Oxygen is one of the most abundant chemical elements on Earth and makes up 21 percent of the Earth's atmosphere. The gas, with the element symbol O, occurs naturally mostly as a diatomic molecule (O₂). This colorless, odorless gas is characterized by its high reactivity.
In electrolysis, water (H₂O) is broken down into its constituent parts. This process produces about eight kilograms of oxygen per kilogram of hydrogen. In fuel cells, this process is reversed: here, hydrogen reacts with oxygen to generate electrical energy. The only byproduct is pure water.
Industrial Extraction
The oxygen produced during electrolysis is increasingly evolving from a byproduct into a valuable raw material. Marketing this oxygen significantly improves the economic viability of electrolysis plants: According to calculations by the Fraunhofer Institute for Solar Energy Systems (ISE), the production costs for green hydrogen can drop by up to 45 percent if the oxygen is used commercially. The current market price for technical oxygen ranges from 65 to 120 euros per metric ton.
Today, conventional oxygen production is primarily carried out by separating air (rectification). The most important processes are the Linde and Claude processes. In these processes, air is first compressed, purified, and cooled to a very low temperature until the oxygen can be liquefied. For smaller quantities, pressure-swing adsorption is also used, in which nitrogen is bound to special molecular sieves.
Areas of Application
Industry has been using the gas for a long time in various sectors:
- Steel Production: Optimizing Combustion Processes in the Blast Furnace
- Medical Technology: Use in Ventilators and Oxygen Therapy
- Chemical Industry: Use as an oxidizing agent (a substance that facilitates chemical oxidation reactions)
- Wastewater Treatment: Supporting Biological Treatment in Wastewater Treatment Plants
- Fish Farming: Water Enrichment in Aquaculture
Handling and Safety
Handling oxygen requires special safety measures. As with hydrogen, there are two main options for transport and storage:
- Compression in gas cylinders or tanks (typically 200–300 bar)
- Liquefaction at minus 183 °C
Many users rely on on-site production to save on transportation costs. Strict safety regulations must be followed in this process, because:
- The gas greatly accelerates combustion processes
- Certain materials can become brittle
- Fats and oils can react explosively
In Germany, medical oxygen is subject to the German Medicines Act and must meet specific purity requirements.
Outlook
As the hydrogen economy expands, the importance of oxygen marketing will continue to grow. Major projects, such as hydrogen hubs, are integrating oxygen use into their plans. The combination of H2 and O2 production significantly improves the economic viability of electrolysis and can thus contribute to industrial decarbonization.
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