Liquid Organic Hydrogen Carriers and alternatives for international transport of renewable hydrogen

Abstract

Hydrogen can be transported over long distances when stored in Liquid Organic Hydrogen Carriers (LOHC). This transport is possible under the following conversion steps: first, hydrogen is stored inside a LOHC molecule (exothermic hydrogenation) at the starting point of the provision chain. Then, the loaded LOHC can be stored and transported. At the point of consumption, hydrogen is released (endothermic de-hydrogenation) and the unloaded LOHC returns to the point of hydrogen production. The optimal LOHC for transport should be liquid at ambient conditions and show similar properties to crude oil-based liquids (e.g., diesel, gasoline). This allows for a stepwise implementation using the existing crude oil-based infrastructure. However, there is a large variety of different LOHCs and other competing transport options; e.g., the transport of compressed hydrogen gas in pipelines or the transport of liquefied hydrogen in tanker ships. Against this background, this paper investigates the energy consumption and costs of these different hydrogen transport options. Therefore, the production of hydrogen is considered in areas with favorable renewable energy sources, followed by international transport logistics, and a local distribution in Germany. The assessment shows that the distance and the way heat is supplied to de-hydrogenate the LOHCs - especially for methanol - define the cost performance compared to a transport of compressed or liquid hydrogen. If the heat needed for dehydrogenation is covered by waste heat, dibenzyltoluene (DBT) or toluene can show benefits in terms of efficiency and costs. Furthermore, the different transport systems have different specific niches in which they are competitive; i.e., no specific transportation chain is superior to all systems under all circumstances. Nevertheless, the assessment shows that long-distance transport favors LOHC, while short-distance transport via pipelines can be used for lower costs.