Reformado con vapor de bio-oil: condiciones para el proceso en dos etapas y modelo cinético

358 p.Se ha estudiado la producción de H2 mediante reformado catalítico con vapor de bio-oil (SRB), utilizando un equipo de reacción con dos etapas: i) tratamiento térmico del bio-oil, y ii) reformado en línea con catalizador de Ni/La2O3-¿Al2O3 en reactor de lecho fluidizado, y utilizando dos alimentaciones diferentes: i) mezcla de bio-oil completo, estabilizada con un 20 % de etanol y ii) bio-oil completo. El análisis del efecto de la temperatura en la etapa térmica sobre la composición del bio-oil y sobre el rendimiento y composición de la lignina pirolítica (LP) ha permitido delimitar la temperatura adecuada para maximizar la fracción de bio-oil valorizable a H2 y establecer posibles vías de valorización de la LP. Se ha estudiado el efecto de las temperaturas de calcinación (550 - 850 ºC) y de reducción (700 - 850 ºC) sobre las propiedades y el comportamiento cinético del catalizador, determinando las temperaturas de ambas etapas que maximizan la actividad, selectividad de H2 y estabilidad del catalizador. Para la mezcla bio-oil/etanol se ha estudiado el comportamiento de dolomita calcinada bien como catalizador de bajo coste para su valorización parcial, o bien para su uso en un proceso integrado con dos etapas catalíticas en serie: i) pre-reformado con dolomita; ii) reformado en línea con el catalizador de Ni, analizando el efecto de la temperatura en el reactor de pre-reformado (400-700 ºC) y del tiempo espacial en cada etapa sobre la conversión, rendimientos de productos y estabilidad del catalizador de Ni.Se ha analizado el efecto de las condiciones de operación (temperatura, tiempo espacial y relación molar S/C) sobre los índices de reacción (conversión y rendimientos) a tiempo cero y sobre su evolución con el tiempo en el reformado del bio-oil completo con el catalizador Ni/La2O3-¿Al2O3, lo que ha permitido delimitar las condiciones óptimas para maximizar la producción de H2 con un comportamiento estable del catalizador, así como obtener datos cinéticos suficientes para abordar con rigor el modelado cinético del proceso. Mediante comparación de los resultados de contenido, naturaleza y ubicación del coque (determinados por Oxidación a Temperatura Programada (TPO) del catalizador desactivado) con la composición del medio de reacción y la velocidad de desactivación observada, se han delimitado los precursores del coque y responsables de la desactivación del catalizador.Se ha establecido un modelo cinético para el SRB sobre catalizador Ni/La2O3-¿Al2O3, que incluye en las expresiones de velocidad de reacción a tiempo cero la posible contribución de las rutas térmicas (en ausencia de catalizador), y que contempla la desactivación del catalizador. La ecuación cinética de desactivación de mejor ajuste tiene un orden de desactivación de 2.5, e incluye a los compuestos oxigenados del bio-oil como precursores de la desactivación por coque. El modelo ajusta razonablemente bien la evolución con el tiempo de reacción de la distribución de los productos de reacción (H2, CO, CO2, CH4, hidrocarburos y oxigenados del bio-oil) en un amplio intervalo de condiciones de operación: 550-700 ºC; tiempo espacial, 0.04-0.38 gcatalizadorh/gbio-oil; relación molar S/C entre 1.5- 6.0

Reformado con vapor de bio-oil: condiciones para el proceso en dos etapas y modelo cinético

358 p.Se ha estudiado la producción de H2 mediante reformado catalítico con vapor de bio-oil (SRB), utilizando un equipo de reacción con dos etapas: i) tratamiento térmico del bio-oil, y ii) reformado en línea con catalizador de Ni/La2O3-¿Al2O3 en reactor de lecho fluidizado, y utilizando dos alimentaciones diferentes: i) mezcla de bio-oil completo, estabilizada con un 20 % de etanol y ii) bio-oil completo. El análisis del efecto de la temperatura en la etapa térmica sobre la composición del bio-oil y sobre el rendimiento y composición de la lignina pirolítica (LP) ha permitido delimitar la temperatura adecuada para maximizar la fracción de bio-oil valorizable a H2 y establecer posibles vías de valorización de la LP. Se ha estudiado el efecto de las temperaturas de calcinación (550 - 850 ºC) y de reducción (700 - 850 ºC) sobre las propiedades y el comportamiento cinético del catalizador, determinando las temperaturas de ambas etapas que maximizan la actividad, selectividad de H2 y estabilidad del catalizador. Para la mezcla bio-oil/etanol se ha estudiado el comportamiento de dolomita calcinada bien como catalizador de bajo coste para su valorización parcial, o bien para su uso en un proceso integrado con dos etapas catalíticas en serie: i) pre-reformado con dolomita; ii) reformado en línea con el catalizador de Ni, analizando el efecto de la temperatura en el reactor de pre-reformado (400-700 ºC) y del tiempo espacial en cada etapa sobre la conversión, rendimientos de productos y estabilidad del catalizador de Ni.Se ha analizado el efecto de las condiciones de operación (temperatura, tiempo espacial y relación molar S/C) sobre los índices de reacción (conversión y rendimientos) a tiempo cero y sobre su evolución con el tiempo en el reformado del bio-oil completo con el catalizador Ni/La2O3-¿Al2O3, lo que ha permitido delimitar las condiciones óptimas para maximizar la producción de H2 con un comportamiento estable del catalizador, así como obtener datos cinéticos suficientes para abordar con rigor el modelado cinético del proceso. Mediante comparación de los resultados de contenido, naturaleza y ubicación del coque (determinados por Oxidación a Temperatura Programada (TPO) del catalizador desactivado) con la composición del medio de reacción y la velocidad de desactivación observada, se han delimitado los precursores del coque y responsables de la desactivación del catalizador.Se ha establecido un modelo cinético para el SRB sobre catalizador Ni/La2O3-¿Al2O3, que incluye en las expresiones de velocidad de reacción a tiempo cero la posible contribución de las rutas térmicas (en ausencia de catalizador), y que contempla la desactivación del catalizador. La ecuación cinética de desactivación de mejor ajuste tiene un orden de desactivación de 2.5, e incluye a los compuestos oxigenados del bio-oil como precursores de la desactivación por coque. El modelo ajusta razonablemente bien la evolución con el tiempo de reacción de la distribución de los productos de reacción (H2, CO, CO2, CH4, hidrocarburos y oxigenados del bio-oil) en un amplio intervalo de condiciones de operación: 550-700 ºC; tiempo espacial, 0.04-0.38 gcatalizadorh/gbio-oil; relación molar S/C entre 1.5- 6.0

Influence of AISI D2 Workpiece Roughness on Heat Partition and Plasma Channel Radius in the WEDM Process

As an important advanced machining process, in Wire Electrical Discharge Machining (WEDM) certain fundamental issues remain need to be studied in-depth, such as the effect of part surface roughness on heat transfer mechanisms. In the WEDM process, roughing cut wire goes into the workpiece to do the first shaping and in trim cut the wire sweeps on the outer surface to improve the surface roughness. In both of these two cases, the generation of sparks depends on the passing surface roughness. Therefore, with AISI D2 material and brass wire, this paper presents a study of the influence of part surface roughness on heat partition and the radius of the plasma channel in the WEDM process. Through extensive single discharge experiments, it is shown that the removal capacity per discharge can increase if the discharge occurs on a smoother surface. A Finite Element thermal model was then used for inverse fitting of the values of heat partition and radius of the plasma channel. These parameters completely define the characteristics of the heat conduction problem. The results indicate a strong correlation between an increase in heat partition ratio and a decrease in part surface roughness. The values of plasma channel radius show an increase in this value when discharging on rougher surfaces. It means that with the increasing of plasma channel radius, the heat source goes into the workpiece more dispersed. In the case of rougher surface, although the there is more area that affected by the heat source, finally the temperature of most area cannot reach to the melting point and it causes the smaller crater radius and volume, while the metal removal rate decreases. These results contribute towards a more complete understanding of the influence of surface roughness to the spark occurring.This research was funded by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (ERDF) operation program for funding the project “Scientific models and machine-tool advanced sensing techniques for efficient machining of precision components of Low-Pressure Turbines” (DPI2017-82239-P)

An Original Tribometer to Analyze the Behavior of Abrasive Grains in the Grinding Process

Manufacturing of grinding wheels is continuously adapting to new industrial requirements. New abrasives and new wheel configurations, together with wheel wear control allow for grinding process optimization. However, the wear behavior of the new abrasive materials is not usually studied from a scientific point of view due to the difficulty to control and monitor all the variables affecting the tribochemical wear mechanisms. In this work, an original design of pin-on-disk tribometer is developed in a CNC (Computer Numerical Control) grinding machine. An Alumina grinding wheel with special characteristics is employed and two types of abrasive are compared: White Fused Alumina (WFA) and Sol-Gel Alumina (SG). The implemented tribometer reaches sliding speeds of between 20 and 30 m/s and real contact pressures up to 190 MPa. The results show that the wear behavior of the abrasive grains is strongly influenced by their crystallographic structure and the tribometer appears to be a very good tool for characterizing the wear mechanisms of grinding wheels, depending on the abrasive grains.The authors gratefully acknowledge the funding support received from the Spanish Ministry of Economy and Competitiveness and the FEDER operation program for funding the project "Scientific models and machine-tool advanced sensing techniques for efficient machining of precision components of Low Pressure Turbines" (DPI2017-82239-P). Funding support was also received from the contracting call for the training of research staff in UPV/EHU 2016, of Vice-rectorate of research to develop this project

Implicit Subspace Iteration to Improve the Stability Analysis in Grinding Processes

An alternative method is devised for calculating dynamic stability maps in cylindrical and centerless infeed grinding processes. The method is based on the application of the Floquet theorem by repeated time integrations. Without the need of building the transition matrix, this is the most efficient calculation in terms of computation effort compared to previously presented time-domain stability analysis methods (semi-discretization or time-domain simulations). In the analyzed cases, subspace iteration has been up to 130 times faster. One of the advantages of these time-domain methods to the detriment of frequency domain ones is that they can analyze the stability of regenerative chatter with the application of variable workpiece speed, a well-known technique to avoid chatter vibrations in grinding processes so the optimal combination of amplitude and frequency can be selected. Subspace iteration methods also deal with this analysis, providing an efficient solution between 27 and 47 times faster than the abovementioned methods. Validation of this method has been carried out by comparing its accuracy with previous published methods such as semi-discretization, frequency and time-domain simulations, obtaining good correlation in the results of the dynamic stability maps and the instability reduction ratio maps due to the application of variable speed

Viability of Glycolysis for the Chemical Recycling of Highly Coloured and Multi-Layered Actual PET Wastes

The chemical recycling of poly(ethylene terephthalate) –PET– fractions, derived from actual household packaging waste streams, using solvolysis, was investigated. This recycling strategy was applied after a previous on-line automatic identification, by near-infrared spectroscopy –NIR–, and a subsequent selective sorting of the different PET materials that were present in the packaging wastes. Using this technology, it was possible to classify fractions exclusively including PET, virtually avoiding the presence of both other plastics and materials, such as paper, cardboard and wood, that are present in the packaging wastes, as they were efficiently recognised and differentiated. The simple PET fractions, including clear and monolayered materials, were adequate to be recycled by mechanical means meanwhile the complex PET fractions, containing highly coloured and multi-layered materials, were suitable candidates to be recycled by chemical routes. The depolymerisation capacity of the catalytic glycolysis, when applied to those complex PET wastes, was studied by evaluating the effect of the process parameters on the resulting formation and recovery of the monomer bis(2-hydroxyethyl) terephthalate –BHET– and the achieved quality of this reaction product. Comparable and reasonable results, in terms of monomer yield and its characteristics, were obtained independently of the type of complex PET waste that was chemically recycled.This research was funded by the Department of Economic Development, Sustainability and Environment of The Basque Government by its ELKARTEK 2023 Program (NEOPLAST 2 Project, Reference KK-2023/00060), and also by CDTI (Centro para el Desarrollo Tecnológico Industrial), within the framework of grants for Technological Centres of Excellence “Cervera” (OSIRIS Project, CER-20211009)

Impurities bound to vacancies in insulators: electronic relaxation and physical properties of the Cr 3 + − V M model center in K M F 3 ( M = Mg, Zn)

This work is aimed at gaining a better insight into the influence of a close vacancy, V, on the properties of impurities in insulating materials. To achieve this goal the Cr3+−VM model center formed in KMF3 (M = Mg, Zn) fluoroperovskites has been explored in detail by means of ab initio calculations on clusters involving up to 87 ions. It is shown that the presence of the M2+ vacancy, VM, induces a significant structural relaxation on the CrF3−6 cubic complex which cannot be fully understood assuming that ions were rigid spheres that could not be polarized. Thus, although VM forces all the ligands to move away, the Cr3+−F− distance corresponding to the furthest ligand, Ffar, is found to be slightly higher than that for the closer equatorial ions. This unexpected fact is shown to be due to the electronic relaxation also induced by VM on the CrF3−6 complex, causing a charge of 0.2e to be transferred from the closest ligand to VM, Fnext, mainly to Ffar, and, to a lesser extent, to any equatorial ligand. This transfer of charge is mainly accomplished through orbitals lying in planes containing the C4 axis. In spite of these changes due to the vacancy, the 4A2g→4T2g optical transition is found to be weakly altered, a fact that concurs with available experimental data and whose origin is discussed. In contrast, electron paramagnetic resonance parameters such as gyromagnetic or superhyperfine tensors, which do depend on the electronic density around a point of the CrF3−6 complex, are shown to be particularly sensitive to the electronic relaxation induced by VM. In particular, the present study explains that the dominant component of the superhyperfine tensor for the Fnext ligand is clearly higher than that for Ffar, in agreement with experimental data. The relevance of the present results for understanding the electronic properties of other systems involving vacancies is also discussed. Some results on the Cr3+−Li+ center formed in KMgF3 are also discussed for comparison.The support by the Spanish Ministerio de Ciencia y Tecnología under Project FIS2009-07083 is acknowledge

Influence of the COVID-19 Pandemic on the Lifestyles of Health Sciences University Students in Spain: A Longitudinal Study

The COVID-19 pandemic has significantly impacted daily activities worldwide. University students may have experienced substantial changes in daily living as a result of restrictions on university attendance. The return to normalcy may take a long time, and understanding the influence that shifts in daily routines have had on the lifestyles of university students may inform approaches to support overall well-being. We analyzed changes in the lifestyles of students enrolled at a health sciences university during the COVID-19 pandemic. This longitudinal study took place at the Faculty of Medicine and Nursing in the University of the Basque Country in Spain, and the final sample consisted of 113 nursing students, 109 medical students, and 45 physiotherapy students. Our results demonstrate changes in lifestyles of university students during the pandemic. MedDiet adherence scores and the percentage of students with high adherence increased during the pandemic. This increase was due to the increased consumption of vegetables and nuts. In terms of physical activity, the practice of moderate and intense physical activity was maintained. These results provide important information for both public health authorities and educational institutions to guide strategies to maintain the well-being of students and enhance opportunities for young adults to lead a healthy lifestyle.This research was funded by the Official College of Nursing of Gipuzkoa (COEGI), grant number S0040/2020

Ivabradine in acute heart failure: Effects on heart rate and hemodynamic parameters in a randomized and controlled swine trial

Background: Acute heart failure patients could benefit from heart rate reduction, as myocardial consumption and oxidative stress are related to tachycardia. Ivabradine could have a clinical role attenuating catecholamine-induced tachycardia. The aim of this study was to evaluate hemodynamic effects of ivabradine in a swine model of acute heart failure. Methods: Myocardial infarction was induced by 45 min left anterior descending artery balloon occlusion in 18 anesthetized pigs. An infusion of dobutamine and noradrenaline was maintained aiming to preserve adequate hemodynamic support, accompanied by fluid administration to obtain a pulmonary wedged pressure ≥ 18 mmHg. After reperfusion, rhythm and hemodynamic stabilization, the animals were randomized to 0.3 mg/kg ivabradine intravenously (n = 9) or placebo (n = 9). Hemodynamic parameters were observed over a 60 min period. Results: Ivabradine was associated with a significant reduction in heart rate (88.4 ± 12.0 bpm vs. 122.7 ± 17.3 bpm after 15 min of ivabradine/placebo infusion, p < 0.01) and an increase in stroke volume (68.8 ± 13.7 mL vs. 52.4 ± 11.5 mL after 15 min, p = 0.01). There were no significant differences in systemic or pulmonary arterial pressure, or significant changes in pulmonary capillary pressure. However, after 15 min, cardiac output was significantly reduced with ivabradine (–5.2% vs. +15.0% variation in ivabradine/placebo group, p = 0.03), and central venous pressure increased (+4.2% vs. –19.7% variation, p < 0.01). Conclusions: Ivabradine reduces heart rate and increases stroke volume without modifying systemic or left filling pressures in a swine model of acute heart failure. However, an excessive heart rate reduction could lead to a decrease in cardiac output and an increase in right filling pressures. Future studies with specific heart rate targets are needed

Ivabradine in acute heart failure: Effects on heart rate and hemodynamic parameters in a randomized and controlled swine trial.

Background: Acute heart failure patients could benefit from heart rate reduction, as myocardial consumption and oxidative stress are related to tachycardia. Ivabradine could have a clinical role attenuating catecholamine-induced tachycardia. The aim of this study was to evaluate hemodynamic effects of ivabradine in a swine model of acute heart failure. Methods: Myocardial infarction was induced by 45 min left anterior descending artery balloon occlusion in 18 anesthetized pigs. An infusion of dobutamine and noradrenaline was maintained aiming to preserve adequate hemodynamic support, accompanied by fluid administration to obtain a pulmonary wedged pressure ≥ 18 mmHg. After reperfusion, rhythm and hemodynamic stabilization, the animals were randomized to 0.3 mg/kg ivabradine intravenously (n = 9) or placebo (n = 9). Hemodynamic parameters were observed over a 60 min period. Results: Ivabradine was associated with a significant reduction in heart rate (88.4 ± 12.0 bpm vs. 122.7 ± 17.3 bpm after 15 min of ivabradine/placebo infusion, p < 0.01) and an increase in stroke volume (68.8 ± 13.7 mL vs. 52.4 ± 11.5 mL after 15 min, p = 0.01). There were no significant differences in systemic or pulmonary arterial pressure, or significant changes in pulmonary capillary pressure. However, after 15 min, cardiac output was significantly reduced with ivabradine (–5.2% vs. +15.0% variation in ivabradine/placebo group, p = 0.03), and central venous pressure increased (+4.2% vs. – 19.7% variation, p < 0.01). Conclusions: Ivabradine reduces heart rate and increases stroke volume without modifying systemic or left filling pressures in a swine model of acute heart failure. However, an excessive heart rate reduction could lead to a decrease in cardiac output and an increase in right filling pressures. Future studies with specific heart rate targets are needed.pre-print2533 K