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Considering the renewable electricity production using sustainable technologies, such as solar photovoltaics or wind turbines, it is essential to have systems that allow for storing the energy produced during the periods of lower consumption as well as the energy transportation through the distribution network. Despite hydrogen being considered a good candidate, it presents several problems related to its extremely low density, which requires the use of very high pressures to store it. In addition, its energy density in volumetric terms is still clearly lower than that of most liquid fuels. These facts have led to the consideration of ammonia as an alternative compound for energy storage or as a carrier. In this sense, this review deals with the evaluation of using green ammonia for different energetic purposes, such as an energy carrier vector, an electricity generator and E-fuel. In addition, this study has addressed the latest studies that propose the use of nitrogen-derived compounds, i.e., urea, hydrazine, ammonium nitrate, etc., as alternative fuels. In this study, the possibility of using other nitrogen-derived compounds, i.e., an update of the ecosystem surrounding green ammonia, has been assessed, from production to consumption, including storage, transportation, etc. Additionally, the future challenges in achieving a technical and economically viable energy transition have been determined.

La presente Tesis Doctoral abarca la síntesis y caracterización de catalizadores de naturaleza ácida con diferentes propiedades estructurales y texturales, y su aplicación en la reacción de eterificación de glicerol con tert-butanol, para obtener los di- y tri-éteres (high ethers) que son empleados como aditivos oxigenados para combustibles. Además, se ha evaluado el carbonato de dimetilo como un disolvente renovable para reducir la alta viscosidad del aceite de ricino y del aceite de girasol (representando al aceite usado) y obtener, así, biocombustibles de segunda generación aptos para los motores diésel actuales. En el artículo “Sulfonated carbons from olive stones as catalysts in the microwave-assisted etherification of glycerol with tert-butyl alcohol” se han sintetizado materiales basados en carbón, utilizando como materia prima el hueso de aceituna, que es un importante residuo en Andalucía, región productora por excelencia de aceite de oliva del mundo. El carbón ha sido tratado con H2SO4 con el fin de incorporar grupos sulfónico en su estructura, empleando calefacción convencional y microondas, a diferentes temperaturas (100 y 150 ᵒC) y tiempos de reacción (0.5, 2 y 5 h). Los sólidos han sido exhaustivamente caracterizados y testados en la reacción de eterificación de glicerol con tert-butanol bajo irradiación microondas. A modo comparativo, se ha empleado también calefacción convencional. En el artículo “Sulfonated organosilica-aluminum phosphates as useful catalysts for acid-catalyzed reactions: Insights into the effect of synthesis parameters on the final catalyst” se ha llevado a cabo la optimización de la síntesis, mediante un método sol-gel, de silicoaluminofosfatos con grupos sulfónico en su estructura, variando la relación Al/P (3-10), el pH final de síntesis (3-9) y el tipo de compuesto organosilano. Se han empleado tres organosilanos diferentes, uno de ellos contiene el grupo sulfónico en su estructura y los otros dos grupos tiol y tetrasulfuro, respectivamente, que deben ser oxidados posteriormente a grupos sulfónico. El objetivo es mejorar la incorporación de grupos sulfónico, a través de la interacción de las especies de Si y Al, y preparar materiales con diferente porosidad, a fin de lograr mejores resultados que los obtenidos previamente por nuestro Grupo de Investigación. Los sólidos sintetizados han sido empleados en la reacción de eterificación de glicerol con tert-butanol bajo irradiación microondas. En el artículo “Evaluation of dimethyl carbonate as alternative biofuel. Performance and smoke emissions of a diesel engine fueled with diesel/dimethyl carbonate/straight vegetable oil triple blends” se ha evaluado el carbonato de dimetilo (DMC) como biodisolvente de dos aceites vegetales, aceite de ricino y aceite de girasol (representando al aceite usado), en la obtención de nuevos biocombustibles de segunda generación, que puedan ser empleados en los vehículos actuales sin necesidad de modificaciones de los motores. Para ello, los diferentes biocombustibles (mezcla DMC/aceite vegetal) han sido añadidos al diésel en diferentes proporciones del 20% al 80% en volumen. Se han determinado propiedades físico-químicas de los combustibles que influyen directamente en el rendimiento de un motor de combustión interna, como la viscosidad, la densidad, las propiedades de flujo en frío, el número de cetano y el valor calorífico. La eficacia de los diferentes biocombustibles se ha evaluado en base a la potencia generada por un motor diésel, las emisiones de hollín generadas y el consumo de combustible. Además de lo indicado anteriormente, durante una estancia de 3 meses realizada en el “Istituto per lo studio dei Materiali Nanostrutturati (ISMN) del Dipartimento di scienze chimiche e tecnologie dei materiali (DSCTM) del Consiglio Nazionale delle Ricerche (CNR)” situado en Palermo (Italia), se sintetizaron materiales basados en sílice funcionalizados con grupos ácidos y/o básicos. Estos materiales serán testados en reacciones de transformación de la biomasa, que requieren de dichos centros, para obtener productos de interés en Química Fina e Industrial como aditivos oxigenados para combustibles, entre otros. The Doctoral Thesis covers the synthesis and characterization of acidic catalysts with different structural and textural properties, and their application in the etherification reaction of glycerol with tert-butyl alcohol, in order to obtain the di- and tri-ethers (high ethers), which are used as oxygenated additives for fuels. In addition, dimethyl carbonate has been evaluated as a renewable solvent to reduce the high viscosity of castor oil and sunflower oil (as a reference for waste cooking oils) and obtain, thus, suitable second-generation biofuels for use in current diesel engines In the article "Sulfonated carbons from olive stones as catalysts in the microwave-assisted etherification of glycerol with tert-butyl alcohol" carbon-based materials have been prepared from olive stones, which are an important waste in Andalusia, the world's leading olive oil-producing region. The carbon has been treated with H2SO4 in order to incorporate sulfonic groups in its structure, using either conventional heating or microwave irradiation, at different temperatures (100 and 150 ᵒC) and reaction times (0.5, 2 and 5 h). The solids have been exhaustively characterized and tested in the etherification reaction of glycerol with tert-butyl alcohol using microwave as way of heating. For comparison, conventional heating has also been employed. In the article "Sulfonated organosilica-aluminum phosphates as useful catalysts for acid-catalyzed reactions: Insights into the effect of synthesis parameters on the final catalyst" the optimization of the synthesis, by a sol-gel method, of organosilica-aluminum phosphates with sulfonic groups in their structure, varying the Al/P ratio (3-10), the final synthesis pH (3-9) and the type of organosilane compound, has been carried out. Three different organosilanes have been employed, one of them containing the sulfonic group in its structure and the other two thiol and tetrasulfide groups, respectively, which are subsequently oxidized to sulfonic groups. The goal is to enhance the incorporation of sulfonic groups, through the interaction between the species of Si and Al, and to prepare materials with tunable porosity, in order to attain better results than those previously obtained by our Research Group. The synthesized solids have been tested in the etherification reaction of glycerol with tert-butyl alcohol under microwave irradiation. In the article “Evaluation of dimethyl carbonate as alternative biofuel. Performance and smoke emissions of a diesel engine fueled with diesel/dimethyl carbonate/straight vegetable oil triple blends” dimethyl carbonate (DMC) has been evaluated as a bio-solvent of both vegetable oils castor oil and sunflower oil (as a reference for waste cooking oils), for obtaining new second-generation biofuels that can be used in current vehicles without engine modifications. Thus, different volumetric proportions of biofuel (DMC/vegetable oil blend), from 20% to 80%, have been added to diesel. Several important fuel properties for the performance of an internal combustion engine, such as viscosity, density, cold flow properties, cetane number and calorific value, have been determined. The efficiency of the different biofuels has been evaluated based on the power generated by a diesel engine; the soot emissions generated and the fuel consumption. In addition to the aforementioned, silica-based materials functionalized with acid and/or basic groups were synthesized during a 3-month stay at the "Istituto per lo study dei Materiali Nanostrutturati (ISMN) del Dipartimento di scienze chimiche e tecnologie dei materiali (DSCTM) del Consiglio Nazionale delle Ricerche (CNR)" located in Palermo (Italy). These materials will be tested in biomass transformation reactions, which require these centers, to obtain value-added chemicals for Fine and Industrial Chemistry, such as oxygenated additives for fuels, among them.

Embargado hasta 31/01/2024 The synthesis, by a sol-gel method, of organosilica-aluminum phosphates, (X)-AlPO(Y)-(Z), using three different silica precursors (X) 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (C), 3-(mercaptopropyl)trimethoxysilane (MPTMS) or Bis[3-(triethoxysilyl)propyl]tetrasulfide (B), with varying Al/P molar ratio (Y = 3–10) and pH of the final gel (Z = 3–9), maintaining an Al/Si= 3 molar ratio, has been carried out. Materials were characterized by XRF, SEM-EDX, XRD, 1H–29Si CP, 27Al and 31P MAS NMR and nitrogen adsorption. The acidity of the solids was evaluated by TGA, XRF and XPS and their catalytic behavior in the etherification of glycerol with tert-butyl alcohol, under microwave irradiation. The solids with an Al/P molar ratio between 3 and 6, synthesized at a pH value over 3 with precursor C, exhibiting the highest values of acidity and predominantly a mesoporous character, showed the best catalytic behavior.

Resumen de la publicación de una participación en formato µVídeo en en el congreso Divulga NextGen (1ª edición) que se celebrará online, de manera gratuita y en las redes sociales los días 26, 27 y 28 de mayo de 2021., MINECO-ENE2016-81013-R (AEI/FEDER, EU), MICIIN (Project ref. PID2019-104953RB-100), UCO-FEDER Project CATOLIVAL, ref. 1264113-R, 2018 call y PAIDI 2020 Project ref. P18-RT-4822., {"references":["L. Aguado-Deblas, J. Hidalgo-Carrillo, F. Bautista, C. Luna, J. Calero, A. Posadillo, A. Romero, D. Luna, R. Estevez, Evaluation of dimethyl carbonate as alternative biofuel. Performance and smoke emissions of a diesel engine fueled with diesel/dimethyl carbonate/straight vegetable oil triple blends, Sustainability 13 (2021) 1749-1762."]}