By Dr. Peter Gless, Senior Business Development Manager, Hydrogenious LOHC Technologies
Today, and even more so in the future, many countries will depend on hydrogen imports to meet their huge demand in the energy, mobility, and industrial sectors. Green hydrogen, produced from renewable energy sources such as solar and wind, is particularly essential to drive the decarbonization of these sectors.
Unfortunately, not all countries have the capacity to produce renewable energy and green hydrogen in the quantities required, making long-distance transport even more critical to establishing a global hydrogen economy. At the same time, the properties of molecular hydrogen make it a very difficult commodity to store and transport, as it is extremely volatile and even explosive. The question of which technology can ‘tame’ this particular energy source and allow for its safe and cost-efficient transport and storage is of utmost importance.
Non-pipeline methods for hydrogen transport, such as in the form of GH2, LH2, ammonia or bound to an LOHC are usually easier to scale, faster to implement and more flexible when faced with challenging transport conditions, while pipeline-based transport is expected to be more cost-efficient in the long term, but also has unique challenges to deal with.
However, the LOHC technology based on benzyl toluene stands out among the other hydrogen transport technologies, not only in terms of safety, flexibility, and cost efficiency, but also when examining possible synergies with industrial off-takers.
Hydrogen transport with LOHC
LOHCs are organic carrier liquids that can chemically bind hydrogen (hydrogenation) and release it again when needed (dehydrogenation). Stored in the LOHC, the hydrogen can be transported much more easily and safely to its destination. After the hydrogen is released from the LOHC, the carrier material is not consumed but instead shipped back to the hydrogen production site and re-used for the next hydrogen transport.
There are several possible LOHCs, such as carbazole, toluene/methylcyclohexane (MCH), dibenzyl toluene or benzyl toluene. The latter has particularly positive properties as a hydrogen carrier, since it is a non-explosive, flame-retardant thermal oil with a lower hazard potential than diesel, is already well established in the industry as a heat conductor oil and is also very stable compared to other LOHCs.
LOHC based on benzyl toluene (LOHC-BT) does not require low temperatures or high pressure and can be transported over long distances in the existing liquid fuel infrastructure. It also shows no boil-off (hydrogen losses), not even during long periods of time. Hydrogen purity according to ISO-14687 is ensured. By using the existing infrastructure, LOHC-BT is also particularly fast and cost-effective to implement, and the local workforce for handling of liquid fuels can be leveraged, which in turn helps securing jobs. The flexibility of the technology favours diversification of import routes – transport via tank ships, barges, railroad and tanker trucks is possible.
Especially when seaports and barge ports are involved as transshipment points for the onward transport of hydrogen to off-takers, the LOHC-BT is advantageous due to its relatively low hazard potential compared to, for example, the highly toxic ammonia, which is considered to be very problematic in the urban environment of ports close to cities such as Amsterdam, Rotterdam or Hamburg.
Benefits of LOHC for industrial applications
An advantageous characteristic of the LOHC-BT technology lies in the chemical process itself: while the hydrogenation (storage of hydrogen in the LOHC) is an exothermic process that produces excess heat energy, the dehydrogenation (release of hydrogen from the LOHC) is an endothermic process – it requires additional energy in the form of heat.
This opens up synergies on the hydrogen production side, where the excess heat from hydrogenation could for example be fed into local heat grids or used for seawater desalination. On the off-taker side, heavy industry with a lot of process heat could leverage this excess energy for the dehydrogenation of the hydrogen from the LOHC-BT.
Steel mills are among the industry off-takers that can particularly benefit from the LOHC-BT technology: they not only need green hydrogen as a form of carbon-neutral energy source but also molecular hydrogen with high purity for their production processes. LOHC-BT can easily be stored at the off-taker site for releasing hydrogen on demand, which is key for industrial use. Steel mills also have a lot of excess heat that could be integrated in the LOHC-BT dehydrogenation process, lowering the total cost of ownership.
Hydrogen transport technologies compared
When comparing different hydrogen transport technologies, it quickly becomes clear that there is no one perfect solution for all applications. Since each transport technology has specific advantages and disadvantages depending on the application, an agnostic approach in terms of technologies is essential. In addition to the above-mentioned LOHC technology, several solutions are currently in focus of the public discussion.
Compressed hydrogen (CH2) stored in suitable pressure vessels (e.g., pressure cylinders) is already widely used today as a transport technology as well as for mobility. However, it is only cost-effective for very short distances, and the energy input for compression is relatively high, making it unsuitable for international import/export on an industrial scale.
Hydrogen liquefied at -253°C (LH2) has a high storage density, is being researched intensively and is already being used in some areas (e.g., automotive and aerospace industries). However, the considerable energy input and high technical expenditure for liquefaction, storage and transport are a challenge, especially for large-scale transport over long distances. LH2 requires complex infrastructure and costly thermal insulation. At the same time, boil-off, i.e., evaporation of hydrogen during transfer and storage, is difficult to avoid.
Ammonia (NH3) is used in large quantities in the fertilizer industry. In the future, green hydrogen can be stored in the form of NH3 and then transported on ocean-going ships approved for chemicals. After transport, the hydrogen molecule can be separated from NH3 by means of cracking.
However, due to its high toxicity and corrosive properties, ammonia is a very hazardous substance that can only be transported and stored with considerable effort and cost. Long-distance transport of hydrogen in the form of NH3 to end users is thus made much more difficult. Separating hydrogen from NH3 also requires a lot of energy at high temperatures, and the cracking technology needed for separation does not yet exist on a large industrial scale. The released hydrogen would also have to be extensively processed to obtain corresponding degrees of purity.
Pipeline-based transport of gaseous, compressed hydrogen makes it possible to transport a large amount of energy relatively safely. For this purpose, either new pipelines must be built, or existing natural gas pipelines must be upgraded. The construction of new pipelines is accompanied by very high investments and a tendency towards negative social acceptance. Converting existing natural gas pipelines must be examined for each individual case. The availability of the necessary compressors for large-scale hydrogen transport is still being researched, and the connection of new consumers is not always possible.
The construction of a European ‘hydrogen backbone’ with mainly converted natural gas pipelines for example can advance a Europe-wide connection of hydrogen sources and consumers at a very low cost. However, it can only cover part of the projected transport demand for Europe, as not all sources and consumers can be linked without building new pipelines.
Since the global transformation of energy systems as well as decarbonization of industry and mobility will require the export and import of cost-efficient, green hydrogen, a reliable and safe transport infrastructure for industrial volumes of hydrogen is a key factor for success. All the above-mentioned transport technologies will play their part in ramping up a global hydrogen economy and must be considered in the short and long term. LOHC-BT is one of these very promising solutions that offers a lot of benefits in terms of safety, handling, and flexibility. Its synergy with potential industrial off-takers that have a lot of excess heat energy, such as steel mills, underscores the importance of considering different hydrogen transport technologies on a case-by-case basis, in order to maximize the inherent advantages of each technology.