Overview of LOHC Technology Routes

What is "LOHC"

Liquid Organic Hydrogen Carriers Technology（ Abbreviated as“LOHC”）is a technology that uses reversible reactions between unsaturated organic liquids and hydrogen to store hydrogen, achieving hydrogen storage and transportation at ambient temperature and pressure in the form of saturated liquid compounds.

LOHC technology consists of two processes: hydrogen storage and hydrogen release. In the hydrogen storage process, hydrogen gas reacts with the hydrogen storage carrier (hydrogen-poor liquid) in the presence of a catalyst in the hydrogen storage reactor to produce a hydrogen-rich liquid, which is used for hydrogen storage and transportation. In the hydrogen release process, hydrogen gas is released from the hydrogen-rich liquid through the hydrogen release reactor under certain temperature conditions and catalytic action, simultaneously transforming the hydrogen-rich liquid back into a hydrogen-poor liquid, thus completing one cycle of hydrogen storage and release using organic liquids.

The LOHC technology can be traced back to 1975, when O. Sultan and M. Shaw first proposed using aromatic compounds such as toluene as hydrogen storage carriers to achieve reversible hydrogen storage, opening up new directions in hydrogen storage technology research. In 2020, Japan's Chiyoda Corporation used methylcyclohexane as a hydrogen storage carrier, transporting it by sea from Brunei to Kawasaki, Japan, marking the first long-distance hydrogen transport across the ocean. In Europe, a notable company is Germany's Hydrogenious Technologies, which has been dedicated to the research and development of LOHC technology since 2013. Their technology has been officially included in the European Commission's IPCEI "Green Hydrogen @Blue Danube" project, with plans to build a green hydrogen storage and release facility capable of storing and releasing 1,000 to 2,000 tons of green hydrogen per year in Europe. In green hydrogen projects in the Middle East, to transport green hydrogen from Oman to Europe, the project owners and technical partners will also use LOHC technology as the hydrogen storage carrier.

The technical route for LOHC

In principle, unsaturated compounds (organic molecules with carbon-carbon double or triple bonds) can absorb hydrogen during the hydrogenation process. However, good liquid hydrogen storage materials need to meet the following requirements: 1. Physicochemical stability and high safety; 2. High hydrogen storage density; 3. Efficient dehydrogenation and hydrogenation reactions with low energy consumption; 4. High cycle count and low degradation; 5. Easy availability of materials and low cost. Academic and industrial research has extensively studied and applied various organic liquid hydrogen storage materials, with the most commonly used organic liquid hydrogen storage material systems including: toluene, dibenzyltoluene, and N-ethylcarbazole materials. The dehydrogenation and hydrogenation reactions of these materials are shown in the following figure:

It can be seen that the hydrogen storage density of different hydrogen storage carriers has slight but not obvious differences, but there are significant differences in terms of safety, hydrogenation and dehydrogenation reaction conditions, and price. These characteristics will affect the competitiveness and applicability of different LOHC technology routes.

The advantages of LOHC

Compared to traditional hydrogen storage and transportation technologies, LOHC technology has the following characteristics and advantages:

◎ High hydrogen storage density, small footprint

The storage capacity of hydrogen in organic liquid storage per unit volume is significantly better than that of high-pressure gaseous hydrogen, and it is comparable to cryogenic liquid hydrogen (-253℃). In large-scale hydrogen storage scenarios (e.g., 600,000 Nm3), organic liquid hydrogen storage occupies only one-tenth the area compared to medium and low-pressure gas storage spheres. Additionally, due to its low marginal cost of storage, as the amount of stored hydrogen increases, the initial investment costs also become advantageous. LOHC also has the characteristic of scalability, allowing for an increase in storage capacity through the addition of more hydrogen storage liquid, even after the project is operational, at a low cost.

◎ Intrinsic safety

Hydrogen storage liquid can be stored and transported in a liquid state under normal temperature and pressure, with stable chemical properties, low volatility, non-flammable, non-explosive, non-toxic, and excellent safety performance. After evaluation by a third-party testing institution, it is classified as Class B fire hazard, with safety performance superior to fuel oil (diesel). In the case of large-scale hydrogen storage, it is not recognized as a major hazard source.

◎ Liquidness, convenient for large-scale storage and transportation

Liquid is the most suitable form for large-scale storage and transportation, and liquid hydrogen can be stored and transported using existing tanks, tank trucks, and pipelines, significantly reducing investment and costs in storage and transportation. A regular 30 cubic meter tank truck (non-hazardous chemicals) can transport 1.5 tons of hydrogen, which is 5-6 times the capacity of a 20Mpa gaseous tube trailer.

The value of LOHC

As a new type of hydrogen storage method, the LOHC technology can bring unique value to the current development of the hydrogen energy industry. For integrated green hydrogen chemical projects (such as producing green ammonia, methanol, aviation fuel, etc.), large-scale hydrogen storage is needed to bridge the fluctuating hydrogen production from renewable sources and the relatively stable hydrogen demand for chemical processes. Using LOHC technology can significantly reduce the safety risks of the project and improve inherent safety. At the same time, it allows for designing higher hydrogen storage capacities (which can be flexibly increased even after the project is operational), combined with reasonable gaseous hydrogen storage configurations, substantially reducing the proportion of grid electricity usage, increasing the final product yield, and effectively enhancing the overall economic viability of the project.

For hydrogen transportation, the reasonable range for gaseous hydrogen transport is only 50-100 kilometers. Based on the characteristics of organic liquid hydrogen storage allowing safe transport at normal temperature and pressure, hydrogen-rich liquids can be transported over long distances using ordinary carriers, reducing transport costs by 90%, and considering the conversion, the overall cost decreases by 50%. For hydrogen producers, the sales radius of hydrogen can be extended from 50 kilometers to a range of 500 kilometers. For hydrogen users, they can also obtain a more stable supply of hydrogen at lower costs.

Due to the bottlenecks in storage and transportation, the current production and consumption of hydrogen are more like widely distributed points, while the development of the hydrogen energy industry requires forming a large-scale network of hydrogen production and consumption across larger geographic areas. Safety, flexibility, and low cost are core requirements for future hydrogen storage and transportation technologies, which is where the significant value of LOHC technology lies.

For LOHC, the future is coming.