Modelación cinética de la hidrogenación de CO2 para producir metano o metanol.
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Date
2025
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Publisher
Universidad de Concepción
Abstract
La hidrogenación de CO representa una vía prometedora para convertir el CO2 en productos químicos de alto valor agregado mediante procesos catalíticos, donde es necesario el conocimiento de las rutas de reacción que permita un diseño racional de catalizadores. Este trabajo aborda la modelación cinética de la hidrogenación de CO> para la producción de metano y metanol.
Se emplearon catalizadores de 0.5% y 10% peso Ni soportados en SiO2 y ZrO> para la metanación de CO y catalizadores con 6 y 8 átomos de In por nm? soportados en SiO; y ZrO», respectivamente, evaluando sus desempeños en reacciones de hidrogenación de COa, para producir metanol. Los experimentos se llevaron a cabo en un reactor de lecho fijo con condiciones controladas de temperatura, presión y tiempos de residencia, bajo estricto régimen cinético.
Para cada sistema catalítico, se evaluó el efecto del tiempo de residencia evidenciando que los productos (H20 y CO) afectan la cinética y la cobertura de especies en la superficie catalítica, lo que debe ser considerada en el análisis y la modelación. Adicionalmente, se estudió el efecto de las presiones parciales de los reactivos y productos sobre la velocidad de reacción, permitió el entendimiento de la cinética y mecanismo de reacción. Las velocidades de formación de CHa y CH3OH mostraron dependencias positivas con las presiones de H2 y CO2, mientras que las presiones de los productos como agua y/o CO impactaron negativamente.
La ruta de formación de metano sobre Ni involucra la formación de CO* como intermediario, siendo la adición de H* su etapa cinéticamente relevante. El catalizador de Ni soportado en ZrO2 evidenció al formiato bidentado como especie espectadora abundante en superficie, la cual se debe considerar en el balance de sitios del modelo cinético del tipo L-H. Para la reacción de hidrogenación de CO> a metanol se propone que sigue la ruta que involucra la formación de formiatos monodentado cuando el In20; se soporta en SiO», mientras que sobre ZrO> se confirmó la presencia de formiato bidentado. Por su parte, se confirmó que el paso limitante del mecanismo sobre In203/SiO; es la descomposición formiato bidentado, mientras que sobre ZrO» es la tercera adición de H*.
El ajuste de la data cinética para la metanación de CO considerando tanto reactor integral como diferencial entrego valores similares para los parámetros de los modelos cinéticos. Sin embargo, para la formación de metanol, donde se evidenció un efecto pronunciado del agua sobre la cinética, se pudo apreciar una mejora en el ajuste de los datos y un cambio en los parámetros cinéticos al modelar el reactor como flujo-pistón, indicando la necesidad de utilizar dicho modelo en caso de inhibiciones relevantes por los productos.
The hydrogenation of CO> represents a promising pathway to convert CO> into high-value-added chemicals through catalytic processes, where understanding reaction pathways is essential for the rational design of catalysts. This study addresses the kinetic modeling of CO> hydrogenation to produce methane and methanol. Catalysts containing 0.5 wt% and 10 wt% Ni supported on SiOz and ZrO2 were used for CO methanation, while catalysts with 6 and 8 In atoms per nm2 supported on SiO and ZrO», respectively, were evaluated for CO> hydrogenation to methanol. The experiments were conducted in a fixed-bed reactor under controlled conditions of temperature, pressure, and residence time, ensuring a strict kinetic regime. For each catalytic system, the effect of residence time was evaluated, revealing that products (H20 and CO) influence the kinetics and surface species coverage on the catalyst, which must be considered in on both analysis and modeling. Additionally, the effect of the partial pressures of reactants and products the reaction rate was studied, providing insights into the reaction kinetics and mechanism. The formation rates of CH4 and CH;OH showed positive dependencies on Hz and CO pressures, while product pressures, such as water and/or CO, had a negative impact. The methane formation pathway on Ni involves the formation of CO* as an intermediate, with H* addition being the kinetically relevant step. The Ni catalyst supported on ZrO2 exhibited bidentate formate as an abundant spectator species on the surface, which must be considered in the site balance of the L-H type kinetic model. For CO hydrogenation to methanol, the proposed pathway involves the formation of monodentate formates when In20s is supported on SiO>, whereas on ZrO», the presence of bidentate formate was confirmed. Furthermore, the rate-limiting step for the mechanism on In:0;/SiO: was identified as bidentate formate decomposition, while on ZrO», it was the third H* addition. The kinetic data fitting for CO> methanation, considering both integral and differential reactor models, yielded similar values for the kinetic model parameters. However, for methanol formation, Where a pronounced effect of water on kinetics was observed, an improvement in data fitting and a change in kinetic parameters were noted when modeling the reactor as a plug-flow system. This indicates the necessity of using this model in cases where significant product inhibition occurs.
The hydrogenation of CO> represents a promising pathway to convert CO> into high-value-added chemicals through catalytic processes, where understanding reaction pathways is essential for the rational design of catalysts. This study addresses the kinetic modeling of CO> hydrogenation to produce methane and methanol. Catalysts containing 0.5 wt% and 10 wt% Ni supported on SiOz and ZrO2 were used for CO methanation, while catalysts with 6 and 8 In atoms per nm2 supported on SiO and ZrO», respectively, were evaluated for CO> hydrogenation to methanol. The experiments were conducted in a fixed-bed reactor under controlled conditions of temperature, pressure, and residence time, ensuring a strict kinetic regime. For each catalytic system, the effect of residence time was evaluated, revealing that products (H20 and CO) influence the kinetics and surface species coverage on the catalyst, which must be considered in on both analysis and modeling. Additionally, the effect of the partial pressures of reactants and products the reaction rate was studied, providing insights into the reaction kinetics and mechanism. The formation rates of CH4 and CH;OH showed positive dependencies on Hz and CO pressures, while product pressures, such as water and/or CO, had a negative impact. The methane formation pathway on Ni involves the formation of CO* as an intermediate, with H* addition being the kinetically relevant step. The Ni catalyst supported on ZrO2 exhibited bidentate formate as an abundant spectator species on the surface, which must be considered in the site balance of the L-H type kinetic model. For CO hydrogenation to methanol, the proposed pathway involves the formation of monodentate formates when In20s is supported on SiO>, whereas on ZrO», the presence of bidentate formate was confirmed. Furthermore, the rate-limiting step for the mechanism on In:0;/SiO: was identified as bidentate formate decomposition, while on ZrO», it was the third H* addition. The kinetic data fitting for CO> methanation, considering both integral and differential reactor models, yielded similar values for the kinetic model parameters. However, for methanol formation, Where a pronounced effect of water on kinetics was observed, an improvement in data fitting and a change in kinetic parameters were noted when modeling the reactor as a plug-flow system. This indicates the necessity of using this model in cases where significant product inhibition occurs.
Description
Tesis presentada para optar al título de Ingeniero/a Civil Químico/a.
Keywords
Hidrogenación, Metano, Metanol