Estudio cinético de la hidrogenación de 9-etilcarbazol para el almacenamiento de H2 sobre catalizadores de Ru.
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Date
2025
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Universidad de Concepción
Abstract
Los combustibles fósiles, aunque predominantes en la generación de energía, poseen un fuerte impacto ambiental, motivando la búsqueda de otras fuentes energéticas más limpias y sostenibles. Bajo este contexto, el hidrógeno emerge como un candidato ideal para el transporte energético, pues posee una alta eficiencia energética, tiene una alta disponibilidad y baja toxicidad ambiental. Sin embargo, los actuales desafíos relacionados con su almacenamiento generan un gran impedimento para su masificación y uso a gran escala.
Una solución prometedora son los líquidos orgánicos portadores de hidrógeno (LOHCs, por sus siglas en inglés) los cuales son seguros, fáciles de transportar y poseen una alta densidad energética. El 9 etilcarbazol (9EC) emerge como un candidato bastante atractivo, pues es capaz de almacenar hasta un 5,7wt% de hidrógeno, por lo que su estudio nos permite enfrentar los desafíos técnicos de las hidrogenaciones, las cuales requieren condiciones específicas y son favorecidas por catalizadores de metales nobles como el platino, el paladio y el rutenio.
El objetivo de este trabajo fue realizar un estudio cinético de la hidrogenación de 9EC sobre un catalizador de 5wt% Ru/Al2O3. El catalizador fue sintetizado mediante impregnación húmeda, teniendo un área superficial específica de 209 m2/g, una dispersión del 11,6% de sus nanopartículas de rutenio y una reducción total a los 523 K.
El modelo cinético de ley de potencias obtenido mediante regresión lineal posee errores bajo el 4% y ordenes de reacción aparente entre 0,3 y 0,7 con respecto al 9EC y de orden 0,11 con respecto al hidrógeno. Para los modelos cinéticos Langmuir-Hinshelwood (L-H), se siguió la teoría postulada por Vannice y Chorkendorff, donde las aproximaciones de cuasi-equilibrio, MARI y estado estacionario fueron usadas. Para el diseño del reactor se supuso que el reactor es isotérmico, propiedades físicas constantes y sin limitaciones de transporte, lo cual fue demostrado. El primer modelo L-H se realizó sin considerar productos tuvo errores entre un 7% y un 47% teniendo consistencia física con respecto al H2 cumpliendo con los tres criterios de Vannice, sin embargo, el ajuste gráfico no es representativo pues no presenta inhibición por productos. El segundo modelo L-H se realizó considerando que todos los productos son equivalentes al tetrahidro-9-etilcarbazol, donde se obtuvieron errores entre un 7% y un 19%. Siendo matemáticamente más exacto y presentando inhibición por productos, la entropía de adsorción del 9EC12H resulta ser positiva, por lo que el modelo es descartado requiriendo un mayor análisis.
Fossil fuels, although predominant in energy generation, have a significant environmental impact that prompts the search for cleaner and more sustainable energy sources. Based on this context, hydrogen emerges as an ideal candidate for energy transport due to its high energy efficiency and low environmental toxicity. However, current challenges related to its storage pose a significant barrier for a mass adoption scenario. A promising solution lies in liquid organic hydrogen carriers (LOHCs), which are safe, easy to transport and have high energy density. Among these, 9-ethylcarbazole (9EC) stands out as a particularly attractive candidate, capable of storing up to 5.7 wt% of hydrogen. Its study allows us to address the technical challenges of hydrogenation, a catalytic reaction favored by noble metals like Platinum, Palladium and Ruthenium that require specific operation conditions. The objective of this work was to conduct a kinetic study of the hydrogenation of 9EC using a 5 wt% Ru/Al₂O₃ catalyst. The catalyst was synthesized via wet impregnation, exhibiting a specific surface area of 209 m²/g, possess an 11.6% dispersion of ruthenium nanoparticles, and reduces completely at 523 K. The power-law kinetic model, obtained through linear regression, exhibited errors below 4%, with apparent reaction orders between 0.3 and 0.7 for 9EC and 0.11 for hydrogen. For the Langmuir Hinshelwood (L-H) kinetic models, the theory proposed by Vannice and Chorkendorff was followed, employing quasi-equilibrium, MARI, and steady-state approximations. Reactor design assumed an isothermal reactor with constant physical properties and no transport limitations, which was demonstrated during this work. The first L-H model, developed without considering products, exhibited errors ranging from 7% to 47%. While it showed physical consistency with respect to H₂ and met Vannice’s criterias, its graphical fit was not representative as it did not account for product inhibition. The second L-H model assumed that all products were equivalent to tetrahydro-9-ethylcarbazole, yielding errors between 7% and 19%. Although being more accurate and incorporating product inhibition, the positive adsorption entropy of 9EC12H rendered this model invalid, requiring further analysis.
Fossil fuels, although predominant in energy generation, have a significant environmental impact that prompts the search for cleaner and more sustainable energy sources. Based on this context, hydrogen emerges as an ideal candidate for energy transport due to its high energy efficiency and low environmental toxicity. However, current challenges related to its storage pose a significant barrier for a mass adoption scenario. A promising solution lies in liquid organic hydrogen carriers (LOHCs), which are safe, easy to transport and have high energy density. Among these, 9-ethylcarbazole (9EC) stands out as a particularly attractive candidate, capable of storing up to 5.7 wt% of hydrogen. Its study allows us to address the technical challenges of hydrogenation, a catalytic reaction favored by noble metals like Platinum, Palladium and Ruthenium that require specific operation conditions. The objective of this work was to conduct a kinetic study of the hydrogenation of 9EC using a 5 wt% Ru/Al₂O₃ catalyst. The catalyst was synthesized via wet impregnation, exhibiting a specific surface area of 209 m²/g, possess an 11.6% dispersion of ruthenium nanoparticles, and reduces completely at 523 K. The power-law kinetic model, obtained through linear regression, exhibited errors below 4%, with apparent reaction orders between 0.3 and 0.7 for 9EC and 0.11 for hydrogen. For the Langmuir Hinshelwood (L-H) kinetic models, the theory proposed by Vannice and Chorkendorff was followed, employing quasi-equilibrium, MARI, and steady-state approximations. Reactor design assumed an isothermal reactor with constant physical properties and no transport limitations, which was demonstrated during this work. The first L-H model, developed without considering products, exhibited errors ranging from 7% to 47%. While it showed physical consistency with respect to H₂ and met Vannice’s criterias, its graphical fit was not representative as it did not account for product inhibition. The second L-H model assumed that all products were equivalent to tetrahydro-9-ethylcarbazole, yielding errors between 7% and 19%. Although being more accurate and incorporating product inhibition, the positive adsorption entropy of 9EC12H rendered this model invalid, requiring further analysis.
Description
Tesis presentada para optar al título de Ingeniero/a Civil Químico/a.
Keywords
Hidrógeno como combustible, Combustibles Investigaciones, Hidrogenación