Liquid Organic Hydrogen Carriers (LOHCs) represent a promising solution for hydrogen export, offering a balance between safety, energy density, and compatibility with existing infrastructure. Unlike compressed or liquefied hydrogen, LOHCs store hydrogen chemically within organic compounds, enabling transport at ambient conditions. This method avoids the extreme temperatures or pressures required for alternatives like liquid hydrogen (LH2) or ammonia, making it particularly attractive for long-distance hydrogen trade.
LOHCs are typically aromatic or cyclic compounds that undergo hydrogenation and dehydrogenation reactions. Common carriers include toluene, dibenzyltoluene, and N-ethylcarbazole. These compounds are hydrogenated at the export site, binding hydrogen molecules to their chemical structure. The resulting hydrogen-rich LOHC is then transported via conventional tankers or pipelines. At the destination, the hydrogen is released through dehydrogenation, and the depleted carrier is returned for reuse. This closed-loop system minimizes waste and reduces the need for fresh feedstock.
The hydrogenation and dehydrogenation processes require catalysts and heat. Hydrogenation is exothermic, often operating at temperatures between 100-200°C and pressures of 30-50 bar, depending on the carrier. Dehydrogenation is endothermic, typically needing temperatures of 250-300°C and lower pressures. The energy efficiency of the cycle depends on the carrier’s properties and the process design. For example, dibenzyltoluene has a hydrogen storage capacity of around 6.2 wt%, while N-ethylcarbazole can reach up to 5.8 wt%. The energy penalty for hydrogen release ranges from 25-35% of the stored energy, comparable to ammonia cracking but higher than LH2 evaporation.
Transport logistics for LOHCs leverage existing liquid fuel infrastructure. The carriers are non-toxic, non-flammable in their hydrogenated state, and stable under ambient conditions, eliminating the need for cryogenic tanks or high-pressure vessels. This simplifies shipping, as LOHCs can be handled like diesel or crude oil. Tanker ships, railcars, and trucks can all be used without significant modifications. The ability to use standard ports and storage facilities reduces capital expenditure, a key advantage over LH2, which requires specialized cryogenic terminals.
Comparing LOHCs to other hydrogen carriers reveals trade-offs in energy efficiency and infrastructure needs. Ammonia has a higher hydrogen density (17.6 wt%) but requires energy-intensive synthesis (Haber-Bosch process) and cracking (600-700°C). It also poses toxicity risks and demands corrosion-resistant materials. Liquid hydrogen offers high purity but suffers from boil-off losses (0.5-1% per day) and requires energy-intensive liquefaction (30-40% of stored energy). LOHCs avoid these issues but have lower hydrogen density and require dehydrogenation units at import sites.
Pilot projects demonstrate the commercial potential of LOHCs. In Germany, the Hydrogenious LOHC Technologies project has successfully deployed dibenzyltoluene-based systems for hydrogen storage and transport. Japan’s Chiyoda Corporation developed the SPERA Hydrogen system, using methylcyclohexane as a carrier, with a demonstration project in Brunei exporting hydrogen to Japan. These initiatives highlight the scalability of LOHC systems, with capacities ranging from small-scale demonstrations to industrial-level applications.
Commercial viability hinges on several factors. LOHCs benefit from lower transport costs compared to LH2 or ammonia, as they avoid specialized infrastructure. However, the dehydrogenation step adds complexity and cost at the import site. The round-trip efficiency of LOHC systems (60-70%) is competitive with ammonia (50-60%) but trails LH2 (70-80%). The choice of carrier depends on regional infrastructure, end-use requirements, and energy prices. For regions with established liquid fuel networks, LOHCs offer a pragmatic transition pathway.
Energy efficiency across the supply chain varies significantly. A breakdown of key metrics:
- LOHCs: 6-7% wt hydrogen, 25-35% energy penalty for release.
- Ammonia: 17.6% wt hydrogen, 20-30% energy penalty for cracking.
- LH2: 100% wt hydrogen, 30-40% energy penalty for liquefaction.
Infrastructure needs also differ:
- LOHCs: Minimal modifications to liquid fuel infrastructure.
- Ammonia: Requires synthesis plants, cracking units, and toxic handling protocols.
- LH2: Demands cryogenic storage and transport systems.
Despite the advantages, challenges remain for LOHCs. The dehydrogenation process requires heat, often sourced from fossil fuels, though renewable integration is possible. Catalyst durability and cost are ongoing concerns, with research focused on improving longevity and reducing precious metal usage. The closed-loop system’s efficiency depends on the carrier’s stability over multiple cycles, with degradation being a limiting factor.
Looking ahead, LOHCs are likely to play a significant role in hydrogen export, particularly for regions prioritizing safety and infrastructure reuse. Their compatibility with existing systems provides a lower-barrier entry into the hydrogen economy, while ongoing research aims to improve efficiency and reduce costs. As pilot projects scale and technology matures, LOHCs could become a cornerstone of global hydrogen trade, complementing other carriers like ammonia and LH2 in a diversified energy landscape.