By the everyday increasing enthusiasm for using renewable-sustainable sources in energy production area, focusing on one and optimizing it in the best possible way should be of much interest. Biogas production from anaerobic digestion of wastes is a well known energy source which could be applied more efficiently if the CO2portion of it would be upgraded to CH4as well. There is a methanation reaction which could convert carbon dioxide to methane with the use of hydrogenation. In this report, the effort is to simulate this methanation reactor which is a catalytic bed of ruthenium on alumina base. The temperature change and its’ effect on reaction kinetics and equilibrium, also deriving designing parameters for the catalyst bed are different tasks which was tried to be covered in this thesis work. Based on calculations, the reactor can operate isothermally or adiabatically. The point is that each method has its own cons and pros. For the isothermal case finally the optimum temperature to run the reaction is decided to be 600 K in 10 bar total pressure. In adiabatic case then it is understood to work on interstage cooling strategy which in given conditions came to the number of 6 for reactors and 5 for interstage cooling devices. Afterwards it is thought to apply some technical changes to conventional adiabatic method and recycle some part of the product to the entrance of the reactor and assist the conversion. In this method number of reactors would be reduced to 2 and one heat exchanger in the middle. Selecting the best process in large scale treatment, needs lots of economical analysis and detail design while in small scale condition the most preferred method to run the reaction is isothermal.

A titania-supported nickel catalyst was prepared and tested in methanation in order to evaluate its catalytic properties (activity, selectivity and specially, activity loss), and compare it with an alumina-supported nickel catalyst. The titania-supported catalyst did not only show higher stability than alumina, but also presented a different cause of deactivation, carbon formation. In addition, a kinetic model was obtained for the titania-supported catalyst, and a study of the effect of different operating conditions (temperature, composition and partial pressures of synthesis gas and water) on the deactivation rate and carbon formation of this catalyst was performed. / <p><strong></strong> </p>

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24105号 / 工博第5027号 / 新制||工||1784(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 江口 浩一, 教授 安部 武志, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Découverte en 1902, la méthanation du C02 reçoit un intérêt grandissant pour son application aux procédés de stockage d'énergie électrique nécessaires au développement des énergies renouvelables. Sa mise en œuvre requiert le développement de réacteurs catalytiques innovants répondant au cahier des charges de cette application. Ces travaux sont dédiés à l'étude et l'optimisation de trois types de réacteurs-échangeurs conçus au cours de cette thèse :-un réacteur à lit fixe annulaire, -un réacteur à lit fixe milli-structuré et un réacteur à mousses métalliques supports de catalyseur. Leurs performances globales sont déterminées expérimentalement. La désactivation du catalyseur est étudiée et ses causes identifiées. Une modélisation des trois réacteurs permet la simulation de leur fonctionnement. Les propriétés hydrodynamiques et thermiques de leurs structures internes et les vitesses de réaction sont caractérisées expérimentalement. Les résultats numériques des simulations sont comparés aux expériences et complètent l'étude du comportement des réacteurs. Les modèles identifiés permettent finalement d'étudier les limites et les potentiels de ces réacteurs. / Discovered in 1902, the C02 methanation is getting a growing interest for its application to electricity storage processes needed for the development of renewable anergies. lts implementation requires the development of innovative catalytic reactors compatible with the specifications of this application. The present work focuses on the study of three reactor-exchangers designed during this thesis: - an annular fixed bed reactor, a milli-structured fixed bed reactor and a reactor which uses metallic foams as catalyst carriers. Their global performances are experimentally evaluated. The catalyst deactivation is studied and its causes identified. A modeling of these three reactors allows the simulation of their behavior. The hydrodynamic and thermal properties of their internai structure and the reaction kinetics are experimentally characterized . The numerical results of the simulations are compared to the experimental data and complete the analysis of the reactors behavior.The identified models are finally used to study the limits and the potentialities of the reactors.

A potential route for converting different carbon sources (coal, natural gas and biomass) into synthetic fuels is the transformation of these raw materials into synthesis gas (CO and H2), followed by a catalytic step which converts this gas into the desired fuels. The present thesis has focused on two catalytic steps: Fischer-Tropsch synthesis (FTS) and methanation. The Fischer-Tropsch synthesis serves to convert synthesis gas into liquid hydrocarbon-based fuels. Methanation serves instead to produce synthetic natural gas (SNG). Cobalt catalysts have been used in FTS while nickel catalysts have been used in methanation.             The catalyst lifetime is a parameter of critical importance both in FTS and methanation. The aim of this thesis was to investigate the deactivation causes of the cobalt and nickel catalysts in their respective reactions.             The resistance to carbonyl-induced sintering of nickel catalysts supported on different carriers (γ-Al2O3, SiO2, TiO2 and α-Al2O3) was studied. TiO2-supported nickel catalysts exhibited lower sintering rates than the other catalysts. The effect of the catalyst pellet size was also evaluated on γ-Al2O3-supported nickel catalysts. The use of large catalyst pellets gave considerably lower sintering rates. The resistance to carbon formation on the above-mentioned supported nickel catalysts was also evaluated. Once again, TiO2-supported nickel catalysts exhibited the lowest carbon formation rates. Finally, the effect of operating conditions on carbon formation and deactivation was studied using Ni/TiO2 catalysts. The use of higher H2/CO ratios and higher pressures reduced the carbon formation rate. Increasing the temperature from 280 °C to 340 °C favored carbon deposition. The addition of steam also reduced the carbon formation rate but accelerated catalyst deactivation.             The decline in activity of cobalt catalysts with increasing sulfur concentration was also assessed by ex situ poisoning of a cobalt catalyst. A deactivation model was proposed to predict the decline in activity as function of the sulfur coverage and the sulfur-to-cobalt active site ratio. The results also indicate that sulfur decreases the selectivity to long-chain hydrocarbons and olefins. / <p>QC 20160817</p>

Syngas fermentation via gasification is a two-stage process, which contains gasification of feedstock into syngas and syngas bio-methanation by anaerobic microorganisms. This project is a study on syngas fermentation. The gasification feedstock can be difficult-to-degrade solid waste so; waste volumes are reduced while green energy is produced. The main target of this thesis was to study novel configurations of reverse membrane bioreactor (RMB) in order to retain microbial cells inside the digester and thereafter increase methane production. In the first experiment, microbial cells encased in PVDF sachets were proved to perform efficiently in batch mode in comparison to free cells at optimum temperature, 55 oC. Moreover, encased cells in co-digestion of syngas and organic waste exhibited higher methane amounts compared to pure syngas treatment. Encased cells were then tested in thermophilic semi-continuous process and showed better performance compared to the free cell reactor. The RMB containing encased cells retained successfully the cells during the 154 days of the experiment, while free cells were washed-out. The highest amounts of methane from RMB and the free cell reactor were produced during the 126th - 130th day (6 and 1.5 mmol/day, respectively). In the last experiment, a RMB containing 13 membrane layers of enclosed cells was studied and compared to a conventional reactor of free cells. The RMB performed successfully in syngas bio-methanation under semi-continuous conditions during 49 days. The highest methane amount produced was 10 mmol/day in both RMB and free cell reactor. / Program: Industriell bioteknik

Atmospheric CO2 concentrations are at their highest level on record. Scientific evidence has demonstrated a direct correlation between the rise of CO2 levels and an increase of the global median temperature (~1°C higher than compared to the pre-industrial revolution times) due to the greenhouse gas effect. The change in climate due to this rapid increase of CO2 levels is already negatively affecting our ecosystem and lives, with unpredictable consequences in the future. The main source of anthropogenic CO2 emissions is attributed to the combustion of fossil fuels for energy production and transportation. Global indicators signal that carbon-intensive fuels will continue to be utilized as a main energy source despite the rising implementation of renewable energy sources. In order to curb CO2 emissions, several carbon dioxide capture, utilization and sequestration (CCUS) technologies have been suggested. The current state-of-the-art CO2 capture technology utilizes toxic and corrosive aqueous amine solutions that capture CO2 at room temperature but require heating above the water boiling point temperatures to separate CO2 from the amine solution; the latter of which is to be recycled. Once the CO2 is purified, it is necessary to transport it to its sequestration site or an upgrading processing plant. These are complicated schemes that involve many energy-intensive and costly processes. To address the shortcomings of these technologies, we propose a Dual Function Material (DFM) that both captures CO2 and catalytically converts it to methane in-situ. The DFM consists of a catalytic metal intimately in contact with an alkaline metal oxide supported on a high surface area carrier. The process operates within the flue gas at 320°C for both CO2 capture and methane generation upon the addition of renewable H2. The catalyst is required to methanate the adsorbed CO2 after the capture step is carried out in an O2 and steam-containing flue gas. Ruthenium, rhodium, and nickel are known CO2 methanation catalysts, provided they are in the reduced state. All three were compared for performance under DFM flue gas conditions. Ni is a preferred methanation catalyst based on price and activity; however, its inability to be reduced to its active state after experiencing O2-containing flue gas during the capture step was an outcome determined in this thesis. The performance of a variety of alkaline adsorbents (“Na2O”, CaO, “K2O” and MgO) and carriers (Al2O3, CeO2, CeO2/ZrO2 (CZO), Na-Zeolite-X (Na-X-Z), H-Mordenite Zeolite (H-M-Z), SiC, SiO2 and ZrO2-Y) were also studied. Selection of the best materials was based on CO2 capture capacity, net methane production and hydrogenation rates that were evaluated with thermogravimetric analysis and in fixed bed reactor tests. Rh and Ru DFMs were effective methanation catalysts with Ru being superior based on capture capacity, hydrogenation rate and price. Ru remained active towards methanation even after exposure to O2 and steam-containing simulated flue gas. Alkaline adsorbents, in combination with reduced Ru, were tested for adsorption and methanation. Ru – “Na2O”/Al2O3 DFMs showed the highest rates for methanation although CaO is also a reasonable candidate with slightly lower methanation kinetics. To date, we have demonstrated that -Al2O3 is the most suitable carrier for DFM application relative to other materials studied. The Ni-containing DFM, pre-reduced at 650°C, was highly active for CO2 methanation. However, the hydrogenation with 15% H2/N2 is completely inactive after exposure to O2 and steam, in a flue gas simulation, during the CO2 capture step at 320oC. This thesis reports that small amounts of precious metal (≤ 1% Pt, Pd or Ru) enhance the reduction (at 320°C) and activation of Ni-containing DFM towards methanation even after O2 exposure in a flue gas. While ruthenium is most effective, Pt and Pd all enhance reduction of oxidized Ni. Another objective of this thesis was to investigate whether a portion of the Ru, at its current loading of 5%, could be replaced with less expensive Ni while maintaining its performance. The findings show that the main advantage of the presence of Ni is a small increase in CO2 adsorption and increase in methane produced, at the expense of a lower methanation rate. Extended cyclic aging studies corroborate the stable performance of 1% Ru, 10% Ni, 6.1% “Na2O”/Al2O3. Characterization methods were used to monitor physical and chemical changes that may have occurred during aging studies. Measurements of the BET surface area, H2 chemisorption, XRD pattern, TEM images and STEM-EDS mapping were utilized to study and compare the structural and chemical changes between fresh and aged Ru doped Ni DFM samples. While similar BET surface areas were observed for the fresh and aged samples, some redispersion of the Ru and Ni sites was confirmed via H2 uptake and the observed decreases in Ru and Ni cluster size in the aged sample in comparison to the fresh. XRD patterns confirm an almost complete disappearance of the NiOx and RuOx species and the appearance of catalytically active Ru0 and Ni0 peaks on the aged sample compared to the fresh one. Further details of these methods, findings and conclusions are described in this thesis.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21271号 / 工博第4499号 / 新制||工||1700(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 陰山 洋, 教授 江口 浩一, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The response to climate change must include decisive and collaborative solutions that minimize global CO₂ emissions and enable a shift to low-carbon energy (renewable electricity) and CO₂-derived chemicals and fuels. A major challenge of minimizing fossil fuel use is producing critical chemicals and fuels for heavy industry and transportation in novel ways. These traditionally fossil-derived products can be derived from CO₂ that is captured from point sources or the atmosphere. Reactive CO₂ capture is an emerging area of research that focuses on developing materials and processes for CO₂ capture and in situ conversion to valuable chemicals or fuels. By combining these two steps, costly and energy-intensive steps of conventional integrated capture and conversion schemes are eliminated, including sorbent regeneration, CO₂ purification, pressurization, and transportation. These operations typically drive up the cost of capture and conversion processes, making them less economically attractive. The dual function material (DFM) is an Al₂O₃-supported, nano-dispersed catalyst and sorbent combination that demonstrates both capture and catalytic conversion properties, making reactive capture possible. Feasibility of the 1% Ru, 10% “Na₂O”/Al₂O₃ DFM for CO₂ direct air capture (DAC) and in situ catalytic methanation (DACM) has been demonstrated in previous work. Recent work has prioritized advanced laboratory testing and laboratory aging of this DFM under a variety of simulated ambient capture climates to assess the advantages and limitations of the material. A monolith was used as a structured support for the DFM to minimize reactor pressure drop, a particularly relevant challenge for DAC applications where large volumes of air must be processed to separate the small volume of CO₂ (~ 400 ppm). Findings from DFM monolith studies (1% Ru, 10% “Na₂O”/Al₂O₃//monolith) were shared with an engineering partner to support scale up efforts. Laboratory-simulated DACM cycles consisted of DAC performed at various real-world simulated ambient conditions followed by catalytic methanation, where the DFM was heated to 300°C in 15% H₂/N₂. Simulated DAC included O2 and humidity, and a surprising finding showed significant enhancement of CO₂ adsorption due to humidity in the capture feed. The maximum CO₂ capture capacity of the DFM monolith was measured to be 4.4 wt% (based on the weight of DFM material) at 25°C with 2 mol% H₂O in the DAC feed. Aging studies revealed consistent CO₂ capture and CH₄ production after over 450 hours of cyclic DACM testing that included simulated ambient conditions. No signs of deactivation of either the “Na₂O” sorbent or Ru catalyst were observed. The light-off temperature (indicative of kinetic control) observed for catalytic methanation was constant between fresh and aged cycles. These findings verified the qualifications of the 1% Ru, 10% “Na₂O”/Al₂O₃//monolith for the DACM application and supported further advanced bench and pilot plant testing by our engineering collaborator. Additional parametric studies were conducted to evaluate the effects of varying humidity during DAC and revealed that a higher H₂O concentration in the DAC feed correlates with greater CO₂ captured and converted with no evidence of competitive adsorption between CO₂ and H₂O. Additionally, it was found that temperature changes within ambient range (0 – 40°C) played little role in varying CO₂ captured under dry conditions, whereas moisture was found to be a major driver of capture capacity. Furthermore, stable performance at a reference condition was always achieved after excursions to varying ambient conditions. DACM tests revealed 30 – 40% of captured CO₂ desorbs during the temperature swing step, which was attributed mainly to the slow heating rate and low H₂ content (15%) required for safe laboratory operation. Unreacted CO₂ was eliminated by shortening the DAC step and engaging partial capture capacity of the DFM. This mode of cycling is more representative of that which would be carried out at scale, as shorter adsorption durations capitalize on the fastest adsorption kinetics exhibited by a capture material. Consistent with reported literature, findings suggest that CO₂ is preferentially adsorbed to stronger capture sites at the onset of DAC that are better able to retain CO₂ during heat up. Though the DFM is not fully utilized, these partial capacity cycles demonstrated higher conversions to CH₄ and a more efficient use of the material that will require less downstream purification at scale.

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