Colorful hydrogen: What the color reveals about the origin

The world is looking to hydrogen; it is just as much in demand as an energy storage medium or fuel as it is for industrial processes, such as voestalpine’s future climate-friendly steel production (greentec steel). The “H2FUTURE” project launched at the Linz site proves that sustainable production of the gas is possible in large-scale continuous operation.

At voestalpine, hydrogen is produced in the most climate-friendly way: Using electrical energy from renewable sources, the pilot plant separates water into its components by electrolysis. This produces “green” hydrogen (H2) and the byproduct oxygen. At present, however, the vast majority (approx. 96%) of the world’s hydrogen demand of approx. 100 million t per year is met by steam reforming of natural gas, which produces ten times the amount of CO₂ for each cubic meter of H2. This process is also known as methane pyrolysis. In contrast, methane pyrolysis (Kværner process), a promising technology, produces solid carbon in addition to hydrogen. However, it also uses natural gas as a feedstock.

From water or natural gas, from nuclear power or fossil fuel – the origin and source materials of the electrical energy used as well as the color psychology determine the “color” of the hydrogen.

Because the gas, which is colorless by nature, has now become colorful. Our overview shows the breadth of the current spectrum:

• green hydrogen: Produced with regeneratively generated electrical energy by electrolysis of water.
• gray hydrogen: produced by steam reformation from fossil fuels; separated CO₂ is released into the atmosphere. (We also speak of gray hydrogen. when energy from fossil sources is used for electrolysis).
• Blue hydrogen: Generated like gray hydrogen; however, the captured CO₂ is stored (CCS: Carbon Capture and Storage) or processed (CCU: Carbon Capture and Usage).
• turquoise hydrogen: Produced by methane pyrolysis. Climate-neutral if the high-temperature reactor is operated with renewable energies and the resulting solid carbon is permanently bound.
• red/pink/purple, also brown hydrogen: produced by electrolysis, for which nuclear power is used.
• yellow hydrogen: produced by electrolysis with an energy mix of renewable and fossil sources.
• white hydrogen: By-product or waste product of other chemical processes, e.g. in the production of chlorine.

From the perspective of climate neutrality, all offerings that are not green would probably have to be blacklisted in the long term.

The idea of producing green hydrogen in regions that have reliable sustainable energy supplies, such as North Africa or the Middle East, sounds tempting. There would remain the question of transportation. Huge ships, such as the natural gas tankers with large pressure vessels, could be used. For this, however, the gas must be under high pressure and a great deal of energy is needed for compression – and the huge transport fleets would first have to be created.

Hydrogen pipelines are considered another option. But since hydrogen has a low density compared to other energy carriers (e.g., natural gas), enormously large quantities would have to be transported at high pressure. A corresponding quantity of pipelines would have to be kept available; how quickly trans- and intercontinental supply lines can become the plaything of geopolitical considerations is currently clearly demonstrated.