Swiss research intsitute Empa’s future mobility demonstrator, “move”, is investigating three paths for CO₂ reduction in road traffic—electric mobility, hydrogen mobility and synthetic fuels—against the background of a rapidly changing energy system.

All these concepts have advantages and drawbacks in terms of energy, operation and economics. In order to use them in a smart way, we need a deeper understanding of the overall system.

—Christian Bach, Head of Empa’s Automotive Powertrain Technologies lab

The latest project focuses on the production of synthetic methane from hydrogen and CO₂. Such fuels, produced synthetically with renewable energy, can be transported via conventional routes and made available through the existing infrastructure.

The basic chemical process of methanization has been known for more than 100 years as the Sabatier reaction. In “move”, another process developed further at Empa will be used—sorption-enhanced methanization. Empa researchers hope that this novel process engineering concept will lead to simpler process control, higher efficiency and better suitability for dynamic operation.

Methanization works by producing methane (CH₄) and water (H₂O) by catalytic conversion from carbon dioxide (CO₂) and hydrogen (H₂). Water causes problems with conventional processes, however; to remove it, serial methanization stages are typically required—with condensation areas in between. Due to the high reaction temperatures, a proportion of the water is converted back into hydrogen by the water-gas shift reaction. The gaseous product of the methanization reaction thus contains a few percent hydrogen, which prevents direct feeding into the gas grid; the hydrogen must first be removed.

CO₂ for the methanization as well as water for hydrogen production is taken directly from the atmosphere with a CO₂ collector from the ETH spin-off Climeworks. The system sucks in ambient air and CO₂ molecules remain attached to the filter. Using heat—around 100 °C—the CO₂ molecules can be released from the filter.

Empa researchers see further potential for optimization in the heat required for this CO₂ desorption.

Both hydrogen production and methanization continuously generate waste heat. By means of a clever heat management, we want to cover the heat requirements of the CO2 collector as much as possible with this waste heat

—Christian Bach

In addition to CO₂, the Climeworks plant also extracts water from ambient air, which is used for hydrogen production in the electrolysis device. This means that such plants are also conceivable in regions without water supply, for example in deserts.

In addition to new knowledge about technical and energetic aspects, insights about the economic efficiency of synthetic methane are one of the project’s prime goals. The project is supported by the Canton of Zurich, the ETH Board, Avenergy Suisse, Migros, Lidl Switzerland, Glattwerk, Armasuisse and Swisspower.

Currently, Bach’s team is concentrating on the investigation of water adsorption on porous materials and the process control of the catalytic reaction. Construction of the plant is planned for mid-2021.

Resources

• Kiefer F., Schröter K., Dimopoulos Eggenschwiler P., Bach C. (2021) “Significance of Synthetic Methane for Energy Storage and CO₂ Reduction in the Mobility Sector.” In: Bargende M., Reuss HC., Wagner A. (eds) 21. Internationales Stuttgarter Symposium. Proceedings. Springer Vieweg, Wiesbaden. doi: 10.1007/978-3-658-33521-2_6