BUSCADOR RECOLECTA

Silicone microreactors containing microchannels of 500 μm width in a single or triple stack configuration have been manufactured, coated with an Au/TiO2 photocatalyst and tested for the photocatalytic production of hydrogen from water-ethanol gaseous mixtures under UV irradiation. Computational fluid dynamics (CFD) simulations have revealed that the design of the distributing headers allowed for a homogeneous distribution of the gaseous stream within the channels of the microreactors. A rate equation for the photocatalytic reaction has been developed from the experimental results obtained with the single stack operated under different ethanol partial pressures, light irradiation intensities and contact times. The hydrogen photoproduction rate has been expressed in terms of a Langmuir-Hinshelwood-type equation that accurately describes the process considering that hydrogen is produced through the dehydrogenation of ethanol to acetaldehyde. This equation incorporates an apparent rate constant (kapp) that has been found to be proportional to the intrinsic kinetic rate constant (k), and that depends on the light intensity (I) as follows: kapp = k·I0.65. A three-dimensional isothermal CFD model has been developed in which the previously obtained kinetic equation has been implemented. The model adequately describes the production of hydrogen of both the single and triple stacks. Moreover, the specific hydrogen productions (i.e. per gram of catalyst) are very close for both stacks thus suggesting that the scaling-up of the process could be accomplished by simply numbering-up. However, small deviations between the experimental and predicted hydrogen production suggest that a fraction of the radiation is absorbed by the microreactor components which should be taken into account for scaling-up purposes., This work has been funded through MINECO grants and FEDER funding ENE2015-63969-R and ENE2015-66975-C3-1-R. JL is Serra Húnter Fellow and is grateful to ICREA Academia program. AC is grateful to MINECO for PhD grant BES-2013-065709. LS is grateful to Generalitat de Catalunya for a Beatriu de Pinós grant (2013 BP-B 00007).

Los procesos Gas-to-Liquid (GTL), basados en la transformación de gas natural en hidrocarburos sintéticos, son de gran interés para la valorización de los nuevos recursos que emergen actualmente fruto de la aparición de nuevos yacimientos y fuentes de gas natural no convencional (GNNC). La primera etapa del proceso GTL consiste en la conversión del CH4 en gas de síntesis, una mezcla de H2, CO y CO2, aunque también puede contener N2. Entre las distintas alternativas para producir gas de síntesis, la oxidación parcial de metano (OPM) resulta ventajosa, ya que se podrían suavizar considerablemente las condiciones de operación de las tecnologías industriales existentes, con el consiguiente ahorro económico y mejoras en seguridad. Con el fin de obtener altos rendimientos a gas de síntesis se requieren altas temperaturas y/o catalizadores adecuados. Así, el diseño del catalizador es clave para obtener una conversión de metano a gas de síntesis exitosa y eficiente.
El objetivo de esta tesis ha sido el de desarrollar catalizadores de Co y Rh para llevar a cabo la reacción de oxidación parcial de metano (OPM) a gas de síntesis; pretendiendo avanzar asimismo en el conocimiento del desarrollo de esta importante reacción por vía catalítica. Para la consecución de este objetivo general, se han abordado diversos objetivos específicos:
- conocer en mayor profundidad cómo se desarrolla la reacción sobre este metal desarrollando un estudio paramétrico de la influencia de las principales variables de operación sobre la conversión de metano, rendimiento a H2 y CO y estabilidad, así como un estudio cinético. En este contexto, entre los resultados más destacables de la tesis cabe destacar que el estudio cinético llevado a cabo ha permitido plantear un modelo cinético para la reacción de OPM, el cual permite describir de manera satisfactoria los resultados experimentales obtenidos y poder modelar adecuadamente el complejo esquema de la reacción global de OPM en base a la combinación de cuatro reacciones elementales sencillas, como son: la combustión de metano, el reformado de metano con vapor de agua, la reacción de desplazamiento del gas de agua reversa (RWGS) y la combustión de hidrógeno.
- investigar el efecto de las condiciones de activación de catalizadores de Co así como del desarrollo de la propia reacción sobre el comportamiento catalítico con el fin de obtener información sobre el papel de la función metálica en el proceso de oxidación parcial.
Para lograr una adecuada evolución de la reacción de OPM hacia la producción estable y prolongada en el tiempo de gas de síntesis resulta esencial mantener el Co en estado metálico durante el transcurso de la reacción y sobre todo en los instantes iniciales, que condicionan notablemente la estabilidad de los catalizadores. Ello delimita la ventana de condiciones de operación para la reacción de OPM catalítica y, concretamente, el intervalo óptimo de temperaturas de reacción, idealmente entre 700 y 800 oC.
- Realizar un amplio estudio exploratorio considerando elementos básicos de la formulación del catalizador: naturaleza del soporte, método de preparación, incorporación de promotores del Co y del soporte, carga de metal, etc. con el fin de establecer las bases que guíen el diseño de un catalizador de Co para OPM. Los resultados obtenidos en los ensayos de actividad catalítica efectuados con un catalizador Co/Mg-Al preparado en el laboratorio por coprecipitación y calcinado a 500 oC se encuentran a la vanguardia del estado del arte en el arriba citado campo de investigación. Estos resultados mejoran ampliamente los existentes hasta el momento, permitiendo alcanzar conversiones de metano y selectividades hacia la producción de gas de síntesis muy próximas a las de los valores dictados por el equilibrio termodinámico de la reacción de OPM a 800 oC de manera estable y prolongada durante tiempos de reacción tan largos como 48 h y a GHSV tan elevadas como 1000 L N/(gcat•h).
- Finalmente, también se ha planteado como objetivo explorar el papel de la OPM en la valorización del biogás mediante reformado para la obtención de gas de síntesis. Estrategias de reformado combinado de tipo “oxy-CO2” pueden constituir una opción interesante para la valorización de este recurso renovable cada vez producido en mayor volumen. En este sentido, el desarrollo de catalizadores de Rh en combinación con la introducción de pequeñas cantidades de oxígeno en la alimentación supone una estrategia exitosa que puede conducir a la viabilidad del proceso a escalas mayores si se logra desarrollar catalizadores de Rh con menores cargas en el catalizador que las utilizadas en esta tesis, esto es, contenidos de Rh inferiores al 0,5 % en masa del catalizador final., Ministerio de Economía y Competitividad (Proyectos ENE2012-37431-C03-03 y ENE2015-66975-C3). Ayuda para Contratos Predoctorales para la Formación de Doctores 2013 (ref. BES-2013-062799)., Programa Oficial de Doctorado en Química Sostenible (RD 1393/2007), Kimika Jasangarriko Doktoretza Programa Ofiziala (ED 1393/2007)

Dry reforming and partial oxidation of biogas were studied using 0.5 wt.% Rh/Al2O3 catalysts, both inhouse prepared and commercial. The effects of O2 addition on syngas yield and biogas conversion were
studied at 700 C using different O2/CH4 ratios in the gas feeding stream: 0 (dry reforming), 0.12, 0.25,
0.45 and 0.50. The highest CH4 conversion, H2 yield and H2/CO molar ratio were obtained with an O2/CH4
ratio of 0.45, even though simultaneous valorization of both CH4 and CO2 could be best attained when the
O2/CH4 ratio was 0.12. Increased biogas conversions and syngas yields were obtained by increasing
reaction temperatures between 650 and 750 C. A detrimental influence on catalytic activity could be
observed when the catalyst was subjected to calcination. Increasing the hold time of the thermal
conditioning of the catalyst under inert flow altered Rh dispersion, though had no significant impact on
catalyst performance in the dry reforming of methane at 700 C and 150 N L CH4/(gcat h). Characterization
of spent samples after reaction by Raman spectroscopy revealed the presence of carbonaceous deposits of
different nature, especially on the commercial(named as Rh com) and calcined (Rh calc) catalysts, though
oxygen addition in the biogas feed significantly reduced the amount of these deposits. The Rh catalysts
that had not been calcined after impregnation (Rh prep) did not present any noticeable characteristic
peaks in the G and D bands. In particular, scanning transmission electron microscopy (STEM) images of
the spent Rh prep sample revealed the presence of very highly dispersed Rh nanoparticles after reaction,
of particle sizes of about 1 nm, and no noticeable C deposits. Combined oxy-CO2 reforming of biogas using
highly dispersed and low metal-loading Rh/Al2O3 catalysts with low O2 dosage in the reactor feed can be
used to effectively transform biogas into syngas., The authors thank the Spanish Ministerio de Economía,
Industria y Competitividad (MINECO) (ENE2015-66975-C3), Spanish Ministerio de Ciencia, Innovación y Universidades (RTI2018-
096294-B-C31), and the European Regional Development Fund
(ERDF/FEDER) for the financial support. MINECO and ERDF/FEDER
are also thanked for the pre-doctoral aid (BES-2016-077866)
awarded to Andrea Navarro and for funding the contract of Dr.
Ainara Moral. The Universidad Pública de Navarra (UPNA) is also
acknowledged for the post-doctoral aid awarded to Inés Reyero.

There is still a need for active, selective and stable heterogeneous catalysts for the synthesis of biodiesel. In this work, magnesium-aluminium hydrotalcites with Mg/Al molar ratios within the 1.5–5 range were synthesized by coprecipitation and used as transesterification catalysts for the synthesis of biodiesel. The mixed oxides obtained after calcination recovered the hydrotalcite structure in the form of meixnerite after rehydration in boiling water. The solids were characterized by XRD, TGA, N2 adsorption-desorption, and SEM. Basic properties were assessed by means of Hammett indicators and CO2-TPD. Rehydrated materials with the highest Mg/Al ratios showed some distinctive features: low surface area, well defined flake-like crystals, high basicity and strong basic sites with H_ values above 11. They were also the most active catalysts allowing to achieve 51–75% sunflower oil methanolysis conversion after 8 h of reaction under mild conditions (60 °C, 1 atm), methanol/oil molar ratio of 12 using between 2 and 6 wt% of catalyst. The conversion increased up to 96% (92% fatty acid methyl esters yield) using 2 wt% catalyst and methanol/oil molar ratio of 48. Catalyst leaching was not a serious problem with these solids that could be reutilized maintaining very good activities. A general accordance between solids basic properties and their catalytic performance has been observed. These results are among the best reported in the literature for heterogeneous methanolysis catalysts and have been attributed to the high basicity of the rehydrated solids and the presence of strong and accessible basic sites probably consisting in interlayer hydroxide anions at the edges of the crystals., The authors thank the Spanish Ministerio de Economía y Competitividad (MINECO), the former Ministerio de Ciencia e Innovación (prj. refs. TRACE, TRA2009_0265 and ENE2015-66975-C3-1-R) and the European Regional Development Fund (ERDF/FEDER) for the financial support. MINECO and FEDER are also acknowledged for the pre-doctoral aid awarded to Ainara Moral (Ref. num. BES-2013-062799) funded under the ENE2015-66975-C3-1-R project (“Structured Catalytic Systems for Biofuels Production”). J.E., O.S. and M.M. acknowledge the Basque Government (IT1069-16) and the Spanish MINECO/FEDER (ENE2015-66975-C3-3-R and CTQ2015-73901-JIN) for the financial support.

Las tecnologías de digestión anaerobia para procesar corrientes residuales (fracción orgánica de resi­duos de vertedero, lodos de estaciones depuradoras de aguas residuales, purines, etc.) han originado un incremento de la producción de biogás. El biogás está compuesto principalmente por metano y dióxido de carbono, aunque contiene otros componentes minoritarios e impurezas que obligan a efectuar tratamientos para su purificación y acondicionamiento. Existen diversas alternativas para el aprovechamiento y la valorización de este gas, como son: su utilización directa en la generación de energía calorífica y/o eléctrica, su conversión a biometano, y la producción de gas de síntesis (H2+­CO), que posteriormente permite producir combustibles líquidos y/o compuestos químicos de interés como el metanol. En este trabajo se presenta una revisión general de las alternativas de valorización de biogás, con énfasis en los procesos de reformado catalítico, tales como el reformado seco o con vapor de agua y procesos de reformado combinado incluyendo la oxidación parcial., The development of anaerobic digestion technologies for processing various residual streams (the organic fraction of landfill wastes, sewage sludge from wastewater treatment plants, pig and cow manure, etc.) has led to an increase in the production of biogas. Biogas is mainly composed of methane and carbon dioxide, though other minor compounds and impurities are present, hence different treatments must be applied for its purification and conditioning. Amidst the va¬rious alternatives for its use and valorization, the most important are the following: direct use in the generation of heat and/or electric power, upgrading to biomethane, and syngas production (H2+CO), which is further used as raw material for producing liquid fuels and/or chemicals such as methanol. This work presents an overview on the different alternatives for biogas valorization, with special emphasis on catalytic reforming processes, such as dry and steam reforming, together with combined reforming routes including partial oxidation., Este trabajo ha sido financiado por el Ministerio de Economía y Competitividad de España (MINECO, proyecto ENE2015-66975-C3-1-R) y por el Fondo Europeo de Desarrollo Regional (FEDER), así como por las ayudas pre-doctorales para la Formación de Personal Investigador concedidas a Andrea Navarro (BES-2016-077866) y a Ainara Moral (BES-2013-062799)

Abnormal combustion phenomena are among the main hurdles for the introduction of hydrogen in the transportation sector through the use of internal combustion engines (ICEs). For that reason the challenge is to guarantee operation free from combustion anomalies at conditions close to the ones giving the best engine output (maximum brake torque and power). To this end, an early and accurate detection of abnormal combustion events is decisive in order to allow the electronic control unit deciding suitable correcting actions. In this work, an automotive size 4-cylinder 1.4 L naturally aspirated port-fuel injection spark ignition Volkswagen engine adapted to run on hydrogen has been investigated. Three distinct methods (in-cylinder pressure, block-engine vibration and acoustic measurements) have been employed to detect abnormal combustion phenomena provoked through the enrichment of the hydrogen-air mixture fed to the cylinders under a wide range of engine speeds (1000–5000 rpm). It has been found that the high-frequency components of the in-cylinder pressure and block engine acceleration signals obtained after a Fourier transform analysis can be used for very sensitive detection of knocking combustion cycles. In the case of the ambient noise measurements, a spectral analysis in terms of third octave bands of the signal recorded by a microphone allowed an accurate characterization. Combustion anomalies could be detected through more intense octave bands at frequencies between 250 Hz and 4 kHz in the case of backfire and between 8 kHz and 20 kHz for knock. Computational fluid dynamics simulations performed indicated that some characteristics of the engine used such as the cylinder valves dimensions and the hydrogen flow rate delivered by the injectors play important roles conditioning the likelihood of suffering backfire events., LMG and PMD thank the Spanish Ministerio de Economía, Industria y Competitividad (MINECO) and the European Regional Development Fund (ERDF/FEDER) for the financial support under project ENE2015-66975-C3-1-R.

El objetivo último de esta tesis doctoral es formular catalizadores de Rh y Co y desarrollar, a partir de las mejores formulaciones, sistemas catalíticos estructurados para la producción de gas de síntesis mediante el reformado de biogás. Se han considerado como rutas de reformado las reacciones de reformado seco y su combinación con la oxidación parcial de metano, a través del reformado combinado de tipo ‘oxy‐CO2’., Financiación recibida del Ministerio de Economía, Industria y Competitividad (Proyecto ENE2015‐66975‐C3); Ayuda para Contratos Pre‐doctorales para la Formación de Doctores 2016 (BES‐2016‐077866)., Programa de Doctorado en Ciencias y Tecnologías Industriales (RD 99/2011), Industria Zientzietako eta Teknologietako Doktoretza Programa (ED 99/2011)

There is still a need for active, selective and stable heterogeneous catalysts for the synthesis of biodiesel. In this work, magnesium-aluminium hydrotalcites with Mg/Al molar ratios within the 1.5–5 range were synthesized by coprecipitation and used as transesterification catalysts for the synthesis of biodiesel. The mixed oxides obtained after calcination recovered the hydrotalcite structure in the form of meixnerite after rehydration in boiling water. The solids were characterized by XRD, TGA, N adsorption-desorption, and SEM. Basic properties were assessed by means of Hammett indicators and CO-TPD. Rehydrated materials with the highest Mg/Al ratios showed some distinctive features: low surface area, well defined flake-like crystals, high basicity and strong basic sites with H_ values above 11. They were also the most active catalysts allowing to achieve 51–75% sunflower oil methanolysis conversion after 8 h of reaction under mild conditions (60 °C, 1 atm), methanol/oil molar ratio of 12 using between 2 and 6 wt% of catalyst. The conversion increased up to 96% (92% fatty acid methyl esters yield) using 2 wt% catalyst and methanol/oil molar ratio of 48. Catalyst leaching was not a serious problem with these solids that could be reutilized maintaining very good activities. A general accordance between solids basic properties and their catalytic performance has been observed. These results are among the best reported in the literature for heterogeneous methanolysis catalysts and have been attributed to the high basicity of the rehydrated solids and the presence of strong and accessible basic sites probably consisting in interlayer hydroxide anions at the edges of the crystals., The authors thank the Spanish Ministerio de Economía y Competitividad (MINECO), the former Ministerio de Ciencia e Innovación (prj. refs. TRACE, TRA2009_0265 and ENE2015-66975-C3-1-R) and the European Regional Development Fund (ERDF/FEDER) for the financial support. MINECO and FEDER are also acknowledged for the pre-doctoral aid awarded to Ainara Moral (Ref. num. BES-2013-062799) funded under the ENE2015-66975-C3-1-R project (“Structured Catalytic Systems for Biofuels Production”). J.E., O.S. and M.M. acknowledge the Basque Government (IT1069-16) and the Spanish MINECO/FEDER (ENE2015-66975-C3-3-R and CTQ2015-73901-JIN) for the financial support.