Ammonia vs. dibenzyltoluene: A comparative assessment of hydrogen carriers

Technical comparison

Hydrogen storage capacity and energy density

Ammonia contains 17.8 % hydrogen by mass and approximately 121 kg H₂/m³ when liquefied at 8.6 bar or –33 °C1. This volumetric density is almost 30 % higher than LiqH₂ and roughly five times that of compressed hydrogen at 350 bar (~23 kg H₂/m³) 1. Because of its high hydrogen content and ease of liquefaction, ammonia offers a very high energy density (~3.83 MWh/m³) with boiloff losses of only approx. 0.025 % per day6. The LOHC DBT stores 6.2 wt % hydrogen with an energy content of 1.9 kWh/kg 3. The hydrogen rich form (perhydro-dibenzyltoluene) contains approximately 54 kg H₂/m³ (8) and remains liquid at ambient pressure, enabling storage and transport using conventional fuel infrastructure.

Reaction enthalpy and process conditions

Releasing hydrogen from the carrier requires energy. Ammonia is cracked by catalytic decomposition (NH₃ → 1.5 H₂ + 0.5 N₂). The theoretical minimum energy is 0.88 MWh/tNH₃ (5.0 MWh per ton H₂), while current crackers require 1.17–1.76 MWh/tNH₃ (6.63–9.97 MWh per ton H₂) at 700–900 °C6. In addition, downstream purification (e.g., removing residual ammonia) is often needed for fuel cell use. Hydrogenating DBT is exothermic (~9 kWh per kg H₂) while dehydrogenation requires approximately 11 kWh per kg H₂ at 250–320 °C8. The enthalpy difference is thus roughly 10 kWh/kg H₂ and heat integration is important for efficient operation4. The hydrogenation/dehydrogenation cycles can be repeated hundreds of times without significant degradation of the DBT carrier8. Laboratory studies show that aromatic carriers have hydrogenation enthalpies of 62–69 kJ mol⁻¹ H₂7, which are relatively high compared with heterocyclic LOHCs.

Physical properties and safety

Ammonia is a colorless gas that liquefies at –33 °C (1 bar) or 8.6 bar (20 °C) and has a pungent odor. It is toxic and corrosive; exposure limits are <25 ppm and high concentrations can be fatal. However, the chemical and fertilizer industries already handle large volumes (~190 Mt per year) and more than 180 ammonia terminals exist worldwide2.

In the other hand, DBT is an oil like liquid with a melting point around –34 °C and a boiling point ~390 °C3. Both the lean (DBT) and H2 rich (perhydro-dibenzyltoluene) forms have flash points above 110 °C, making them hardly flammable and nonexplosive even when loaded with hydrogen8. The LOHC is classified as a “substance of high concern” because dibenzyltoluene may contain benzene7. Moreover, the hydrogen rich DBT is more viscous than diesel; mixing with benzyltoluene lowers viscosity, but pipeline transport is impacted1.

Carrier recyclability and byproducts

Ammonia cracking produces nitrogen as the only byproduct and does not require carrier return. The DBT system operates as a closed loop: hydrogen lean DBT must be shipped back for reuse. Dehydrogenation of DBT proceeds through partially hydrogenated intermediates; conversion can reach ~97 % at 250–320 °C1. However, incomplete dehydrogenation generates mixtures and potential formation of benzene and other aromatics1. Catalysts (often precious metals) are required to achieve acceptable kinetics for both hydrogenation and dehydrogenation. Although hundreds of cycles are claimed, catalyst deactivation and carrier degradation remain technical challenges.

Commercial and logistics comparison

Infrastructure and market maturity

Ammonia is the second most produced chemical and is traded worldwide for fertilizer production. Approximately 190 Mt are manufactured annually (16), and more production is coming online. Existing liquefied petroleum gas (LPG) infrastructure can be converted to handle ammonia2. Conversely, DBT based LOHC technology is at pilot scale. Hydrogenious LOHC Technologies operates a plant in Erlangen, Germany and is developing a hydrogen release hub capable of delivering 1,800 t H₂ per year by 2028 and an industrial storage facility (Project Hector) for byproduct hydrogen at CHEMPARK Dormagen8. A real-world demonstration transported over 100 t of hydrogen via methylcyclohexane (toluene system) from Brunei to Japan over ten months, but similar largescale shipments with DBT have yet to occur.

Costs and economic drivers

Carrier cost is a critical factor. Aromatic compounds such as benzene and toluene are commodities produced in tens of millions of tons per year and cost <1 € kg⁻¹ ⁽⁷⁾. However, dibenzyltoluene costs roughly ten times more than toluene; hydrogen lean DBT has been reported at €2–4 kg⁻¹ ⁽³⁾ or approximately €4–5 per liter. Each cubic meter of DBT carries about 54 kg of hydrogen, implying a carrier cost of ~€0.07–0.09 per kilogram of hydrogen transported (excluding capital and operation). Ammonia, by contrast, is mass produced and its price generally tracks natural gas; the cost of storing hydrogen in ammonia has been estimated at ~0.54 US$/kg H₂ for 182day storage compared with ~15 US$/kg H₂ for pure hydrogen storage⁵. Although energy is consumed in cracking, the additional cost is lower than the energy penalties associated with cryogenic hydrogen. The U.S. Department of Energy’s 2024 infrastructure plan targets a delivered hydrogen cost of ≤$7 kg⁻¹ by 2030 with an ultimate goal of $4/kg ⁸. Operational costs for LOHC systems are dominated by dehydrogenation. A recent technoeconomic analysis found that the dehydrogenation unit and the initial carrier loading are the most impactful cost items; DBT’s high price significantly affects levelized transport cost. The same study noted that hydrogenation enthalpy and carrier cost are key parameters for LOHC selection. Because DBT must be shipped back empty, the roundtrip transport distance and vessel utilization strongly influence the cost per kilogram of hydrogen.

Logistics and handling

Ammonia can be liquefied by cooling to –33 °C or pressurizing above 7.5 bar and is routinely stored in large tanks with minimal boil ‑off ⁶. The gas is toxic and corrosive, so pipelines and tankers must be designed with appropriate materials and safety systems. Nevertheless, existing LPG infrastructure can be repurposed, and global trade networks already exist. Cracking ammonia at the point of use requires high temperatures and may require purification to meet fuel cell tolerances. In contrast, DBT behaves like a ‑heat transfer‑ oil: it is liquid at ambient conditions, non‑explosive and has a flash point of 112.5 °C ⁸. The loaded carrier can be transported in standard tanker trucks or barges. There is no boiloff or ‑self-discharge and the LOHC can be stored for months. However, the high viscosity of ‑hydrogen rich‑ DBT and its classification as a hazardous substance limit pipeline use and require specialized handling. Logistics must also account for the return of the spent carrier to the hydrogenation plant, doubling the number of voyages compared with ammonia.

Discussion: tradeoffs between ammonia and DBT

Ammonia offers a high hydrogen density and benefits from mature global infrastructure. It can be stored and transported economically using existing LPG or ammonia terminals, and it does not require return shipping of a carrier. The main drawbacks are its toxicity, corrosiveness and the need for high temperature cracking. Nitrogen byproduct must be vented or captured. Emerging distributed cracking technologies may reduce the energy needs, but purity requirements for proton exchange membrane (PEM) fuel cells remain challenging⁶.

DBT based LOHC systems provide safer handling; the carrier is nonflammable, nonexplosive and has no vapor pressure at ambient conditions. The system utilizes existing liquid fuel infrastructure and does not require cryogenic temperatures or high pressure. However, the hydrogen storage capacity is lower than ammonia, and dehydrogenation consumes significant energy at 250–320 °C. The need to transport the dehydrogenated carrier back to the point of hydrogenation doubles the logistics effort. Moreover, the high cost of the DBT carrier and the potential formation of benzene during dehydrogenation are current barriers to largescale adoption⁷. Catalytic and process innovations aimed at reducing dehydrogenation enthalpy and carrier price could make LOHCs more competitive.

Conclusion

Ammonia and DBT represent two contrasting strategies for transporting hydrogen. Ammonia leverages a century of industrial experience and provides high energy density and low storage cost but suffers from toxicity and cracking energy penalties. DBT based LOHCs offer safer handling and compatibility with liquid fuel logistics but have lower hydrogen content, require energy intensive dehydrogenation and entail the additional cost of returning the carrier. Continued research into catalysts, heat integration and carrier formulation, combined with declining renewable power costs, will determine the future roles of these carriers in the hydrogen economy.

Figures

Figure 1 illustrates the volumetric hydrogen storage density of selected carriers. The chart shows that liquid ammonia achieves the highest hydrogen density (~121 kg H₂ m⁻³), followed by liquid hydrogen (~71 kg H₂ m⁻³), DBT LOHC (~54 kg H₂ m⁻³) and compressed hydrogen at 350 bar (~23 kg H₂ m⁻³). These differences directly influence storage vessel size and transportation efficiency.

1. Scale economies vs. modular flexibility.

At small scale, ammonia’s high capital cost per unit output makes it uneconomical, while modular LOHC systems can be deployed cheaply using standard reactor and liquid-handling equipment. At large scale, economies of scale and existing global ammonia infrastructure lower unit costs, making ammonia more cost-effective for high-volume transport than LOHC.

2. Hydrogen density and freight.

Ammonia’s gravimetric hydrogen content (17.8 wt %) and volumetric density (121 kg H₂ m⁻³) are about three times those of dibenzyltoluene. This means fewer ship voyages and smaller storage tanks per kilogram of hydrogen transported, lowering freight costs in the largescale model. In the small-scale model these savings are less significant, so the LOHC’s safety and ease of handling outweigh the density advantage.

3. Energy consumption.

Dehydrogenating LOHCs such as dibenzyltoluene requires ~11 kWh of thermal energy per kilogram of hydrogen, whereas cracking ammonia needs ~9 kWh per kg. At large scale, the cumulative energy savings favour ammonia; at small scale the difference is modest and LOHC’s lower CAPEX may dominate.

4. Product value.

The largescale model assumes ammonia derived hydrogen can be sold at a higher price because ammonia can be converted into fertiliser or used directly as a fuel. The small-scale model uses a lower selling price appropriate for hydrogen sold at retail via LOHC dehydrogenation. The revenue differential substantially improves the ammonia option’s profitability in the largescale scenario.

5. Carrier return.

LOHC systems must ship the hydrogen lean carrier back to the source for rehydrogenation, adding logistics and carrier makeup costs. Ammonia cracking releases nitrogen and hydrogen, so no carrier returns are needed, which becomes a significant advantage for large distances in the ammonia favouring model.

In essence, LOHCs are attractive for smaller, distributed applications where safe handling, modular deployment and lower capital cost are paramount; ammonia becomes attractive for large volume, long distance transport, where its high hydrogen density, established industrial network and lack of carrier return drive down per kilogram costs.

References

1. RIVM “Liquid Hydrogen Carriers” report (2023) – provides gravimetric and volumetric hydrogen densities, boiling points, and melt points for ammonia and multiple LOHCs.
2. protonventures.com- Proton Ventures opinion article on ammonia (2023) – supplies data on annual ammonia production, terminal infrastructure, hydrogen content and maturity of green ammonia projects.
3. arpa-e.energy.gov - Hydrogenious.net LOHC Technologies brochure (2024) – describes the physical properties of dibenzyltoluene, including hydrogen storage density, reaction energetics, flash point, safety features and ongoing commercial projects such as the Green Hydrogen@Blue Danube hub.
4. Hysafe report on liquid organic hydrogen carriers – summarises energy requirements for hydrogenation/dehydrogenation and compares LOHCs like benzyltoluene and ‑N‑ethylcarbazole.
5. ammoniaenergy.org- Ammonia Energy Association article (2019) – discusses ammonia’s liquefaction conditions, storage costs and relative volumetric energy density compared with liquid hydrogen.
6. Kleinman Center for Energy Policy digest on ammonia (2020) – details energy requirements for ammonia synthesis and cracking, boiloff rates and energy density.
7. re.public.polimi.it - Spatolisano et al. “Assessing opportunities and weaknesses of green hydrogen transport via LOHC” (2024) – provides technoeconomic analysis of LOHC systems, highlighting that dibenzyltoluene costs roughly ten times more than toluene and that dehydrogenation and carrier cost dominate levelized transport cost.
8. hydrogenious.net Hydrogen Infrastructure Technologies Subprogram overview (U.S. DOE, 2024) – outlines cost targets for delivered hydrogen, emphasizing the need to reach ≤$7/kg H₂ by 2030.