Verfahrenstechnische Betrachtung und Optimierung der Freisetzung von Wasserstoff aus organischen Trägermaterialien

Liquid Organic Hydrogen Carriers (LOHC) are able to store hydrogen with a high volumetric density of up to 57 g(H2)⁄l(LOHC). Coupled with an eleyctrolyzer and a fuel cell those can be also used as an electrical storage system. To compensate regional differences in supply and demand of energy LOHCs can be distributed by naval shipment and pipeline transportation. The energy demand for the distribution of dibenzyl toluene was modeled for a pipeline transport over a distance of 400 km. Results show an energy demand of 1 % of the stored energy for forward and backward transportation. The hydrogenated dibenzyl toluene has to be heated up to at least 25 °C to use current pipeline systems due to high viscosity. During the dehydrogenation reaction thermal energy is needed to release hydrogen. This may be supplied by internally produced hydrogen, using a hydrogen burner, or external sources like natural gas or high temperature industrial heat. For example the waste heat of a cement plant is sufficient to completely cover the thermal energy demand of the LOHC system if coupled with a thermal energy storage system. In case of using a hydrogen burner the efficiency as an electrical storage system is at maximum 16.5 % (without heat coupling), respectively 31.2 % (additionally supply of domestic heat). By optimizing the complete hydrogen release system energetically, the best operation point in the dehydrogenation reaction is about 300 °C and 2 bar. Using a natural gas burner coupled with compressed hydrogen storage, the optimal operation range is a temperature from 340 to 350 °C and a pressure from 5 to 6 bar. During the dehydrogenation reaction dibenzyl toluene is partly or completely vaporized. The share of vaporization is modeled and examined experimentally. If the liquid reactant is completely in contact with the catalyst, the share of vaporization is close to the thermodynamically calculated one. At 300 °C, 1 bar and for conversion rates above 50 % completely vaporization is expected. To provide purified hydrogen, an activated carbon adsorber is very effective to separate the cyclic compounds from hydrogen. In case of a highly pure hydrogen requirement a palladium membrane shall be used, which decreases the efficiency of the LOHC system by 10 % relatively. The current infrastructure can be used for transportation of monobenzyl toluene. However, dibenzyl toluene as a LOHC can reach higher efficiencies.