Organics Challenge Ammonia as Hydrogen Carriers

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For 8 months in 2020, the Japanese engineering firm Chiyoda conducted an ambitious demonstration. At a natural gas processing plant in Brunei, toluene molecules were saturated with hydrogen to form methylcyclohexane (MCH).

Container ships carried tanks of the liquid 5,000 km to Kawasaki, Japan. There, a Chiyoda-designed plant heated the MCH to more than 350 °C over a proprietary catalyst, dehydrogenating it back into toluene. A local refiner, TOA Oil, used the resulting hydrogen to power a gas turbine; Chiyoda shipped the spent toluene back to Brunei to start the process all over again.

LOHCs

Chiyoda and its Japanese partners involved in the project ferried 102 metric tons (t) of hydrogen to Japan during this demonstration. The company proved the concept again in 2022 using larger chemical tankers.

“This was also a success, so that means we are ready for commercialization,” says Osamu Ikeda, a business development manager at Chiyoda. The firm envisions establishing a vast network connecting hydrogen-producing locales like the Middle East, North America, and Australia with consumers in Japan, Singapore, western Europe, and other places with an appetite for clean energy.

The idea of liquid organic hydrogen carriers (LOHCs) like the MCH-toluene system is hardly new. It has been obvious to chemists for decades that they could load cyclic and heterocyclic compounds with hydrogen for storage and transport.

In 1986, scientists from Italy’s Institute CNR for the Transformation and Storage of Energy wrote a prescient piece in Precious Metals Review about the potential of “MTH”—their term for the MCH-toluene-hydrogen cycle. The authors “hoped that in time, as fossil fuels are increasingly depleted, the needs of the hydrogen economy will match the prospects offered by the MTH process, like a cure in search of a disease.”

The time these scientists foresaw may have arrived, albeit with climate change rather than fossil fuel scarcity as the ailment. Governments and industry are looking for safe and economical ways to ship green hydrogen over great distances.

Companies such as Chiyoda and the Japanese refiner Eneos see their moment and are clearing final technical hurdles for MCH. A German start-up, Hydrogenious LOHC Technologies, is scaling up a benzyl toluene–based system. Compounds like N-ethylcarbazole might also emerge as commercial hydrogen carriers.

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Source: CEN

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