Chemical solutions towards carbon zero

The world’s greatest hope for reducing CO₂ emissions and mitigating the impacts of climate change lies in the transition to renewable energy, such as solar or wind power, but these cannot yet provide all of the power societies need.

Fuels that don’t produce CO₂ when they are burned could help fill the gap until renewables are more available. Hydrogen, either derived from fossil fuels, such as gas, or made from water using renewable power, is a great example.

Hydrogen molecules (H₂) chemically store a great deal of energy that is released when they are burned, with water as the only by-product. Hydrogen is also, in principle, readily available given that it is abundant in the form of water, which can be split in a sunlight-driven chemical reaction.

Hydrogen transport challenge

However, the challenge of how to safely and easily store and transport hydrogen has not yet been solved. It is a gas at room temperature, and can be cooled to a liquid at -253 °C for transport, but the costs can be prohibitive. The pressure also increases the possibility of leaks, which is dangerous given hydrogen’s high flammability.

Chiyoda Corporation, an engineering company headquartered in Yokohama, Japan, has been working on solutions to the problem of transporting hydrogen, as well other technology in support of net zero goals.

“The Chiyoda Corporation has been continuously developing innovative technologies in the fields of environment and energy since its founding in 1948,” explains Kenichi Imagawa, a research and development group leader at Chiyoda. “But now, we are shifting our accumulated expertise to global decarbonization and the realization of a net-zero society.”

Chiyoda has been developing a technology called SPERA Hydrogen™ to help with the transport issue, which takes advantage of so-called liquid organic hydrogen carriers (LOHC). The idea is to add hydrogen to an organic molecule, such as toluene, to create a ‘carrier’ molecule, methylcyclohexane (MCH). MCH is chemically stable and a liquid at normal temperature and pressure, making it much safer to handle and easier to transport than pure hydrogen.

“Taking advantage of this feature, hydrogen can be transported from areas where solar and wind resources are abundant, such as the Middle East, Africa, Australia and Latin America, to cities that consume large amounts of energy, located thousands of kilometres away,” says Imagawa.

Catalysts for change

A great advantage of Chiyoda's SPERA Hydrogen™ technology is that it is compatible with the existing transport infrastructure used for petrochemical products, such as tanks, chemical tankers and tanker trucks. This means that existing petroleum transport systems can be used, avoiding the problem of having to devise an entirely new hydrogen delivery infrastructure. Chiyoda hopes this will reduce costs and encourage the take-up of hydrogen as a low-carbon form of energy.

When the MCH reaches its destination, the hydrogen needs to be recovered. To optimize this process, so that the hydrogen can be used, Chiyoda has created long-lived catalytic materials based on its expertise in catalyst development. These provide more efficient dehydrogenation reactions.

And this industrial knowledge of catalysts is also aiding the production of another carbon-free fuel: ammonia. Again, ammonia can be burnt without creating CO₂ as a by-product, just water and nitrogen. It also has other opportunities for decarbonization similar to hydrogen.

The process of burning ammonia for energy could be achieved using today’s coal-fired power plants. “At a council of Japan’s Ministry of Economy, Trade and Industry it was estimated that if all major coal-fired power plants in Japan were to use 20% of their capacity to burn ammonia instead of coal, CO₂ emissions could be reduced by about 40 million tonnes,” says Ichiro Mizusawa, a senior adviser at Chiyoda.

The problem is that ammonia production as a fuel requires more energy. Chiyoda have partnered with academic and industrial teams to develop new catalysts for lower pressure and lower temperature ammonia synthesis as part of a project commissioned by Japan’s New Energy and Industrial Technology Development Organization (NEDO). Once the best catalyst is identified, Chiyoda is hoping to upscale its new ammonia synthesis process to industrial scales.

Reclaiming carbon

In addition to the work Chiyoda is doing to make hydrogen more useful and readily available as a fuel, they are also looking into other technologies to help mitigate the climate crisis and help societies and industries adapt on the path to carbon neutrality.

Among these are carbon capture technologies that can treat waste gas removed from natural-gas-fired power plants. There are many methods to achieve this, such as creating an absorbent material that works with relatively low concentrations of CO₂ — at present, many carbon capture technologies only work efficiently when there is a high concentration of CO₂.

The carbon recovered in this way can be stored underground, such as in depleted oil reservoirs, or at the bottom of the deep sea, held in place by high pressure. However, Chiyoda is now investigating whether the carbon can be recycled and used more productively. For example, it has developed a technology for combining the CO₂ with hydrogen to produce p-Xylene; a chemical that is a building block for polyester fibres and the resin used for plastic bottles.

Similarly, by passing CO₂ and water through their renewable-energy driven electrolysis technology, Chiyoda has been able to produce ethylene, a versatile chemical used in a wide range of industries, everywhere from producing plastics and glass to controlling the ripening of fruit and cutting metal.

These carbon capture and utilization schemes, together with non-carbon-based fuels will hopefully provide a useful stopgap while truly renewable energy sources are developed. More work needs to be done, but successful testing of technologies such as SPERA Hydrogen are all steps in the right direction.