A three-phase reactor assessment for the deployment of Liquid Organic Hydrogen Carriers (LOHCs): dybenzyltoluene and indoles mixture systems as case studies

As a result of the large increase in the production of renewable energies, energy storage and energy carrier systems are required to meet the most ambitious objectives. In this area, hydrogen stands out as one of the most powerful tools. However, its low volumetric energy density and its challenging storage conditions lead to the search for new forms of storage. Liquid organic hydrogen carriers (LOHCs) are positioned as a promising option to store hydrogen using a catalytic reversible reaction at moderate temperature. Notwithstanding, although reactor technology is the core section of the LOHC process, it has not been assessed yet. Therefore, in this work, a three-phase reactor analysis is performed including mass, heat, and momentum phenomena along with kinetics. In particular, the two most important reactors for three-phase reactions are evaluated, trickle bed and slurry. And two of the most attractive LOHCs systems, dybenzyltoluene and a mixture composed of 1,2-dimethylindole and 7-ethylindole, are considered. The influence of the operating and design variables was studied. The results show that, for hydrogenation slurry reactors, a first region may be formed where gas-liquid is the main resistance (60%-95%). It eventually ends up with a second one where kinetics becomes the controlling step. At this point, a better catalyst use is expected for the first region. Alternatively, trickle bed hydrogenation reactors are largely controlled by mass transfer over almost the whole reactor length. If the dehydrogenation process is assessed, kinetics resistance is predominant. Surrogate models are developed to optimize the reactor performance and to include the full reactor operation in futures process design analysis allowing for an effective deployment of LOHCs systems.

Automated summary

As renewable energy production increases, the demand for energy storage and carrier systems becomes crucial. Hydrogen, with its low volumetric energy density and challenging storage conditions, is positioned as a powerful tool for this purpose. Liquid organic hydrogen carriers (LOHCs) are considered a promising option for hydrogen storage, but the reactor technology for LOHC processes has not been thoroughly assessed. In this study, a three-phase reactor analysis is conducted to evaluate the two most important reactors for three-phase reactions, trickle bed and slurry. The influence of operating and design variables is studied for two attractive LOHC systems. The results show that the resistance in hydrogenation slurry reactors is mainly gas-liquid in the first region and eventually transitions to kinetics control in the second region. Trickle bed reactors, on the other hand, are primarily controlled by mass transfer. Surrogate models are developed to optimize reactor performance and facilitate the deployment of LOHC systems.