Institute for Micro Process Engineering (IMVT)

Kopernikus Project: Power-to-X Research Cluster B1 Hydrogen Carriers

How do we want to achieve the turnaround in mobility? There is hardly a way around hydrogen as an energy carrier. This project deals with the issues surrounding the storage, transport and provision of hydrogen.

Background

As part of the energy transition, excess energy from fluctuating energy sources such as wind and solar energy schould be stored and then made available independently of the location, time and according to the demand. The excess electrical energy is converted with a high degree of efficiency via electrolysis into chemical energy in the form of hydrogen with a particularly high gravimetric energy density (33 kWhth/kgH2). However, storage proves to be a major challenge due to the low volumetric energy density (0.003 kWhth/LH2 at 25°C and 1 atm). Common solutions such as pressurized hydrogen at 350 or 700 bar (0.8 or 1.3 kWhth/LH2) and liquid hydrogen (2.4 kWhth/LH2) can only partially remedy this situation due to their high hazard potential and difficult handling.

The idea of liquid organic hydrogen carriers (LOHC)

An alternative technology being investigated in the Kopernikus project: Power-to-X is the storage of hydrogen in a so-called liquid organic hydrogen carrier (LOHC). By reversible hydrogenation, the LOHC is loaded with hydrogen (LOHC+) or discharged (LOHC-). The LOHC serves as a kind of "returnable bottle".

Chemical realization

The LOHC is loaded/unloaded only under certain conditions (pressure, temperature) and in the presence of a catalyst. In the scenario of a decentralized application, requirements such as compactness, scalability and dynamics with a constant high volume and catalyst-related hydrogen release rate are placed on the release unit. At the same time, the impurities produced during the reaction have to be minimized in order to ensure a high cyclicality of the LOHC and to provide the hydrogen in the purest possible form for further applications.

Micor Process Engineering

The use of microstructures in process engineering makes it possible to intensify the transport of materials and heat as well as surface-determined phenomena and thus to intensify entire processes. In practice, this enables almost isothermal operating conditions to be created and the regulation and control of individual processes to be improved. The modular design allows a wide range of product capacities to be covered.

The system perhydro-dibenzyltoluene/dibenzyltoluene (multi phase reaction)

The system perhydro-dibenzyltoluene (18H-DBT, LOHC+) /dibenzyltoluene (0H-DBT, LOHC-) proves to be a promising LOHC. In addition to a storage density of 62 gH2/kgLOHC+ (equivalent to 2.1 kWhH2/kgLOHC+), the LOHC is easy to store due to its high stability under atmospheric conditions. In addition, the material system is flame-retardant, non-explosive and non-toxic and therefore not classified as hazardous material. This results in lucrative opportunities to use the existing infrastructure via tanker trucks for the distribution of the LOHC.

 

 

Reactor concept for the dehydrogenation of perhydro-dibenzyltoluene

A so-called circular reactor is used to release the hydrogen from the LOHC. Under reaction conditions, the LOHC+ remains liquid, while the catalyst (in the liquid) is subject to increased bubble formation. The microstructure, in which the flow is radially directed outwards, can counteract the increase in volume caused by the progressive gas production and simplifies the discharge of the gas from the multiphase flow.

The system perhydro-benzyltoluol/benzyltoluene (gas phase reaction)

The system perhydro-benzyltoluene (12H-BT, LOHC+) /benzyltoluene (0H-BT, LOHC-) is also proving to be a promising LOHC. In addition to a storage density of 62gH2/kgLOHC+ (corresponds to 2.1 kWhH2/kgLOHC+), the LOHC is easy to store due to its high stability under atmospheric conditions. In addition, the material system is flame-retardant and non-explosive and is therefore not classified as hazardous material. This results in lucrative opportunities to use the existing infrastructure via tanker trucks for the distribution of the LOHC.

 

Reactor concept for the dehydrogenation of perhydro-benzyltolene

A microstructured membrane reactor is used to release the hydrogen from the LOHC. On the reaction side there is a fixed catalyst bed with bars, while on the separation side microchannels ensure that the hydrogen is removed. A mechanically stabilized metallic membrane (Pd/PdAg with 5-16 µm thickness) is welded between the microstructures, which separates the hydrogen from the product mixture in high purity.