(49h) Hydrodynamic Challenges of Heat Transport in a Catalytic Multiphase Dehydrogenation Reactor

Liquid organic hydrogen carriers (LOHC) are an attractive option for the storage and global distribution of regeneratively produced hydrogen. The release of hydrogen takes place in an endothermal reaction and is typically carried out in tubular fixed bed reactors. This contribution deals with the dehydrogenation of the loaded carrier species perhydro-benzyltoluene (H12-BT) and perhydro-dibenzyltoluene (H18-DBT). As the reaction is accompanied by a strong volume expansion (up to factor 670) and evaporation of LOHC, the system is characterized by complex hydrodynamic conditions that change continuously along the reactor axis [1].

To support the understanding of this multiphase reactor and to specify its local transport properties, we have performed heat transport measurements under reactive conditions. Dehydrogenation reactions with H12-BT and H18-DBT were carried out in one single vertical tube that was equipped with high-resolution temperature measurement. The experimental data was analyzed using a model that balances heat consumption in the reactor and thus enables the examination of thermal parameters and fluid dynamic properties. The results reveal that the two carrier systems differ significantly in their temperature behavior and this difference is strongly connected to the degree of evaporation in the system. As dehydrogenation of H12-BT predominantly takes place in the gas phase, thermal parameters are generally lower compared to H18-DBT. Based on the results, two main regimes for the system can be identified: 1) When LOHC is primarily in the liquid phase, heat input is dominated by the reaction. 2) As vapor proportion and accordingly heat transfer resistance increases, the regime transitions to a state where heat input is mainly dominated by evaporation. This knowledge generally contributes to a better understanding of the hydrodynamic challenges in the dehydrogenation reactor and supports the development of more efficient configurations.

[1] Willer et al., Int. Journal of Hydrogen Energy 57, 1513-1523, 2024