Ce]-MgO-Ti02/Ni-Al et Pd-Mn-Ti02/Ni-Al, les productivités de 10500 et 7500 1/h·dm3membr. ont été respectivement obtenues lors du RSM dès 450°C avec une composition de gaz de synthèse H2/?? allant de 0,63 à 1,25 et un taux de conversion de 50% de la charge CH4/CO2 (1/1). Ainsi les SMC sont d’un ordre de grandeur plus efficace qu’un réacteur à lit fixe du même catalyseur. Le RSM est initié par l'oxydation de CH4 par l'oxygène de structure des oxydes métalliques présents en surface, et le CO2 réagit avec le carbone finement divisé provenant de la dissociation de CH4. Une synergie catalytique a été mise en évidence pour le système Pd-Mn. Ces SMC de 108 pores par cm² de surface constituent un ensemble de nano réacteurs de fort potentiel industriel (synthèse d’oléfines, biomasse)
This study reports the development of a new process to convert methane and carbon dioxide (dry methane reforming - DMR) into valuable products such as syngas from non-oil resources. The practical interest is to produce syngas from carbon containing exhaust industrial gases. This process uses membrane catalytic systems (MCS) that support heterogeneous catalytic reactions in gaseous phase in ceramic micro-channels. The active surface of the catalysts formed inside the micro-channels is low in term of area, but it is characterized by a high value of the catalyst surface/volume ratio, which induces a high efficiency of heterogeneous catalysis. The SMC are formed from alkoxy derivatives and precursor metal complex containing between 0.008 and 0.055% by weight of nano-components mono-and bimetallic active distributed evenly in the channels. For systems [La-Ce] -MgO-Ti02/Ni-Al and Pd-Mn-Ti02/Ni-Al, productivities of 10500 and 7500 l/h · dm3 membr. were respectively obtained by RSM at 450°C with a composition of syngas H2/?? ranging from 0.63 to 1.25 and a conversion rate of 50% with a CH4/CO2 (1/1) feed. Thus the CMS is an order of magnitude more efficient than a fixed bed reactor of the same catalyst. The MDR is initiated by the oxidation of CH4 by structural oxygen of metal oxides available on the surface, and the CO2 reacts with the finely divided carbon arising from the dissociation of CH4. A catalytic synergy has been demonstrated for the system Pd-Mn. This CMS, having 108 pores per cm² of surface, can be considered as a set of nano reactors. Thus this new approach is very promising for industry (synthesis of olefins, uses of biomass)

Wetland carbon sequestration is offset by carbon dioxide (CO₂) and methane (CH₄) emissions for which the magnitudes remain coarsely constrained. To better understand the spatial and temporal variations of gaseous carbon fluxes from marsh soils in a Mediterranean climate, I collected air and soil samples over the course of 10 months at Carpinteria Salt Marsh Reserve (CSMR) located in the County of Santa Barbara, California. The CSMR consists of four zones characterized by differences in elevation, tidal regime, soil properties, and vegetation. Twelve static chambers were deployed among two lower marsh zones, a mudflat, and a marsh-upland transition zone for fortnightly flux measurements from September 2015 to May 2016. In August 2015 and June 2016, soil cores up to 50 cm deep were extracted near the chambers, segmented by depth, and analyzed for soil moisture, bulk density, particle size distribution, electrical conductivity, pH, organic/inorganic carbon, and total nitrogen content. Averaged over the 9-month study period, the marsh-upland transition zone had the highest CO₂ fluxes at 5.3 ± 0.7 g CO₂ m^–2 d^–1 , followed closely by the lower marsh zones (3.8 ± 0.6 g CO ₂ m^–2 d^–1 and 2.8 ± 0.7 g CO₂ m^–2 d^–1), which were one order of magnitude higher than the CO₂ fluxes from the mudflat (0.4 ± 0.1 g CO₂ m^–2 d ^–1). The CO₂ fluxes varied significantly on a seasonal scale but were not consistently correlated with environmental variables measured. The CH₄ fluxes had no clear seasonal patterns, but overall CH ₄ flux rates from the lower marsh zones (2.2 ± 1.5 mg CH ₄ m^–2 d^–1 and 1.9 ± 0.2 mg CH₄ m^–2 d^–1) surpassed those from the mudflat (0.2 ± 0.06 mg CH₄ m^–2 d^–1) by an order of magnitude, and the marsh-upland transition zone was a net methane sink (-0.07 ± 0.1 mg CH₄ m^–2 d^–1). The CH₄ fluxes correlated well with most soil properties by zone. Our results show that soil gaseous carbon fluxes from a coastal salt marsh vary by salt marsh zone.

Le dioxyde de carbone (CO2), principal contaminant des gaz naturels bruts et du biogaz doit être extrait en vue d’un enrichissement en méthane (CH4) compatible avec les spécifications d’injection en réseaux de gaz naturel. Au cours des dernières années, une famille de matériaux poreux de type réseaux organométalliques à base de magnésium (Mg-MOF-74) a ouvert une nouvelle perspective à cet effet en raison d’une excellente affinité des sites métalliques exposés au sein de la structure cristalline pour l’adsorption du CO2. Ce matériau est un adsorbant potentiellement bon candidat pour l’enrichissement en CH4 de gaz naturel et de biogaz par des procédés opérant en modulation de pression. La présente étude propose d’examiner l’amélioration des performances d'adsorption du CO2 en mélange avec le CH4 par dopage du matériau Mg-MOF-74 avec des nanotubes de carbone et de l'oxyde de graphène. L'objectif est d'améliorer les propriétés texturales pour favoriser la diffusion des molécules des gaz dans les micropores et leur accessibilité aux sites d'adsorption. Les matériaux ont été synthétisés sous réaction solvothermique et caractérisés par DRX, IRTF, MEB, ATG et physisorption d’azote à 77K. Les équilibres et énergies d'adsorption ont été mesurées suivant une méthode manométrique dans une gamme de pression allant jusqu'à 35 bar et à 25°C, 50°C et 75°C. La cinétique de sorption a été étudiée à partir d’expériences de manométrie et de la méthode dite « Zero Length Column » à 25°C, 50°C et 75°C. A une teneur optimisée à 0,3% en masse d’agent dopant, le modèle de Brunauer–Emmett–Teller montre que la surface spécifique des matériaux dopés est augmentée de plus de 21% par rapport à celle du matériau non-dopé. Les données d'équilibre indiquent que la capacité d’adsorption en CO2 est sensiblement améliorée pour les matériaux dopés dans toute la gamme opératoire étudiée, tandis qu’ils démontrent une sélectivité comparable ou améliorée, dépendante de la température
Carbon dioxide (CO2), which is the major contaminant present in raw natural gas and biogas need to be extracted to increase their methane (CH4) content and match the standards of pipeline injection. In recent years, a family of porous materials, magnesium-based Metal Organic Framework (Mg-MOF-74), has opened new perspectives for this purpose thanks to strong adsorption affinity of CO2 with exposed metallic sites in the crystalline network. This material is a potential good adsorbent candidate for the enrichment in CH4 of natural gas and biogas by Pressure Swing Adsorption processes. The present study proposes to examine the CO2 adsorption performances and separation ability from CH4 of Mg-MOF-74 materials doped with carbon nanotubes and graphene oxide. The objective is to improve the texture of the materials to promote the diffusion of gas molecules into micropores and their accessibility to adsorption sites. The materials were synthesized under solvothermal reaction and characterized by PXRD, FTIR, FESEM, TGA and physisorption of nitrogen at 77K. The adsorption equilibria and energies were measured using manometric method in a pressure range up to 35 bar and at 25°C, 50°C and 75°C. The sorption kinetics of CO2 and CH4 on the materials were studied from manometric experiments and using the Zero Length Column method at 25°C, 50°C and 75°C. At an optimized content of the doping agents of 0.3 wt%, Brunauer–Emmett–Teller model shows that the specific surface area is increased for both composites, by more than 21% compared to the pristine material. The equilibrium data indicates that the CO2 adsorption capacity is significantly improved in the whole range of operating conditions for both composites compared to the pristine material, whereas the CO2/CH4 adsorption selectivity appears either comparable or better as a function of temperature

Gas clathrate hydrates are inclusion compounds in which a guest gas molecule is trapped within a host cage made up of hydrogen-bonded water molecules 1. Sequestration of CO2 in dense hydrate form has been proposed as one solution for rising levels of CO 2 in Earth's atmosphere2. Recent research has predicted the existence of a high-density clathrate structure capable of realizing this goal3. In this thesis, powder x-ray diffraction of the CO 2-H2O system as a function of increasing pressure (0 to 2.5 GPa) at sub-ambient temperatures (250 to 260 K) was performed in pursuit of discovering novel high-density hydrates of CO2. In addition to previously reported clathrate structures4, CO2 FIS Ih, a non-clathrate structure previously unobserved in the CO 2-H2O system but reported in other systems5, was identified and characterized. Using similar experimental techniques, unrelated work on the structural stability of dickite, a layered silicate mineral, is also presented. *Please refer to dissertation for footnotes.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 18).
Soil is Earth's largest terrestrial carbon pool (Oertel et al., 2016) and can act as a net source of greenhouse gases (GHG). However, if organic material accumulates in soils faster than it is converted to CO2 by cellular respiration, soil becomes a smaller GHG source and even has the potential to become a GHG sink. Not much is known about factors that drive soil to be a source or a sink of GHG. Soil temperature and moisture have both been shown to correlate with CH4 emissions and temperature has been shown to correlate with CO 2 emissions (Jacinthe et al., 2015). Currently these relationships are not well constrained, particularly in upland soils, which are soils found at elevations between 100 and 500 m (Carating et al., 2014). Soil from the Harvard Forest was collected and used in two in-lab flux experiments to constrain the effect that soil moisture has on i.) the rate of CH4 and CO2 production/consumption and ii.) the fraction of injected CH4 that is oxidized to CO2 by soil microbes. The first experiment involved injecting vials containing soil samples with CH4 , taking an initial measurement with a residual gas analyzer (RGA), incubating for three days, and taking final measurements using the RGA. The results of this experiment indicated that cellular respiration is an important carbon source in these soils, with more CO2 coming from cellular respiration than from the oxidation of CH4. The second experiment involved injecting vials containing soil samples with CH4 and 14CH4 as a tracer, incubating for six days, and analyzing CO2 from each sample using a scintillation counter. This experiment showed a weak trend indicating that increased soil moisture may result in decreased CH4 oxidation. Results showed that decays per minute from the samples were lower than in a control. These results indicated that not all CO 2 from each sample was successfully captured and analyzed using the methods here. So while the trend may hold true, it should be supported by reconducting the experiment using a more reliable means of CO2 capture. The unexpected results from both experiments indicated that there is still much to be learned about the reactions that occur in these soils and how to perfect laboratory methods to study them.
by Alexa Jaeger.
S.B.

Peatlands play an important role in the global carbon cycle. With rising levels of CO2 and CH4 in the atmosphere, a greater understanding of the controls on the flux of these gases from peatlands is important. In recent years, many peatlands have undergone restoration in attempts to reverse the damage caused by drainage. Therefore, the long-term effects of restoration on CO2 and CH4 fluxes are poorly understood. Peatland management strategies need to take the long-term responses of gaseous fluxes into account, and several hypotheses on these responses have been developed, despite the lack of data in this area. Thorne and Hatfield Moors, two lowland raised bogs in Eastern England were subjected to drainage and peat extraction over several centuries. Restoration has occurred in stages on these peatlands (1997, 2003-2005, 2008), and there is also an area where restoration has not yet occurred, providing an excellent space-for-time substitution. Data showed that CH4 fluxes were significantly larger at the two older sites in comparison to the younger site. Net ecosystem exchange and values of global warming potential were all positive (release to the atmosphere), and on average were larger at the two older sites in comparison with the unrestored site. Diurnal variations in gaseous fluxes were also explored. Methane fluxes were significantly larger at night-time from areas dominated by Eriophorum spp., which suggests that CH4 fluxes measured during the daytime could be underestimations. Carbon dioxide fluxes measured at night-time were larger than any of the daytime measurements of ecosystem respiration, where night-time conditions were simulated using a shroud to block the light. Therefore, ecosystem respiration measurements taken during the daytime could be underestimations. Sphagnum cuspidatum samples showed no evidence of a symbiosis with methanotrophs. Neither drought nor submergence of the Sphagnum sub-samples had any significant effect on rates of methanotrophy. However, drought had a significant effect on rates of methanogenesis, with higher rates from sub-samples that had been allowed to dry out.

Recently, with the rapid development of human society, meeting energy demand and controlling climate change are becoming urgent issues. Carbon dioxide (dry) reforming of methane (DRM) has been considered as a promising technology as it utilizes greenhouse gas to provide high value added liquid fuel and chemicals coupling with a Fischer-Tropsch (F-T) process. In other words, this process can both improve supply of liquid fuel and eliminate global warming issues. Since deactivation of catalysts is the major obstacle for commercialization of this approach, deep understanding of this process and development of catalysts with high activity and stability are necessary to be studied. Firstly, a comprehensive thermodynamic analysis of DRM and its side reactions was performed to get a deep understanding of this process. Low CH4/CO2 ratios improve CH4 conversion and CO selectivity, but have negative influence on CO2 conversion and H2 selectivity. While, CH4 conversion, CO2 conversion (T ≥ 630°C), H2 selectivity CO selectivity and carbon formation are all enhanced at high pressures. Severe carbon formation is found at the temperature range of 546 and 703 °C, and carbon free regime is suggested under operating conditions of T ≥ 1000 °C, CH4/ CO2 mole ratio = 1 and pressure = 0.1 MPa. In addition, an index about the relationship of H2/CO mole ratio and operating conditions was established in this study. It is beneficial in both process efficiency and economics in practice as the index can be used to guide the selection of appropriate operating conditions to tune H2/CO mole ratio in syngas to satisfy different requirements of different F-T processes. As drying process has big influence on structure formation of catalysts, the effects of oven drying and vacuum freeze drying on the performance of Ni/Al2O3 in DRM were investigated. The sublimation process in vacuum freeze drying increased the BET surface area but maintain small and uniform pore structure which protect NiO particle from aggregation. Besides, since the solid ice settled nickel nitrate salt in preparation stage, the aggregation of NiO after calcination is also suppressed. Comparing to oven dried catalyst (OD-Cat), anti-deactivation of vacuum freeze dried catalyst (VFD-Cat) was enhanced, which is due to small Ni particle size and high Ni dispersion. The CO2-TPD analysis shows that the amount of basicity on catalyst VFD-Cat is more than it on catalyst OD-Cat, which helps to eliminate coke formation by enhanced the adsorption and activation of CO2. Furthermore, less carbon deposition and less graphic degree coke was detected on spent catalyst VFD-Cat. Overall, vacuum freeze drying technique is suggested to synthesis catalysts for DRM to improve its stability and resistance of coke formation. In this study, the effects of calcination method (i.e. microwave and furnace) on activity and stability of catalyst Ni/Al2O3 were also studied. Microwave calcined catalyst (MC-Cat) showed a better catalytic performance than furnace calcined catalyst (FC-Cat) because of a slow deactivation rate. Because of the advantage of homogeneous volume heating in microwave calcination process, lager total surface area of catalyst and smaller Ni particle with uniform size were observed on catalyst MC-Cat than it on catalyst FC-Cat. Moreover, the amount of basic sites on catalyst MC-Cat was increased under microwave heating, which is contribution to coke formation with less amount and lower graphic degree. Therefore, microwave calcination is suggested to improve the resistance of catalytic deactivation caused by coke deposition. Additionally, the energy saving is more than 90% for microwave calcination in this case as microwave heating is a fast and energy efficiency. To improve the stability of catalyst Ni/γ-Al2O3 in carbon dioxide reforming of methane, K2CO3 was introduced as a promoter to enhance the coke resistance of catalyst. From the results, catalyst promoted with K2CO3 (K-Ni-Al) showed a relative high activity and stability in 100 h of DRM reaction. During long term test, the activity decreased at first 20h then became stable. As K2CO3 has advantages such as high specific heat, good thermal stability, strong basicity and fast heat transfer, it can increase basicity on the surface, control Ni particle size during both reduction and reaction stages, and increase the number of active metallic Ni by weaken the metal-support interactions. Moreover, it was found that that K2CO3 could react with carbon deposition, which could build a micro-cycle to eliminate coke formation.

Carbon dioxide CO₂capture through hydrate formation is a novel technology under consideration as an efficient means of separating CO₂from flue/fuel gas mixtures for sequestration and enhanced oil recovery operations. This thesis examines post-combustion capture of CO₂from fossil-fuel power plant flue-gas streams through hydrate formation in a silica gel column. Power plant flue-gas contains essentially CO₂and nitrogen (N2) after suitable pre-treatment steps, thus a model flue-gas comprising 17% co₂and 83% N2 was used in the study. Previous studies employed a stirred-tank reactor to achieve water-gas contact for formation of hydrates; recent microscopic studies involved using water dispersed in silica gel to react with gas, showing potential for improved hydrate formation rates without the need for agitation. This study focuses on macroscopic kinetics of hydrate formation in silica gel to evaluate hydrate formation rates, CO₂separation efficiency and determining optimal silica gel properties as a basis for a CO2 capture process. Spherical silica gels with 30.0 and 100.0 nm pore sizes and 40-75 and 75-200 μm particle sizes were studied to determine pore size and particle size effects on hydrate formation. 100.0 nm pores achieved higher gas uptake and CO₂recovery over the 30.0 nm case. Improved CO₂separation was obtained when 75-200 μm particles with 100.0 nm pores were used. The two effects observed are due to improved gas diffusion occurring with larger pore and particle size, favouring increased hydrate formation. Compared to stirred-tank experiments, results in this study show a near four-fold increase in moles of gas incorporated in the hydrate per mole of water, showing that improved water-to-hydrate conversion is obtained with pore-dispersed water. At similar experimental conditions, CO₂recovery improved from 42% for stirred-tank studies to 51% for the optimum silica (100.0 nm 75-200 μm) determined in this study. Finally, effects of tetrahydrofuran (THF) - an additive that reduces operating pressure were evaluated. Experiments with 1 mol% THF, the optimum determined from previous stirred tank studies, showed improved gas consumption in silica but reduced CO₂recovery, indicating that the optimum concentration for use in silica is different from that in stirred-tank experiments.

Reducing the rates of greenhouse gas (GHG) emissions is critical in combatting global climate change. Carbon dioxide (CO2) and methane (CH4) are the two most important carbon-based GHGs, for their atmospheric warming potential. Wetlands such as the Florida Everglades play major roles in the global carbon cycle, as varying hydrologic conditions lead to differential production rates of these two GHGs. This study measured CO2 and CH4 emissions in a re-created Everglades ridge-and-slough wetland, where water levels were controlled to reflect natural flood patterns. As expected, lower elevations were flooded longer and produced more CH4, while higher elevations produced more CO2. Since CH4 has a relatively high global warming potential, CO2 production would need to be 70 times that of CH4, to balance their GHG output. The average ratio of CO2 to CH4 across elevations was 22.0 (mol:mol), indicating that future water management within wetlands should consider GHG production potential.

Pacific Northwest coastal wetland extent has been significantly reduced due to development. To understand the effects of land use change on carbon cycling in coastal wetlands, we compared soil carbon dynamics in restored, disturbed (by diking or draining), and reference wetlands in both freshwater and saline conditions in Coos Bay, Oregon. We quantified soil carbon pools, measured in situ fluxes of methane (CH4) and carbon dioxide (CO2), and estimated sediment deposition and carbon sequestration rates. We found that land use change influences carbon cycling and storage in coastal wetlands. The disturbed marshes have likely lost all their organic material after draining or diking, except for a shallow A horizon. The restored marsh in situ CH4 and CO2 fluxes were intermediate between the disturbed and reference marshes. Generally, restored marshes showed a partial return of carbon storage functions, or an indication that reference level functions may be achieved over time.

The aim of the study is to investigate matrix-fracture interaction, gas oil gravity drainage (GOGD) and diffusion mechanisms with CO2, N2 and CH4 gas injection in a fractured system. Effects of injected gas type, initial gas saturation and diffusion coefficient on oil recovery are studied by an experimental and simulation work. In the experimental study, Berea sandstone cores are placed in a core holder and the space created around the core is considered as a surrounding fracture. System is kept at a pressure of 250 psi by CO2, N2 and CH4 gases and at a reservoir temperature of 70 °
C. Experiments with cores having similar initial saturations resulted in the highest ndecane recovery in CO2 experiment followed by CH4 and N2. The highest solubility of CO2 in n-decane and density difference between CO2 and CO2-ndecane mixture are considered as the reason of results. CO2 injection tests with n-decane and brine saturated core with and without initial gas saturation indicate that availability of initial gas saturation in matrix increased recovery. A simulation study is continued using CMG (Computer Modeling Group Ltd.) WinProp (Microsoft Windows&trade
based Phase-Behavior and Fluid Property Program) and GEM (Generalized Equation-of-State Model Compositional Reservoir Simulator). Simulation results of CO2 experiment with initial gas show that dominant effect of GOGD decreases and diffusion becomes more effective at final production stages. Simulation study indicates an immediate, sharp decrease in oil saturation in matrix. Oil in matrix migrates into fractures and moves downward as a result of GOGD with gas injection.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2007.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 176-189).
Limiting anthropogenic climate change over the next century will require controlling multiple substances. The Kyoto Protocol structure constrains the major greenhouse gases and allows trading among them, but there exist other possible regime architectures which may be more efficient. Tradeoffs between the market efficiency of all-inclusive policies and the benefits of policies targeted to the unique characteristics of each substance are investigated using an integrated assessment approach, using the MIT Emissions Prediction and Policy Analysis model, the Integrated Global Systems Model, and political analysis methods. The thesis explores three cases. The first case addresses stabilization, the ultimate objective of Article 2 of the UN Framework Convention on Climate Change. We highlight the implications of imprecision in the definition of stabilization, the importance of non-CO2 substances, and the problems of excessive focus on long-term targets. The results of the stabilization analysis suggest that methane reduction will be especially valuable because of its importance in low-cost mitigation policies that are effective on timescales up to three centuries. Therefore in the second case we examine methane, demonstrating that methane constraints alone can account for a 15% reduction in temperature rise over the 21st century.
(cont.) In contrast to conventional wisdom, we show that Global Warming Potential based trading between methane reductions and fossil CO2 reductions is flawed because of the differences in their atmospheric characteristics, the uncertainty in methane inventories, the negative interactions of CO2 constraints with underlying taxes, and higher political barriers to constraining CO2. The third case examines the benefits of increased policy coordination between air pollution constraints and climate policies. We calculate the direct effects of air pollution constraints to be less than 8% of temperature rise over the century, but ancillary reductions of GHGs lead to an additional 17% decrease. Furthermore, current policies have not had success coordinating air pollution constraints and CO2 constraints, potentially leading to a 20% welfare cost penalty resulting from separate implementation. Our results lead us to recommend enacting near term multinational CH4 constraints independently from CO2 policies as well as supporting air pollution policies in developing nations that include an emphasis on climate friendly projects.
by Marcus C. Sarofim.
Ph.D.

Soils contain the largest terrestrial organic carbon (C) stock, representing two-thirds or more of terrestrial C. Soils can act as a source or sink for carbon dioxide (CO???) and methane (CH???). One common technique for studying soil surface effluxes of CO??? (FCO???) and of CH??? (FCH???) is the soil chamber. This involves placing an enclosure over the soil surface and measuring the change in headspace concentration of the gas of interest over time. Due to the air-filled pore spaces within the near-surface soil, and adsorption of gases of interest onto chamber walls, the effective volume (Veff) of the chamber which contributes to FCO??? and FCH??? measurements is generally higher than the geometric volume (Vg) of the chamber. It is necessary that Veff be known in order to estimate fluxes accurately. This study coupled a flow-through non-steady-state automated chamber system to a laser-based cavity ring-down spectrometer (CRDS) to estimate Veff of the chamber system using separate standard additions of CO??? and CH??? calibration gases. The system was then mounted onto soil cylinders which had been filled with a forest soil from Vancouver Island, British Columbia, Canada. There has been recent interest in the ability of biochar to provide multiple environmental benefits upon application to soil, including the long-term sequestration of C. There are conflicting studies as to the effect of biochar on FCO??? and FCH??? and overall greenhouse gas (GHG) emissions. After making background measurements of FCO??? and FCH??? in soil columns, biochar was applied to one of the columns and the resulting FCO??? and FCH??? were measured. The results from this study showed that the coupling of the CRDS to the automated chamber system proved to be successful. The estimated Veff during CO??? and CH??? calibration gas injections agreed with past studies as the Veff was 5 to 10% larger than the geometric volume of the chamber. Following biochar application, the amended soil produced 36.9% more CO??? and consumed 20.4% less CH??? than the control over the four month experiment. The results showed that soil water content was an important factor in controlling FCO??? and FCH??? following biochar amendment.

In this dissertation the gas permeation process within four hybrid inorganic-organic membranes is modeled at the micro level using molecular dynamics (MD) and at the meso scale level using a diffusion mechanism. The predicted permeances and relative selectivity of CO₂ and CH₄ are compared with the experimental results. In the MD simulation a single-pore silica crystal framework model with and without inserted phenyl groups are used to define two membrane structures. We designate the two cases as PSPM and SPM respectively. To mimic the diffusion of gas across the membrane, a three-region system with a repulsive wall potential on the edge is employed. Results from the SPM model indicate that the pore size affects the permeance but not the selectivity. In the PSPM model the permeance decreases significantly when the pore size is below a critical value. The extent of decrease varies with the type of gas and this is reflected in the large selectivity in the PSPM model. When the initial diameter is 0.4 nm the model shows a selectivity of 17.3, which is very close to experimental results. At this selectivity the CO₂ permeance is 2.87 Ã 10^-4 mol m^-2s^-1Pa^-1 and the CH₄ permeance is 1.66 Ã 10^-5 mol m^-2s^-1Pa^-1. For different gases we also studied the motions of the phenyl groups in the pore during the permeation process. The results show that in CO₂ diffusion the phenyl groups moves in a larger range than in CH₄ diffusion. The density profile of gas molecules that the phenyl groups see is analyzed using double layer phenyl groups . The results show that the number of phenyl groups cannot affect the permeation. In the meso scale study a mixed mechanism model with a grid framework is developed to model the permeation process. In the model the membrane is assumed to consist of various grids which follow three major diffusion mechanisms. Models with different grid sizes are employed for the four membranes. Parameters in each model are estimated from the permeance results of the two gases. By comparing the estimated parameters in the surface diffusion mechanism with the reported values, the acceptable grid models are determined and the models with the minimum number of grids are studied. The diffusion is dominated by the activated Knudsen diffusion mechanism at lower temperatures and follows the surface diffusion mechanism when the temperature is above a critical value. In the diffusion of both gases within the four membranes the surface diffusion portion is very close but the activated Knudsen diffusion portion is not. This explains why the permeation with high selectivity occurs at lower temperatures. By comparing the results it shows the two studies can validate each other. On the other hand the two methods can be complementary as the diffusion model is able to predict the permeance within the right range and the MD model is able to predict the selectivity more accurately.
Ph. D.

Ice core records show that the atmospheric concentration of methane (CH₄) during the Last Glacial Maximum (LGM) was 40-50% lower than during the preindustrial Holocene. To understand this natural variation it is important to know how the sources and sinks of CH₄ change over time. Natural wetlands were the single largest contributor of CH₄ to the atmosphere in glacial times, yet models used to estimate their behaviour and CH₄ flux are largely based around relationships derived under modem day conditions. This thesis responds to this issue by exposing wetland mesocosms with contrasting nutrient availability, to the atmospheric concentration of carbon dioxide (CO₂) present at the LGM for 2 years. At the end of this experiment, total CH₄ flux was suppressed by an average of 29% in the nutrient rich fen (P < 0.05). In contrast, the nutrient poor bog showed no response to the treatment (P > 0.05). Further exploring the effects of CO₂ starvation showed that the fen ecosystem exhibited notable reductions in dissolved organic carbon, dissolved CH₄ and a change in the response of CH₄ flux to changing temperature, variables and relationships which all remained unchanged in the bog. The contrasting response of the two ecosystems to CO₂ starvation could be largely explained by differences in nutrient status, species composition and dominant CH₄ production pathways. In particular, it is hypothesised that bog plants under LGM CO₂ concentrations supplemented photosynthesis through the use of subsurface derived CO₂, thus counteracting the treatment effect. The results from this thesis suggest that the CH₄ source strength of late-glacial and early Holocene wetlands may currently be over-estimated because fen ecosystems are a far smaller CH₄ source under low atmospheric [CO₂] than they are today. Furthermore, the results provide new insights into the role of glacial atmospheric CO₂ concentrations in influencing CH₄ emissions from terrestrial ecosystems and provide empirical evidence for a connection between glacial-interglacial changes in atmospheric CH₄ and CO₂ concentrations observed in ice cores.

The influence water levels have on CO2 and CH4 efflux were investigated at the Loxahatchee Impoundment Landscape Assessment (LILA) research facility, located in Boynton Beach, FL, USA. Measurements of CO2 efflux were taken for 24 h periods four times for one year from study plots. Laboratory incubations of intact soil cores were sampled for CO2, CH4, and redox potential. Additionally, soil cores from wet and dry condition were incubated for determination of enzyme activity and macronutrient limitation on decomposition of organic matter from study soils. Water levels had a significant negative influence on CO2 efflux and redox, but did not significantly influence CH4 efflux. Study plots were significantly different in CH4 efflux and redox potential. Labile carbon was more limiting to potential CO2 and CH4 production than phosphorus, with the effect significantly greater from dry conditions soils. Enzyme activity results were variable with greater macronutrient responses from dry condition soils.

Carbon dioxide (CO2) and methane (CH4) fluxes from the soil surface, and concentrations within the soil profile, were measured between June 1998 and Sept. 1999 at four adjacent forest plantations and an old field in Nepean, Ontario. The objectives of this study were to quantify seasonal CO2 and CH4 fluxes from the soil surface and within the soil profile to determine the effect of soil moisture and temperature, and forest age and species on the exchange, and establish a chronosequence of organic carbon accumulation in the forest plantations and the old field soils.
Dynamic and static chamber techniques were used to measure surface fluxes of CO2 and CH4, respectively, and soil gas concentrations were sampled with probes. In the old field and forest plantations, surface soil CO2 flux ranged from 2.9 to 27 g CO2 m-2 d-1 and 2.0 to 39 g CO2 m -2 d-1 respectively. Significant differences due to age and species of plantation were observed. Seasonal variations in CO2 efflux from the soil surface and within the soil profile were related to variation in soil temperature and moisture. Uptake of CH4 was observed at all sites and there was no significant differences in flux due to vegetation type or age. Maximum rate of CH4 consumption was 6.3 mg CH4 m-2 d-1. Methane uptake was positively related to soil moisture conditions.
The carbon content of the soil increased in all sites following the establishment of vegetation on sandy parent material. Carbon content was greatest in the upper soil profile. Rates of carbon accumulation ranged from 109 to 426 g m-2 y-1. Soil carbon increased with increasing age of plantation during the first 30 years following the establishment of vegetation on parent material, but declined as the forest plantation matured.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 113-117).
Carbonated frozen foods are not common on the market due to the limited liquid water available to dissolve CO₂ . CO₂ clathrate hydrates can change this because CO₂ is trapped in crystalline water. The CO₂ flash-freezing process developed in this thesis forms CO₂ hydrates directly in a confection as it freezes. In this process, the confection mixture is dispersed in liquid CO₂; then the combined fluids are flashed to 10-20 bars. The mixture breaks up into small fragments, which rapidly crystallize into CO₂ hydrate (instead of ice) due to the intimate contact between mixture and evaporating CO₂ . This CO₂ hydrate formation results in a frozen, carbonated confection. CO₂ hydrates have a significant impact on packaging and storage requirements for the confection. This study shows that the minimum storage pressure is determined by the ice- CO₂ hydrate-gas equilibrium (IHG) curve, which does not change with the concentration of solutes in the aqueous phase. The minimum CO₂ content in a storage vessel is determined by the amount of CO₂ needed to avoid ice; in the presence of ice CO₂ can redistribute quickly, leading to an inhomogeneous product. Packaging must therefore be designed considering the significant CO₂ evolution from dissociating CO₂ hydrates during heat shock. Warming of a confection causes CO₂ hydrates to dissociate, even at pressures greater than the IHG pressure due to the requirement of chemical equilibrium between water in aqueous and crystalline phases. In packaging with limited heads pace, this CO₂ release increases the pressure significantly.
(cont.) When CO₂ hydrate confections are consumed CO₂ is strongly perceived both through tingling caused by carbonic acid and through tactile stimulation caused by bubbles. A higher concentration of CO 2 is required in CO₂ hydrate confections than in carbonated beverages for similar fizziness perception because a significant fraction of the CO₂ escapes when a consumer exhales. The CO₂ concentration in the melted confection does not exceed the solubility of CO₂ at atmospheric pressure, but ingredients in the recipe can modulate the growth of bubbles as the confection melts. Consumer testing is needed to define the form and style of CO₂ hydrate confection that should be pursued.
by Teresa Baker Peters.
Ph.D.

Fossil fuels constitute a significant fraction of the world’s energy demand. The burning of fossil fuels emits huge amounts of carbon dioxide into the atmosphere. Therefore, the limited availability of fossil fuel resources and the environmental impact of their use require a change to alternative energy sources or carriers (such as hydrogen) in the foreseeable future. The development of methods to mitigate carbon dioxide emission into the atmosphere is equally important. Hence, extensive research has been carried out on the development of cost-effective technologies for carbon dioxide capture and techniques to establish hydrogen economy. Hydrogen is a clean energy fuel with a very high specific energy content of about 120MJ/kg and an energy density of 10Wh/kg. However, its potential is limited by the lack of environment-friendly production methods and a suitable storage medium. Conventional hydrogen production methods such as Steam-methane-reformation and Coal-gasification were modified by the inclusion of NaOH. The modified methods are thermodynamically more favorable and can be regarded as near-zero emission production routes. Further, suitable catalysts were employed to accelerate the proposed NaOH-assisted reactions and a relation between reaction yield and catalyst size has been established. A 1:1:1 molar mixture of LiAlH4, NaNH2 and MgH2 were investigated as a potential hydrogen storage medium. The hydrogen desorption mechanism was explored using in-situ XRD and Raman Spectroscopy. Mesoporous metal oxides were assessed for CO2 capture at both power and non-power sectors. A 96.96% of mesoporous MgO (325 mesh size, surface area = 95.08 ± 1.5 m2/g) was converted to MgCO3 at 350°C and 10 bars CO2. But the absorption capacity of 1h ball milled zinc oxide was low, 0.198 gCO2 /gZnO at 75°C and 10 bars CO2. Interestingly, 57% mass conversion of Fe and Fe3O4 mixture to FeCO3 was observed at 200°C and 10 bars CO2. MgO, ZnO and Fe3O4 could be completely regenerated at 550°C, 250°C and 350°C respectively. Furthermore, the possible retrofit of MgO and a mixture of Fe and Fe3O4 to a 300 MWe coal-fired power plant and iron making industry were also evaluated.

Peatlands are multiservice ecosystems: they are the largest terrestrial store of carbon in the UK, unique habitats which provide a home for internationally important species and managed for forestry, farming and game management and shooting. This makes understanding the impact of management practices on their ecology important if they are to be sustainably managed for multi-benefits. Fire has long been used to manage peatlands in the UK to improve grazing and habitat provision for livestock and game. The effect of fire on carbon cycling in blanket bogs is of increasing concern as greenhouse gas emissions from land use is now an important management as well as political issue. Gaps however, still exist in our understanding of the controls on greenhouse emissions from blanket bogs and the impact fire may have on them both directly and indirectly by modifying vegetation composition and environmental conditions. The main objective of this research was to assess the effect of fire on greenhouse gas emissions by measuring methane and ecosystem respiration after burning at blanket bog sites across Scotland for a period of up to 3 years and relating changes in fluxes with changes in vegetation composition and abiotic conditions. In addition, the response of the Sphagnum layer to burning was assessed by looking at the recovery of Sphagnum capillifolium in the field and in a novel laboratory experiment. The indirect effects of fire on methane emissions were further investigated by a laboratory experiment devised to test if high temperatures would be fatal to methanotrophic bacteria in the Sphagnum layer, reducing methanotrophy, and thus a mechanism for fire to increase methane emissions in the short term. The results showed that methane emissions and ecosystem respiration were not significantly different in burnt plots when compared to adjacent unburnt plots at each of the three sites studies. Methane emissions were only weakly correlated to the position of the water table and neither methane fluxes or ecosystem respiration correlated with measures of vegetation composition and above ground biomass. Methanotrophy in Sphagnum was found to be difficult to detect, with a high temperature treatment having no significant effect on rates of methane oxidation. S. capillifolium was found to respond to fire by growing new auxiliary stems if the capitulum was consumed or irreversible damaged physiologically by temperatures experienced at the moss surface, with surface temperatures around 400oC with a temperature residency time of 30 seconds on artificially dried samples the most damaging, but not lethal, treatment. These results suggest that low severity fires which only consume the canopy vegetation, not penetrating the peat and leaving the moss layer mostly intact, do not have significant effects on methane emissions and ecosystem respiration in the short and medium term. In addition, it suggests that S.capillifolium can, under certain circumstances, survive a fire with the characteristics of those studied here. These findings reiterate that best practice burning guidelines must continue to ensure that burning is only carried out on blanket bog when conditions are conducive to fires with the characteristics studied here, which had little effect on important components of the carbon cycle and are survivable by at least one of the most common species of Sphagnum.

Inland waters such as streams and lakes have recently been found to be supersaturated with both carbon dioxide (CO2) and methane (CH4) – the high concentrations resulting in significant natural emissions of greenhouse gases (GHGs). Previous studies have shown that streams emit particularly large amounts of GHGs per area covered, but the spatial variability is very high and has rarely been studied in detail. This study focuses on the variability of aquatic CO2 and CH4 concentrations with high spatial resolution in a hemi-boreal stream. The study area is a 7 km2 catchment in Skogaryd in southwest Sweden. 131 samples were collected and the stream was divided into groups depending on slope gradient and geographical placement. The results show that the concentrations had high spatial variability, especially regarding CH4, and that the concentrations are higher and more variable at lower slope gradients, which possibly indicates an increased gas exchange at higher slopes. The results also showed that concentrations can increase or decrease sharply over short distances in relation to changing slope gradient. This shows that frequent spatial sampling is needed to more accurately represent streams than what is often the case in many studies. A general distance between sampling locations could not be found due to the high variability of concentrations. Instead, the authors suggest that future studies of CO2 and CH4 concentrations in streams use a stratified random sampling strategy based on slope gradients.

The transformation of the current energy model towards a more sustainable mix, independent of fossil fuels, requires the exploration of new technologies that are capable of taking advantage of excess electricity derived from renewable energy sources and to use new alternative sources of carbon for the generation of clean fuels. An alternative that combines both is the Power-to-Gas (P2G) technology, whose concept is based on a two-stage process. In the first stage, excess electricity from renewable energies is converted to hydrogen by electrolysis. Then, in a second stage, the H2 produced is transformed to CH4 through methanation with CO2. The CH4 produced is referred to as synthetic natural gas (SNG) and allows large amounts of renewable energy to be distributed from the energy sector to the end-use sectors. The thermo-chemical CO2 methanation process is considered the most efficient route for large-scale SNG production. However, developing a cost-effective CO2 methanation technology is one of the biggest challenges facing the P2G concept. In this context, this thesis focused on the catalyst and reactor design for CO2 methanation. The thesis objectives were addressed in three main aspects, which are: i) design a high-performance catalyst based on metal oxide-promoted Ni/γ-Al2O3 and determine its reaction mechanism; ii) evaluate the stability of the catalyst and the tolerance to sulfur for its implementation in a relevant industrial environment (CoSin project); and finally, iii) develop a CFD model based on experimental kinetic data to understand the role of operating conditions and propose a new reactor configuration. In the first Chapter of this thesis it is presented a general introduction of the SNG production through CO2 methanation process. In the second Chapter, the addition of a promoter (X) on a system composed by Ni and γ-Al2O3 microspheres was studied as the design strategy to develop a micro-sized Ni-X/γ-Al2O3 catalyst. The catalysts based on Ni-CeO2/γ-Al2O3 was proposed as the most feasible due to its high catalytic performance in relation to its economic competitiveness. The optimal composition of each component of the Ni-CeO2/γ-Al2O3 was found through a systematic experimental design. The catalyst composed by 25wt.%Ni, 20wt.%CeO2 and 55wt.%γ-Al2O3 proved to be the most active and stable thanks to its enhanced Ni dispersion and reduction, its high metallic area, and the formation of moderate base sites. In Chapter three, the thermal stability and tolerance to sulfur impurities on the Ni-CeO2/γ-Al2O3 catalyst was further studied using high temperatures and the presence of H2S on the reactants. The strong metal-promoter interaction and the favourable formation of Ce2O2S were revealed as the main causes of its high stability and tolerance to H2S, respectively. Additionally, the implementation of Ni-CeO2/γ-Al2O3 in a two-stage industrial methanation process was performed to evaluate its technical feasibility. The desired gas composition (≥92.5%CH4) was successful obtained using a decreasing temperature profile (T=450-275°C) and P=5bar·g. The high stability recorded during the 2000h of experimentation demonstrated that Ni-CeO2/γ-Al2O3 can be a competitive catalyst for CO2 methanation. Regarding to reactor design, in Chapter four, the design of a fixed-bed multitubular reactor on a Ni-CeO2-Al2O3 catalyst was evaluated for mid-scale SNG production. A CFD mathematical model based on experimental kinetic data was developed. A reactor tube with a diameter of 9.25mm and a length of 250mm was proposed, which should be operated at Tinlet=473K, Twall=373K, GHSV=14,400h-1 and P=5atm to achieve XCO2=99% with Tmax of 673K. On the other hand, a reactor tube (di=4.6mm and L=250mm) with a heat management approach based on free convection was proposed for small-scale SNG production. The optimal conditions were found at GHSV=11,520h-1, Tinlet=503K, P=5atm, and Tair=298K. The feasibility of the simulated reactor proposal was experimentally validated over the micro-sized Ni-CeO2/γ-Al2O3 (XCO2=93% and T=830-495K).
Power-to-Gas (P2G) es una tecnología prometedora para el almacenamiento de combustibles bajos en carbono. El concepto P2G implica la conversión de energía renovable en hidrógeno mediante electrólisis con la posibilidad de combinarlo con CO2 para producir metano (gas natural sintético, SNG). La producción de SNG mediante el proceso termoquímico de metanación de CO2 es particularmente interesante porque ofrece un combustible fácilmente transportable con un amplio mercado probado para aplicaciones de uso final de energía, calor y movilidad. Sin embargo, el desarrollo de una tecnología de metanación de CO2 rentable es uno de los mayores desafíos que enfrenta el concepto P2G. En este contexto, esta tesis se centró en el desarrollo de un catalizador y un reactor para la metanación de CO2. Los objetivos de la tesis se abordaron en tres aspectos principales, que son: i) diseñar un catalizador de alto rendimiento basado en Ni/The transformation of the current energy model towards a more sustainable mix, independent of fossil fuels, requires the exploration of new technologies that are capable of taking advantage of excess electricity derived from renewable energy sources and to use new alternative sources of carbon for the generation of clean fuels. An alternative that combines both is the Power-to-Gas (P2G) technology, whose concept is based on a two-stage process. In the first stage, excess electricity from renewable energies is converted to hydrogen by electrolysis. Then, in a second stage, the H2 produced is transformed to CH4 through methanation with CO2. The CH4 produced is referred to as synthetic natural gas (SNG) and allows large amounts of renewable energy to be distributed from the energy sector to the end-use sectors. The thermo-chemical CO2 methanation process is considered the most efficient route for large-scale SNG production. However, developing a cost-effective CO2 methanation technology is one of the biggest challenges facing the P2G concept. In this context, this thesis focused on the catalyst and reactor design for CO2 methanation. The thesis objectives were addressed in three main aspects, which are: i) design a high-performance catalyst based on metal oxide-promoted Ni/γ-Al2O3 and determine its reaction mechanism; ii) evaluate the stability of the catalyst and the tolerance to sulfur for its implementation in a relevant industrial environment (CoSin project); and finally, iii) develop a CFD model based on experimental kinetic data to understand the role of operating conditions and propose a new reactor configuration. In the first Chapter of this thesis it is presented a general introduction of the SNG production through CO2 methanation process. In the second Chapter, the addition of a promoter (X) on a system composed by Ni and γ-Al2O3 microspheres was studied as the design strategy to develop a micro-sized Ni-X/γ-Al2O3 catalyst. The catalysts based on Ni-CeO2/γ-Al2O3 was proposed as the most feasible due to its high catalytic performance in relation to its economic competitiveness. The optimal composition of each component of the Ni-CeO2/γ-Al2O3 was found through a systematic experimental design. The catalyst composed by 25wt.%Ni, 20wt.%CeO2 and 55wt.%γ-Al2O3 proved to be the most active and stable thanks to its enhanced Ni dispersion and reduction, its high metallic area, and the formation of moderate base sites. In Chapter three, the thermal stability and tolerance to sulfur impurities on the Ni-CeO2/γ-Al2O3 catalyst was further studied using high temperatures and the presence of H2S on the reactants. The strong metal-promoter interaction and the favourable formation of Ce2O2S were revealed as the main causes of its high stability and tolerance to H2S, respectively. Additionally, the implementation of Ni-CeO2/γ-Al2O3 in a two-stage industrial methanation process was performed to evaluate its technical feasibility. The desired gas composition (≥92.5%CH4) was successful obtained using a decreasing temperature profile (T=450-275°C) and P=5bar·g. The high stability recorded during the 2000h of experimentation demonstrated that Ni-CeO2/γ-Al2O3 can be a competitive catalyst for CO2 methanation. Regarding to reactor design, in Chapter four, the design of a fixed-bed multitubular reactor on a Ni-CeO2-Al2O3 catalyst was evaluated for mid-scale SNG production. A CFD mathematical model based on experimental kinetic data was developed. A reactor tube with a diameter of 9.25mm and a length of 250mm was proposed, which should be operated at Tinlet=473K, Twall=373K, GHSV=14,400h-1 and P=5atm to achieve XCO2=99% with Tmax of 673K. On the other hand, a reactor tube (di=4.6mm and L=250mm) with a heat management approach based on free convection was proposed for small-scale SNG production. The optimal conditions were found at GHSV=11,520h-1, Tinlet=503K, P=5atm, and Tair=298K. The feasibility of the simulated reactor proposal was experimentally validated over the micro-sized Ni-CeO2/γ-Al2O3 (XCO2=93% and T=830-495K).-Al2O3 promovido por óxido metálico y determinar su mecanismo, ii) evaluar la estabilidad del catalizador y la tolerancia al azufre para su implementación en un entorno industrial relevante (proyecto CoSin), and iii) desarrollar un modelo CFD basado en datos cinéticos experimentales para comprender el papel de las condiciones de operación y proponer una nueva configuración de reactor. En línea con estos objetivos, un catalizador ternario basado en 25wt.%Ni-20wt.%CeO2-55wt.%The transformation of the current energy model towards a more sustainable mix, independent of fossil fuels, requires the exploration of new technologies that are capable of taking advantage of excess electricity derived from renewable energy sources and to use new alternative sources of carbon for the generation of clean fuels. An alternative that combines both is the Power-to-Gas (P2G) technology, whose concept is based on a two-stage process. In the first stage, excess electricity from renewable energies is converted to hydrogen by electrolysis. Then, in a second stage, the H2 produced is transformed to CH4 through methanation with CO2. The CH4 produced is referred to as synthetic natural gas (SNG) and allows large amounts of renewable energy to be distributed from the energy sector to the end-use sectors. The thermo-chemical CO2 methanation process is considered the most efficient route for large-scale SNG production. However, developing a cost-effective CO2 methanation technology is one of the biggest challenges facing the P2G concept. In this context, this thesis focused on the catalyst and reactor design for CO2 methanation. The thesis objectives were addressed in three main aspects, which are: i) design a high-performance catalyst based on metal oxide-promoted Ni/γ-Al2O3 and determine its reaction mechanism; ii) evaluate the stability of the catalyst and the tolerance to sulfur for its implementation in a relevant industrial environment (CoSin project); and finally, iii) develop a CFD model based on experimental kinetic data to understand the role of operating conditions and propose a new reactor configuration. In the first Chapter of this thesis it is presented a general introduction of the SNG production through CO2 methanation process. In the second Chapter, the addition of a promoter (X) on a system composed by Ni and γ-Al2O3 microspheres was studied as the design strategy to develop a micro-sized Ni-X/γ-Al2O3 catalyst. The catalysts based on Ni-CeO2/γ-Al2O3 was proposed as the most feasible due to its high catalytic performance in relation to its economic competitiveness. The optimal composition of each component of the Ni-CeO2/γ-Al2O3 was found through a systematic experimental design. The catalyst composed by 25wt.%Ni, 20wt.%CeO2 and 55wt.%γ-Al2O3 proved to be the most active and stable thanks to its enhanced Ni dispersion and reduction, its high metallic area, and the formation of moderate base sites. In Chapter three, the thermal stability and tolerance to sulfur impurities on the Ni-CeO2/γ-Al2O3 catalyst was further studied using high temperatures and the presence of H2S on the reactants. The strong metal-promoter interaction and the favourable formation of Ce2O2S were revealed as the main causes of its high stability and tolerance to H2S, respectively. Additionally, the implementation of Ni-CeO2/γ-Al2O3 in a two-stage industrial methanation process was performed to evaluate its technical feasibility. The desired gas composition (≥92.5%CH4) was successful obtained using a decreasing temperature profile (T=450-275°C) and P=5bar·g. The high stability recorded during the 2000h of experimentation demonstrated that Ni-CeO2/γ-Al2O3 can be a competitive catalyst for CO2 methanation. Regarding to reactor design, in Chapter four, the design of a fixed-bed multitubular reactor on a Ni-CeO2-Al2O3 catalyst was evaluated for mid-scale SNG production. A CFD mathematical model based on experimental kinetic data was developed. A reactor tube with a diameter of 9.25mm and a length of 250mm was proposed, which should be operated at Tinlet=473K, Twall=373K, GHSV=14,400h-1 and P=5atm to achieve XCO2=99% with Tmax of 673K. On the other hand, a reactor tube (di=4.6mm and L=250mm) with a heat management approach based on free convection was proposed for small-scale SNG production. The optimal conditions were found at GHSV=11,520h-1, Tinlet=503K, P=5atm, and Tair=298K. The feasibility of the simulated reactor proposal was experimentally validated over the micro-sized Ni-CeO2/γ-Al2O3 (XCO2=93% and T=830-495K).-Al2O3 se propone como el más factible debido a su alto rendimiento catalítico en relación a su competitividad económica. La fuerte interacción metal-promotor y la formación favorable de Ce2O2S se revelaron como las principales causas de su alta estabilidad y tolerancia al H2S, respectivamente. Adicionalmente, su exitosa implementación en un proceso de metanación industrial de dos etapas demostró su viabilidad técnica. Finalmente, se propone un reactor multitubular para la producción de SNG a mediana escala. Por otro lado, para la producción de SNG a pequeña escala, se propone un nuevo diseño de reactor con un enfoque de gestión del calor basado en la libre convención.

Previous coreflood experiments show that CO2 sequestration in carbonate rocks is a win-win technology. Injecting CO2 into a depleted gas reservoir for storage also produces hitherto unrecoverable gas. This in turn helps to defray the cost of CO2 sequestration. This thesis reports the results from experiments conducted on a Berea sandstone core. The experiments include displacement experiments and unconfined compressive strength tests. The displacement experiments were conducted at cell pressures of 1500 psig and temperature of 60oC using a 1 foot long and 1 inch diameter Berea sandstone core. Pure CO2 and treated flue gas (99.433 % mole CO2) were injected into the Berea sandstone core initially saturated with methane at a pressure of 1500 psig and 800 psig respectively. Results from these experiments show that the dispersion coefficient for both pure CO2 and treated flue gas are relatively small ranging from 0.18-0.225 cm2/min and 0.28-0.30 cm2/min respectively. The recovery factor of methane at break-through is relatively high ranging from 71%-80% of original gas in place for pure CO2 and 90% to 92% OGIP for treated flue gas, the difference resulting from different cell pressures used. Therefore it would appear that, in practice injection of treated flue gas is a cheaper option compared to pure CO2 injection. For the unconfined compressive strength tests, corefloods were first conducted at high flowrates ranging from 5 ml/min to 20 ml/ min, pressures of 1700-1900 Psig and a temperature of 65oC. These conditions simulate injecting CO2 originating from an electric power generation plant into a depleted gas reservoir and model the near well bore situation. Results from these experiments show a 1% increase in porosity and changes in injectivity due to permeability impairment. The cores are then subjected to an unconfined compressive strength test. Results from these tests do not show any form of weakening of the rock due to CO2 injection.

CH$ sb4$ and CO$ sb2$ fluxes were measured in upland boreal forest soils, over the period May 16$ sp{ rm th}$ through Sept. 16$ sp{ rm th}$, 1994, among a variety of vegetation and drainage characteristics. Most upland soils consumed CH$ sb4$, (0.6 to $-$2.6 mg CH$ sb4$ m$ sp{-2}$ d$ sp{-1}$), and produced CO$ sb2$, (0.2 to 26.8 g CO$ sb2$ m$ sp{-2}$ d$ sp{-1}$). CH$ sb4$ consumption showed no seasonal trend, however CO$ sb2$ flux displayed an increasing rate until late August, after which flux rates began to decrease. Differences among the sites examined showed soil temperature and organic matter content to be the primary controls in predicting seasonal mean CH$ sb4$ flux rates. Similarly for CO$ sb2$ flux, soil temperature and C content proved to be the best predictors of seasonal mean differences among the range of sites examined.
Sites could be divided into 2 categories, strong CH$ sb4$ consuming and CO$ sb2$ producing sites, Gillam Aspen, Gillam Pine, OBS Aspen, Burn Moss, Palsa Birch, and YJP Dry and weak CH$ sb4$ consuming and CO$ sb2$ producing sites, Gillam Spruce, OBS Spruce, YJP Wet, Burn Spruce and Palsa Moss. The strong flux sites all exhibited similar trends in soil characteristics as they were the warmest, driest sites with faster nutrient cycling processes and thin ($ sim$2 to 10 cm) organic layers. The weak flux sites were colder, wetter, with slower nutrient cycling, and a thick organic/peat layer ($ sim$20 to 50 cm). The primary visual distinction between these two groups was the presence of a Sphagnum sp. ground cover, which was characteristic of weak CH$ sb4$ consuming and CO$ sb2$ producing sites.