Prozessintensivierung für die Wasserstofffreisetzung aus flüssigen organischen Wasserstoffträgern

The dehydrogenation of perhydro dibenzyltoluene (H18-DBT) in a fixed-bed tubular reactor can be considered as state of the art. However, there is a considerable potential for improvement in the continuous dehydrogenation of H18-DBT. In this thesis mixtures of perhydro benzyltoluene (H12-BT) and H18-DBT were investigated to improve the handling of the LOHC and the productivity of the dehydrogenation. The stability of the catalyst was investigated in a continuous reactor. Additionally, alternative reactor concepts were evaluated to increase the productivity and decrease the dehydrogenation temperature. As part of this thesis mixtures of H12-BT and H18-DBT were examined in the dehydrogenation. With increasing amount of H12 BT in H18 DBT the viscosity decreases and the vapor pressure of the mixture increases. The handling of the LOHC simplifies with increasing amount of H12-BT, however, the maximum dehydrogenation temperature for a liquid phase dehydrogenation at atmospheric pressure decreases with increasing amount of H12-BT. Furthermore, the influence of the concentration of H12-BT in the mixture on hydrogen release in batch dehydrogenation was determined. At a constant temperature, the productivity increases with increasing amount of H12-BT. Another focus of this work was to investigate the continuous dehydrogenation of H18-DBT in a cuboid fixed-bed reactor. In the cuboid reactor the productivity can be increased compared to a tubular reactor. In addition, the stability of the catalyst was investigated over several cooling down procedures. Furthermore, the reactor was characterized with respect to its residence time behavior and a model was developed to determine the released hydrogen volume flow depending on the temperature, the pressure and the supplied volume flow of H18-DBT. Finally, the reactor concept of reactive distillation was evaluated. In this reactor concept the evaporation of the LOHC is desirable, since the process temperature corresponds to the boiling temperature of the LOHC due to the integrated distillation process. H12-BT is used as LOHC, since the boiling point is below the thermal stability limit of the LOHC at atmospheric pressure unlike the technically established LOHC H18-DBT. The product inhibition in the liquid-phase dehydrogenation of H12-BT was first demonstrated. Furthermore, batch experiments indicate that product inhibition can be reduced in the reactive distillation concept. Additionally, the influence of pressure on bottom and catalyst temperature was investigated. By reducing pressure, the bottom and catalyst temperature can be decreased, as pressure and boiling temperature are coupled. Thus, heat integration seems possible between endothermal dehydrogenation and an exothermal HT-PEMFC. So, the efficiency of energy conversion from LOHC-bound hydrogen to electricity can be increased. However, the decreasing temperature in the catalyst bed reduces the productivity in dehydrogenation with decreasing pressure. Based on the results of the batch experiments, a continuous laboratory-scale experimental setup was developed. Stable continuous dehydrogenation at ambient and negative pressure could be demonstrated. In addition, an intensification of the dehydrogenation could be shown by the reactor concept of reactive rectification compared to the classical liquid phase dehydrogenation in a fixed-bed reactor.Die Dehydrierung von Perhydro Dibenzyltoluol (H18-DBT) in einem Festbettrohrreaktor kann als Stand der Technik angesehen werden. Allerdings hat die kontinuierliche Dehydrierung von H18-DBT noch erhebliches Verbesserungspotential. In dieser Arbeit wurde die Verbesserung der Handhabbarkeit und die Steigerung der Produktivität durch die Modifizierung des LOHCs, die Verbesserung der Stabilität des Katalysators und die Entwicklung alternativer Reaktorkonzepte zur Absenkung der Reaktionstemperatur und Steigerung der Produktivität untersucht. Im Rahmen dieser Arbeit wurde der Einsatz von Mischungen aus Perhydro-Benzyltoluol (H12-BT) und H18-DBT in der Dehydrierung untersucht. Mit steigendem Anteil an H12-BT in H18-DBT sinkt die Viskosität und steigt der Dampfdruck der Mischung. So wird die Handhabbarkeit mit steigendem Anteil an H12-BT verbessert, jedoch reduziert sich mit steigendem Anteil an H12-BT die maximale Temperatur einer Flüssigphasen-Dehydrierung bei atmosphärischem Druck. Weiterhin wurde der Einfluss des Anteils an H12-BT auf die Wasserstofffreisetzung in der Batch-Dehydrierung betrachtet. Bei konstanter Temperatur erhöht sich die Produktivität mit steigendem Anteil an H12-BT. Ein weiterer Schwerpunkt der Arbeit lag in der Untersuchung der kontinuierlichen Dehydrierung von H18-DBT in einem Festbettreaktor mit rechteckigem Querschnitt. Durch die Verwendung eines rechteckigen Querschnitts kann die Wasserstofffreisetzungsrate im Gegensatz zum kreisförmigen Querschnitt gesteigert werden. Zusätzlich wurde in diesem Reaktor die Stabilität des Katalysators über mehrere Abkühl- und Aufheizvorgänge untersucht. Außerdem wurde der Reaktor hinsichtlich seines Verweilzeitverhaltens charakterisiert und ein Modell entwickelt, um abhängig von der Temperatur, dem Druck und dem zugeführten Volumenstrom an H18-DBT den freigesetzten Wasserstoffvolumenstrom ermitteln zu können. Abschließend wird das Reaktorkonzept der Reaktivrektifikation evaluiert. In diesem Reaktorkonzept entspricht die Prozesstemperatur aufgrund der integrierten Rektifikation der Siedetemperatur des LOHCs. Als LOHC wird in diesem Reaktorkonzept H12-BT verwendet, da bei H12-BT der Siedepunkt bei atmosphärischem Druck unter der erlaubten Verwendungstemperatur im Gegensatz zum technisch etablierten LOHC H18-DBT liegt. Zunächst wurde die Produktinhibierung in der Flüssigphasen-Dehydrierung von H12-BT nachgewiesen. Batch-Versuche deuten darauf hin, dass in einem Reaktivrektifikationskonzept die Produktinhibierung reduziert werden kann. Außerdem wurde der Einfluss des Drucks auf die Sumpf- und Katalysatortemperatur untersucht. Durch die Reduzierung des Drucks reduziert sich die Sumpf- und Katalysatortemperatur. Dadurch scheint die Einbringung der Dehydrierwärme durch Wärmeintegration mit einer HT-PEMFC möglich. So kann der Wirkungsgrad von im LOHC gespeicherten Wasserstoff zu Strom gesteigert werden. Aufgrund der niedrigeren Reaktionstemperatur reduziert sich die Wasserstofffreisetzung mit sinkendem Druck. Aufbauend auf den Erkenntnissen aus den Batch-Versuchen wurde ein kontinuierlicher Versuchsaufbau im Labormaßstab entwickelt. Es konnte eine stabile kontinuierliche Dehydrierung bei atmosphärischem Druck und Unterdruck gezeigt werden. Zusätzlich konnte eine Intensivierung der Dehydrierung durch das Reaktorkonzept der Reaktivrektifikation im Vergleich zur klassischen Flüssigphasen-Dehydrierung im Festbettreaktor gezeigt werden

Modeling of the Continuous Dehydrogenation of Perhydro‐Dibenzyltoluene in a Cuboid Reactor

The use of the dibenzyltoluene/perhydro‐dibenzyltoluene (H18–DBT) system as a liquid organic hydrogen carrier (LOHC) enables the safe and loss‐free storage of hydrogen. The release of hydrogen from the LOHC is a catalytic reaction and requires ≈27% of the lower heating value of the released hydrogen in the form of heat neglecting heat losses. The high heat requirement makes it necessary to design chemical conversion units that both provide good heat input and accommodate the high gas release. Up to 1200 L of hydrogen is released from 1 L of LOHC under reaction conditions. In this work, a cuboid reactor for the release of hydrogen from H18–DBT is demonstrated. In the experiments, it is shown that evaporation has a significant effect on the reaction rate and thus the amount of hydrogen releases. Therefore, a kinetic model capable of accounting for the release rate and evaporation in the reactor is developed. The model is successfully validated and shows deviations of less than 15% between measured and modeled hydrogen flow in the entire range considered. Since the model considers this important interaction between evaporation and hydrogen release for the first time, it is suitable for optimizing the reactor used.The high heat requirement of the catalytic dehydrogenation makes it necessary to design conversion units that both provide good heat input and accommodate the high gas release. Herein, a cuboid reactor for the release of hydrogen from perhydro‐dibenzyl toluene is presented. For this system, a kinetic model capable of accounting for the release rate and evaporation in the reactor is developed and successfully validated. image © 2024 WILEY‐VCH GmbH Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/50110000234

Event reconstruction for KM3NeT/ORCA using convolutional neural networks

The KM3NeT research infrastructure is currently under construction at two locations in the Mediterranean Sea. The KM3NeT/ORCA water-Cherenkov neutrino de tector off the French coast will instrument several megatons of seawater with photosensors. Its main objective is the determination of the neutrino mass ordering. This work aims at demonstrating the general applicability of deep convolutional neural networks to neutrino telescopes, using simulated datasets for the KM3NeT/ORCA detector as an example. To this end, the networks are employed to achieve reconstruction and classification tasks that constitute an alternative to the analysis pipeline presented for KM3NeT/ORCA in the KM3NeT Letter of Intent. They are used to infer event reconstruction estimates for the energy, the direction, and the interaction point of incident neutrinos. The spatial distribution of Cherenkov light generated by charged particles induced in neutrino interactions is classified as shower-or track-like, and the main background processes associated with the detection of atmospheric neutrinos are recognized. Performance comparisons to machine-learning classification and maximum-likelihood reconstruction algorithms previously developed for KM3NeT/ORCA are provided. It is shown that this application of deep convolutional neural networks to simulated datasets for a large-volume neutrino telescope yields competitive reconstruction results and performance improvements with respect to classical approaches

Event reconstruction for KM3NeT/ORCA using convolutional neural networks

The KM3NeT research infrastructure is currently under construction at two locations in the Mediterranean Sea. The KM3NeT/ORCA water-Cherenkov neutrino detector off the French coast will instrument several megatons of seawater with photosensors. Its main objective is the determination of the neutrino mass ordering. This work aims at demonstrating the general applicability of deep convolutional neural networks to neutrino telescopes, using simulated datasets for the KM3NeT/ORCA detector as an example. To this end, the networks are employed to achieve reconstruction and classification tasks that constitute an alternative to the analysis pipeline presented for KM3NeT/ORCA in the KM3NeT Letter of Intent. They are used to infer event reconstruction estimates for the energy, the direction, and the interaction point of incident neutrinos. The spatial distribution of Cherenkov light generated by charged particles induced in neutrino interactions is classified as shower- or track-like, and the main background processes associated with the detection of atmospheric neutrinos are recognized. Performance comparisons to machine-learning classification and maximum-likelihood reconstruction algorithms previously developed for KM3NeT/ORCA are provided. It is shown that this application of deep convolutional neural networks to simulated datasets for a large-volume neutrino telescope yields competitive reconstruction results and performance improvements with respect to classical approaches