Dissertations / Theses on the topic 'Carbon dioxide methanation'

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.

This Dissertation investigates the kinetics of CO2 methanation over nickel and cobalt catalysts. Methanation was studied for both Ni/γ-Al2O3 and Co/ZrO2 catalysts, which were synthesised using an incipient wetness impregnation technique and subsequently characterised using analyses based on gas adsorption, XRD, TPR and thermogravimetry. Separately a CO hydrogenation reaction, the Fischer-Tropsch process, was modelled numerically to examine the influence of mass transfer in practical, commercial pellets of catalyst. The kinetics of methanation was investigated for Ni/γ-Al2O3 over a wide range of reactant partial pressures using a gradientless, spinning-basket reactor operated in batch mode and in a laboratory-scale, continuous fixed-bed reactor. Langmuir-Hinshelwood kinetic models were developed to represent the observed kinetics in each reactor: these models were then compared. For the batch reactor, a rate expression based the dissociation of a chemisorbed CO intermediate being the rate-limiting step was found to be consistent with the experimental results. However, results from the fixed-bed suggested that the hydrogenation of an adsorbed C atom determined the rate of reaction. These differences in the kinetics on Ni/γ-Al2O3 between the fixed-bed and batch reactors suggest that a Langmuir approach using a single, rate-determining step may not be representative across all conversions. The rate over the Co/ZrO2 catalyst was characterised in the fixed-bed reactor over a range of reactant partial pressures at temperatures between 433 K and 503 K. The rate was observed to be dependent on hydrogen partial pressure and temperature, with the rate increasing with both. Previous research has reported a wide range of values of the apparent activation energy, with a study suggesting it was sensitive to pressure. Accordingly, the apparent activation energy was investigated for pressure sensitivity over a range of pressures between 5 and 15 barg: it was found to be constant. The values determined (~88-91±8 kJ/mol) were notably consistent with those reported for CO hydrogenation on cobalt. Kinetic schemes based on Langmuir-Hinshelwood and power law equations were evaluated, with the results best described by a reaction scheme based on the carbide pathway, with a rate-determining step of CH hydrogenation. A reaction-diffusion model of the Fischer-Tropsch process in a 2-D hollow cylinder was developed and analysed across a range of Thiele moduli and the extents of error in both effectiveness factor and selectivity were quantified relative to one-dimensional sphere and slab analogues. The errors between 2-D and 1-D analogues were found to be most significant between Thiele moduli of ~0.25 and ~3. Hollow cylinder effectiveness factors were bounded by those of sphere and slab above and below Thiele moduli of ~0.75 and ~1.15 respectively for the conditions examined, with the effectiveness factors exceeding those of both sphere and slab models between these moduli. A comparison of the hollow cylindrical pellets against spheres of equivalent volume demonstrated that hollow cylinders provided improved fixed-bed performance, with improved effectiveness factors and selectivities due to the lowered diffusion lengths of the hollow cylindrical geometry.

New Ni-based catalysts have been developed and applied for the steam dry reforming (SDR) and the methanation reaction of clean biogas, exploring the possibility of converting its CO2 fraction into a useful product (syngas or biomethane) instead of separating and discharging it. The catalysts were prepared from hydrotalcite-type precursors through co-precipitation, with the addition of promoters (Ru, Rh, La) or basic sorbents (CaO). Then, they were deeply characterised before and after reaction by BET, XRD, H2-TPR, CO2-TPD analyses, and Raman spectroscopy. The results obtained for SDR at low temperature (700°C) showed that, although the catalysts synthetised were active and stable in terms of CH4 conversion, the conversion values reached were not yet compatible with the industrial requirements. On the other hand, a promising Ni-Ru bimetallic catalyst was developed for high temperature SDR (900°C), presenting a convenient alternative to the already studied Ni-Rh and Ni-Ir formulations. The synergic effect of the two metals significantly enhanced the catalyst stability and resistance toward coke formation, while achieving high methane and carbon dioxide conversions and producing syngas with a H2/CO ratio compatible with downstream applications such as Fischer-Tropsch or methanol synthesis. Finally, the feasibility of the direct methanation of clean biogas was assessed, using a Ni-La catalyst. Its activity was studied simulating the industrial conditions for the reaction, achieving CO2 conversions up to 90% with a total selectivity for methane production.

[ES] La presente tesis doctoral se centra en el desarrollo de nuevas membranas de separación de gases, así como su empleo in-situ en reactores catalíticos de membrana para la intensificación de procesos. Para este propósito, se han sintetizado varios materiales, como polímeros para la fabricación de membranas, catalizadores tanto para la metanación del CO2 como para la reacción de síntesis de Fischer-Tropsch, y diversas partículas inorgánicas nanométricas para su uso en membranas de matriz mixta. En lo referente a la fabricación de las membranas, la tesis aborda principalmente dos tipos: orgánicas e inorgánicas. Con respecto a las membranas orgánicas, se han considerado diferentes materiales poliméricos, tanto para la capa selectiva de la membrana, así como soporte de la misma. Se ha trabajado con poliimidas, puesto que son materiales con temperaturas de transición vítrea muy alta, para su posterior uso en reacciones industriales que tienen lugar entre 250-300 ºC. Para conseguir membranas muy permeables, manteniendo una buena selectividad, es necesario obtener capas selectivas de menos de una micra. Usando como material de soporte otro tipo de polímero, no es necesario estudiar la compatibilidad entre ellos, siendo menos compleja la obtención de capas finas. En cambio, si el soporte es de tipo inorgánico, un exhaustivo estudio de la relación entre la concentración y la viscosidad de la solución polimérica es altamente necesario. Diversas partículas inorgánicas nanométricas se estudiaron para favorecer la permeación de agua a través de los materiales poliméricos. En segundo lugar, en cuanto a membranas inorgánicas, se realizó la funcionalización de una membrana de paladio para favorecer la permeación de hidrógeno y evitar así la contaminación por monóxido de carbono. El motivo por el cual se dopó con otro metal la capa selectiva de la membrana metálica fue para poder emplearla en un reactor de Fischer-Tropsch. Con relación al diseño y fabricación de los reactores, durante esta tesis, se desarrolló el prototipo de un microreactor para la metanación de CO2, donde una membrana polimérica de capa fina selectiva al agua se integró para evitar la desactivación del catalizador, y a su vez desplazar el equilibrio y aumentar la conversión de CO2. Por otro lado, se rediseñó un reactor de Fischer-Tropsch para poder introducir una membrana metálica selectiva a hidrogeno y poder inyectarlo de manera controlada. De esta manera, y siguiendo estudios previos, el objetivo fue mejorar la selectividad a los productos deseados mediante el hidrocraqueo y la hidroisomerización de olefinas y parafinas con la ayuda de la alta presión parcial de hidrógeno.
[CAT] La present tesi doctoral es centra en el desenvolupament de noves membranes de separació de gasos, així com el seu ús in-situ en reactors catalítics de membrana per a la intensificació de processos. Per a aquest propòsit, s'han sintetitzat diversos materials, com a polímers per a la fabricació de membranes, catalitzadors tant per a la metanació del CO2 com per a la reacció de síntesi de Fischer-Tropsch, i diverses partícules inorgàniques nanomètriques per al seu ús en membranes de matriu mixta. Referent a la fabricació de les membranes, la tesi aborda principalment dos tipus: orgàniques i inorgàniques. Respecte a les membranes orgàniques, diferents materials polimèrics s'ha considerat com a candidats prometedors, tant per a la capa selectiva de la membrana, així com com a suport d'aquesta. S'ha treballat amb poliimides, ja que són materials amb temperatures de transició vítria molt alta, per al seu posterior ús en reaccions industrials que tenen lloc entre 250-300 °C. Per a aconseguir membranes molt permeables, mantenint una bona selectivitat, és necessari obtindre capes selectives de menys d'una micra. Emprant com a material de suport altre tipus de polímer, no és necessari estudiar la compatibilitat entre ells, sent menys complexa l'obtenció de capes fines. En canvi, si el suport és de tipus inorgànic, un exhaustiu estudi de la relació entre la concentració i la viscositat de la solució polimèrica és altament necessari. Diverses partícules inorgàniques nanomètriques es van estudiar per a afavorir la permeació d'aigua a través dels materials polimèrics. En segon lloc, quant a membranes inorgàniques, es va realitzar la funcionalització d'una membrana de pal¿ladi per a afavorir la permeació d'hidrogen i evitar la contaminació per monòxid de carboni. El motiu pel qual es va dopar amb un altre metall la capa selectiva de la membrana metàl¿lica va ser per a poder emprar-la en un reactor de Fischer-Tropsch. En relació amb el disseny i fabricació dels reactors, durant aquesta tesi, es va desenvolupar el prototip d'un microreactor per a la metanació de CO2, on una membrana polimèrica de capa fina selectiva a l'aigua es va integrar per a així evitar la desactivació del catalitzador i al seu torn desplaçar l'equilibri i augmentar la conversió de CO2. D'altra banda, un reactor de Fischer-Tropsch va ser redissenyat per a poder introduir una membrana metàl¿lica selectiva a l'hidrogen i poder injectar-lo de manera controlada. D'aquesta manera, i seguint estudis previs, el objectiu va ser millorar la selectivitat als productes desitjats mitjançant el hidrocraqueix i la hidroisomerització d'olefines i parafines amb l'ajuda de l'alta pressió parcial d'hidrogen.
[EN] The present thesis is focused on the development of new gas-separation membranes, as well as their in-situ integration on catalytic membrane reactors for process intensification. For this purpose, several materials have been synthesized such as polymers for membrane manufacture, catalysts for CO2 methanation and Fischer-Tropsch synthesis reaction, and inorganic materials in form of nanometer-sized particles for their use in mixed matrix membranes. Regarding membranes manufacture, this thesis deals mainly with two types: organic and inorganic. With regards to the organic membranes, different polymeric materials have been considered as promising candidates, both for the selective layer of the membrane, as well as a support thereof. Polyimides have been selected since they are materials with very high glass transition temperatures, in order to be used in industrial reactions which take place at temperatures around 250-300 ºC. To obtain highly permeable membranes, while maintaining a good selectivity, it is necessary to develop selective layers of less than one micron. Using another type of polymer as support material, it is not necessary to study the compatibility between membrane and support. On the other hand, if the support is inorganic, an exhaustive study of the relation between the concentration and the viscosity of the polymer solution is highly necessary. In addition, various inorganic particles were studied to favor the permeation of water through polymeric materials. Secondly, as regards to inorganic membranes, the functionalization of a palladium membrane to favor the permeation of hydrogen and avoid carbon monoxide contamination was carried out. The membrane selective layer was doped with another metal in order to be used in a Fischer-Tropsch reactor. Regarding the design and manufacture of the reactors used during this thesis, a prototype of a microreactor for CO2 methanation was carried out, where a thin-film polymer membrane selective to water was integrated to avoid the deactivation of the catalyst and to displace the equilibrium and increase the CO2 conversion. On the other hand, a Fischer-Tropsch reactor was redesigned to introduce a hydrogen-selective metal membrane and to be able to inject it in a controlled manner. In this way, and following previous studies, the aim is to enhance the selectivity to the target products by hydrocracking and hydroisomerization the olefins and paraffins assisted by the presence of an elevated partial pressure of hydrogen.
I would like to acknowledge the Spanish Government, for funding my research with the Severo Ochoa scholarship.
Escorihuela Roca, S. (2019). Novel gas-separation membranes for intensified catalytic reactors [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/121139
TESIS

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

Dans cette étude de doctorat, la technique de dépôt tridimensionnel de fibres (3DFD) a été appliquée pour développer et fabriquer des structures de support catalytique multi-canaux avancées. En utilisant cette technique, le matériau, la porosité, la forme et la taille des canaux et l'épaisseur des fibres peuvent être contrôlées. L'objectif de cette recherche est d'étudier les performances des supports structurés 3D conçus pour la méthanation du CO2 en termes d'activité, de sélectivité de stabilité et d’étudier l'impact des propriétés spécifiques introduites dans la conception structurale des supports
In this doctoral study, the three dimensional fibre deposition (3DFD) technique has been applied to develop and manufacture advanced multi-channelled catalytic support structures. By using this technique, the material, the porosity, the shape and size of the channels and the thickness of the fibres can be controlled. The aim of this research is to investigate the possible benefits of 3D-designed structured supports for CO2 methanation in terms of activity, selectivity and stability and the impact of specific properties introduced in the structural design of the supports

Cette étude concerne la valorisation du dioxyde de carbone par le procédé de méthanation. Elle vise à mettre au point des catalyseurs efficaces pour cette réaction. L'espèce active est le nickel métallique. Différents supports ont été étudiés tels que SiO₂, Al₂O₃, MgO, Y₂O₃ et CeO₂. Ces catalyseurs ont été préparés par la méthode d'imprégnation à sec. Dans un premier temps, les différents catalyseurs ont été caractérisés par différentes techniques physico-chimiques dont la Diffraction des Rayons X (DRX), la Réduction en Température Programmée (RTP-H₂), la Désorption en Température Programmée (DTP-CO₂), l'Adsorption d'Azote (méthode BET) et la Chimisorption d'Hydrogène. Dans un deuxième temps, les différents catalyseurs ainsi préparés ont été testés dans la réaction de méthanation du CO₂. Le catalyseur Ni/CeO₂ présente les meilleures performances catalytiques, parmi les systèmes étudiés. L'ajout du ruthénium améliore l'activité catalytique et la stabilité des catalyseurs. Le catalyseur Ru(0,5%)-Ni(5%)/CeO₂ est le plus performant, il présente une bonne activité catalytique et une bonne stabilité même pour une pression de 10 bar. Ceci le rend plus avantageux pour une application industrielle
This study concerns the valorization of carbon dioxide by the methanation process. It aims to develop effectiv catalysts for this reaction. The active species is metallic nickel. Different supports have been studied such as SiO₂, Al₂O₃, MgO, Y₂O₃ and CeO₂. These catalysts were prepared by the dry impregnation method. Initially, the different catalysts were characterized by different physicochemical techniques including X-ray Diffraction (XRD), Temperature Programmed Reduction (TPR-H₂), Temperature Programmed Desorption (TPD-CO₂), nitrogen adsorption (BET method) and hydrogen chemisorption. In a second step, the various catalysts thus prepared were tested in the CO₂ methanation reaction. The Ni/CeO₂ catalysts has the best catalytic performance, among the systems studied. The addition of ruthenium improves the catalytic activity and the stability of the catalysts. The catalyst Ru(0.5%)-Ni(5%)/CeO₂ is the most efficient, it has good catalytic activity and good stability even as a pressure of 10 bar. This makes it advantageous for an industrial application

Le reformage à sec du méthane (DRM) est un processus qui convertit simultanément CH4 et CO2 en un mélange gazeux de H2 et de CO appelé syngas. Les catalyseurs à base de Ni sont particulièrement prometteurs mais ils ne sont pas stables en raison du frittage du Ni et du dépôt de coke. Dans cette thèse, nous avons développé deux voies de synthèse de catalyseurs mésoporeux à base de Ni-Al2O3 dans lesquels Ni est stabilisé dans l'oxyde, ce qui donne une activité et une stabilité élevées en DRM. Des techniques physicochimiques complémentaires ont été appliquées pour identifier les propriétés des matériaux à toutes les étapes de préparation et d'activation. La première approche comprend la synthèse « EISA one-pot » de matériaux mésoporeux Ni-Mg-Al2O3. L’échantillon à base de 15% en poids de Mg (charge optimale) contribue à une dispersion élevée et homogène de Ni et de Mg tout en préservant la qualité structurale de la matrice Al2O3 mésoporeuse. La basicité accrue renforce l'activité et la stabilité. La seconde méthode consiste à synthétiser des matériaux mésoporeux Ni-Al2O3 innovants en utilisant une structure organométallique (MOF) comme matrice sacrificielle. Cette procédure permet la formation de petites nanoparticules de Ni stabilisées de manière homogène dans le support de grande surface spécifique, insensibles au frittage et à la formation de nanotubes de carbone lors de la réaction de DRM. Les tests catalytiques complétés par des calculs thermodynamiques montrent l’efficacité des matériaux synthétisés non seulement pour le reformage à sec du méthane, mais également pour la méthanation du CO2 et le reformage à sec de biogaz issu de pyrolyse
Dry reforming of methane (DRM) is a process that converts CH4 and CO2 gases into syngas, a gaseous mixture of H2 and CO. Ni based catalysts proved to be suitable for the reaction due to their good activity, wider availability and lower cost than noble-based materials. However, these catalysts are not stable due to Ni sintering and coke deposition. In this thesis we developed two different synthesis routes of mesoporous Ni-Al2O3 based catalysts that can occlude Ni inside the pores achieving high activity and stability in DRM. A set of complimentary physicochemical techniques was systematically applied to thoroughly investigate the materials properties at all steps of preparation and activation. The first approach embraces synthesis of mesoporous Ni-Mg-Al2O3 materials by one-pot EISA strategy. Results demonstrate that 15 wt% Mg (optimum loading) based sample contribute to high and homogenous dispersion of both Ni and Mg, preserving ordered mesoporous Al2O3 walls. The good structural and textural characteristics in addition to the enhanced basicity reinforce activity and stability. The second method involves synthesizing new mesoporous Ni-Al2O3 materials using metal-organic framework as sacrificial template. This procedure results in small Ni nanoparticles homogeneously dispersed and stabilized within the high surface area support resisting sintering and inhibiting carbon nanotubes formation during reforming reaction. Based on catalytic tests completed by thermodynamics calculations, the synthesized materials proved to be eficient not only for dry reforming of methane, but also for CO2 methanation reaction and dry reforming of waste pyrolysis products

Ce travail s'inscrit dans le cadre Power-to-Gas, dont l'objectif est de stocker les surplus d'énergie électrique issus de sources renouvelables sous forme d'énergie chimique, en l'occurrence le méthane. L'intermittence de la production électrique requiert une certaine flexibilité du système de méthanation par rapport aux variations temporelles de conditions opératoires. Dans ce contexte, les travaux effectués au cours de cette thèse sont dédiés à l'étude du comportement dynamique d'un réacteur-échangeur de méthanation à lit fixe catalytique. Une maquette de réacteur finement instrumentée en thermocouples est conçue et permet l'étude expérimentale des performances du réacteur et de son comportement thermique en régime dynamique. En particulier, des phénomènes de fronts d'onde thermique, de dépassements et de réponses inverses sont retrouvés. Les paramètres hydrodynamiques et thermiques du lit ont été caractérisés expérimentalement. Une modélisation de la maquette de réacteur-échangeur est également établie et permet de simuler son fonctionnement. Les résultats expérimentaux sont comparés aux résultats de simulation, permettant l'analyse précise des comportements observés dans le réacteur
This work is within the Power-to-Gas framework, which aims to store the electrical energy surpluses from renewable energy in chemicals, here the methane. The intermittency of the electrical production requires the methanation system to have a certain level of flexibility with respect to temporal changes of operational conditions. In this context, the work carried out during this thesis is dedicated to the study of the dynamic behavior of a catalytic fixed-bed heat-exchanger methanation reactor. A reactor-exchanger highly equipped with thermocouples is designed and is used for the experimental study of the performances and the dynamics behavior of such a reactor. In particular, phenomena of thermal wave fronts, overshoot and inverse responses are found. The hydrodynamic and thermal parameters of the bed have been experimentally characterized. Modeling of the reactor-exchanger is also established and simulations of the reactor behavior are done. The experimental results are compared with the simulation results, allowing the precise analysis of the behaviors observed in the reactor

thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016.
Selective CO methanation (SMET), as an alternative process for cleaning trace CO in reformate gas feed for fuel cell applications, has gained increasing attention recently. This is mostly due to the fact that the technique can circumvent the major setbacks experienced in the preferential oxidation (PROX) reaction of CO to CO2. The PROX technique is a more established process and has been extensively researched over the years. In this project, we have focused on studying Ru supported on carbon and titania based materials for the selective CO methanation reaction. A rutile morphology in the form of a novel dandelion like structure was synthesized using TiCl4. The rutile dandelion like structure was composed on rutile nanorods which were radially arranged and they had fairly high surface area (61 m2g-1). Titania rutile was also synthesized by calcining anatase at 900 ℃ for 10 h. It was observed that the rutile grains had grown larger after the transformation from anatase to rutile and this was accompanied by a collapsed surface area (from 52 to 9 m2/g). The two rutile morphologies were employed as Ru catalyst supports and applied in both CO and selective CO methanation reactions. The dandelion like supported catalyst demonstrated higher catalytic performance compared to the thermally prepared rutile supports. This was attributed to the smaller Ru particles sizes which were found to be sinter resistant. Small RuO2 nanoparticle sizes supported on carbon nanotubes (CNTs) were obtained by the use of a microwave polyol synthesis. Tuning the microwave temperature generated the different RuO2 sizes without changing the percentage loading or conventionally heat treating the catalyst. The CNTs were synthesized by a chemical vapour deposition (CVD) method using a Fe-Co/CaCO3 catalyst. The microwave polyol synthesized catalysts were compared to a wet impregnated catalyst. It was noted that the impregnated catalyst preparation method showed little control over the RuO2 particle size distribution. The catalysts were tested in both selective CO and CO methanation. The catalyst with smaller particle sizes, prepared using a short microwave induction time, performed better when compared to the other catalysts. It was also observed that all the catalysts promoted the undesired reverse water gas shift reaction for all the catalyst at temperatures above 260 ℃. Abstract The surface of the CNTs were altered by introducing pyridinic nitrogen in an in situ doping process to give nitrogen doped CNTs (N-CNTs). The doping was confirmed by TEM as the CNTs were seen to show bamboo compartments in the tubular CNT structure. A composite of CNT-TiO2 was prepared by a facile hydrothermal process and used to modify the CNTs. The TiO2 (anatase) coated CNTs were synthesized using titanium butoxide as anatase source. A solution containing CNTs and the TiO2 source was reacted in an autoclave. Images from TEM and SEM revealed partially coated anatase N-CNTs and CNTs. Both the doping and the coating of the CNTs resulted in an improved surface area. The coated samples showed significantly improved thermal stability which was attributed to the shielding effect of the TiO2. Raman analysis revealed that the N-CNTs had a high defect content compared to the CNTs. When these materials were employed as Ru catalyst supports for methanation reactions, the nitrogen doped CNTs demonstrated superior catalytic activity compared to the CNT supported catalyst. They both promoted the reverse water gas shift reactions. The NCNT-TiO2 and CNT-TiO2 catalysts showed higher activity and significantly retarded the reverse water gas shift reaction. Mesoporous solid carbon spheres (CSs-H) synthesized via the hydrothermal route using sugar as carbon source was functionalized by acid treatment. The data were compared to an un-functionalized CSs-H used as a Ru catalyst support. Raman data suggested a high defect content for the functionalized spheres and the carbons had a slightly higher surface area when compared to the un-functionalized spheres. Two catalysts were prepared from the functionalized solid carbon spheres; a microwave irradiation prepared catalyst and a wet impregnation prepared catalyst. The microwave prepared catalyst, with slightly smaller Ru particles, performed slightly better in both CO and selective CO methanation reactions than the impregnated catalyst. In the CO2 only methanation reaction almost similar activity was obtained for both catalysts which implied the preparation method did not have much effect on the reaction. The un-functionalized supported catalyst performed poorly in both the reactions due to the poorly dispersed Ru nanoparticles which had sintered. Despite the poor performance, the catalyst did not promote the undesired RWGS reaction. This was attributed to the absence of oxygenated functional groups such as OH.
LG2017

碩士
國立交通大學
應用化學系碩博士班
99
The synergetic effect between Ni and V2O3 in carbon dioxide methanation was investigated using compositions, different loading, reaction temperature, amount of catalysts and synthetic routes. The catalysts were characterized by powder X-ray diffraction (PXRD), inductively coupled plasma-atomic emission spectrometer (ICP-AES), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). Formation of Ni–V–O solid solution was confirmed by XPS and TPR studies. The optimal Ni/(Ni + V2O3) molar percent for the highest methane yield is found to be 40. The conversion of carbon dioxide to methane was increased as the amount of loading catalysts increased. Catalysts with Ni/(Ni + V2O3) molar percent of 40 were synthesized by sol-gel, hydrothermal and impregnation methods to study their catalytic activity for carbon dioxide methanation. The results indicate that catalyst prepared by sol-gel method exhibits better performance compared with other methods due to its well-dispersed particles that optimized the amount of triple phase boundaries (TPB) between gas phase and the catalyst. The catalyst with Ni/(Ni + V2O3) molar percent of 40 showed the best activity among other catalysts with the carbon dioxide conversion ~93(1) %, the selectivity of methane ~100(1) % at 400ºC, and very stable catalytic activity for 55 hours.

The accumulation of CO₂ emissions in the atmosphere due to industrialization is being held responsible for climate change with increasing certainty by the scientific community. In order to prevent its further accumulation, CO2 must be captured for storage or conversion to useful products. Current materials and processes for CO₂ capture rely on the toxic and corrosive methylethanolamine (MEA) absorbents and are energy intensive due to the large amount of heat that needs to be supplied to release CO₂ from these absorbents. CO₂ storage technologies suffer from a lack of infrastructure for transporting CO₂ from many point sources to the storage sites as well as the need to monitor CO₂ against the risk of leakage in most cases. Conversion of CO₂ to useful products can offer a way of recycling carbon within the industries that produce it, thus creating processes approaching carbon neutrality. This is particularly useful for mitigation of emissions if CO₂ is converted to fuels, which are the major sources of emissions through combustion. This thesis aims to address the issues related to carbon capture and storage (CCS) by coupling a CO₂ conversion process with a CO₂ capture process to design a system that has a more favorable energy balance than existing technologies. This thesis presents a feasibility study of dual function materials (DFM), which capture CO₂ from an emission source and at the same temperature (320°C) in the same reactor convert it to synthetic natural gas (SNG), requiring no additional heat input. The conversion of CO₂ to SNG is accomplished by supplying hydrogen, which in a real application will be supplied from excess renewable energy (solar and/or wind). The DFM consists of Ru as methanation catalyst and nano dispersed CaO as CO₂ adsorbent, both supported on a porous γ-Al₂O₃ carrier. A spillover process drives CO₂ from the sorbent to the Ru sites where methanation occurs using stored H₂ from excess renewable power. This approach utilizes flue gas sensible heat and eliminates the current energy intensive and corrosive capture (amine solutions) and storage processes without having to transport captured CO₂ or add external heat. The catalytic component (Ru/γ-Al₂O₃) has been investigated in terms of its suitability for a DFM process. Process conditions for methanation have been optimized. It has been observed that the equilibrium product distribution for CO₂ methanation with a H₂:CO₂ ratio of 4:1 can be attained at a temperature of 280°C with a space velocity of 4720 h⁻¹. TGA-DSC has been employed to observe the sequential adsorption and reaction of CO₂ and H₂ over Ru/γ-Al₂O₃. It was shown that H₂ only reacts with a CO₂-saturated Ru/γ-Al₂O₃ surface but does not adsorb on the bare Ru surface at 260°C, consistent with an Eley-Rideal type reaction. In this rate model CO2 adsorbs strongly on the catalyst surface and reacts with gas phase H₂. Kinetic tests were employed to confirm this observation and demonstrated that the rate dependence on CO₂ and H₂ was also consistent with an Eley-Rideal mechanism. A rate expression according to the Eley-Rideal model at 230°C was developed. Activation energy, pre-exponential factor and reaction orders with respect to CO₂, H₂, and products CH₄, and H₂O were determined in order to develop an empirical rate equation in a range of commercial significance. Methane was the only hydrocarbon product observed during CO₂ hydrogenation. The activation energy was found to be 66.084 kJ/g-mole CH₄. The empirical reaction order for H₂ was 0.88 and for CO₂ 0.34. Product reaction orders were essentially zero.

碩士
國立交通大學
應用化學系碩博士班
100
NiO/BaMO3 (M=Ti, Zr, Hf) catalysts were successfully prepared via sol-gel, impregnation, and hydrothermal methods. All catalysts were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), inductively coupled plasma-atomic emission spectrometer (ICP-AES), and specific surface areas (SSA). CO2 methanation performance of each catalyst was examined by changing many factors, such as different compositions, varied Ni loading and several reaction temperatures. The catalysts prepared via impregnation method showed better performance than the others. It revealed the highest value of CO2 conversion and CH4 selectivity at 350?aC. When the reaction temperature rose above 350?aC, the reactivity started to decline. This phenomenon was due to the thermodynamic limitation since CO2 methanation is a slightly exothermic reaction. Among all catalysts, the best performance was achieved by 20 mol% Ni/BaZrO3 with 86.8% CO2 conversion and 99.9% CH4 selectivity at 350?aC. The stability of this optimum catalyst was tested for 64 hours and showed no deactivation. It revealed that CO2 conversion maintained at 86% and the CH4 selectivity was around 99%.

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.

Renewable Natural Gas (RNG) is a low-carbon fuel source that is derived from the anaerobic digestion (AD) or thermal gasification (TG) of biomass, or produced using renewable electricity through the methanation of carbon dioxide. This thesis uses a thermodynamic balance to determine the total technical potential of RNG in the United States, as well as the future technical potential of methanation-derived RNG based on growth curves for renewable electricity. Furthermore, this work establishes an analytic decision-making framework for determining on a rolling basis, from an economic standpoint, whether to sell electricity directly to the grid, or produce and sell methanation-derived RNG. This framework is used to establish the economic potential of RNG, based on Texas wind resources. This work details the formulation of a model that determines which production option generates more marginal profit, based on fluctuating electricity and gas prices. The model also aggregates the total amount of electricity and RNG sold, assuming that the main objective is to maximize the marginal profit of integrated wind- and methanation facilities. This work concludes that the annual technical potential of methanation-derived RNG nationally was 1.03 Quads in 2011. The technical potential of biomass-derived RNG was 9.5 Quads. Thus, the total 2011 technical potential of RNG in the United States was 10.5 Quads, or equal to roughly 43% of the total US consumption of natural gas that year. Assuming a constant, 80% electrolyser efficiency, the technical potential of methanation-derived RNG is expected to rise at an average rate of 1.4% per year, following growth curves for renewable power, until the year 2040, when it will be 1.54 Quads. The 2011 economic potential of methanation-derived RNG in Texas was between 2.06×10⁷ MMBTU and 3.19×10⁷ MMBTU, or between 19.4% and 30.1% of the corresponding annual technical potential. Furthermore, the total marginal profit increase from introducing the option of producing and selling methanation-derived RNG was around $366 million, given a ‘best case scenario’ for the state of Texas.
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