At the project in Laufenburg, thanks to a new technology we are able to handle the production of e-diesel efficiently in compact units, making it more economical. The pilot facility offers scope for sector coupling, in other words combining the energy sectors power, heat and mobility, and makes it possible to store renewable energy.

—Reiner Mangold, Head of Sustainable Product Development at Audi

Audi e-diesel has the potential to make conventional combustion engines operate almost CO2-neutrally. To produce it, the power-to-liquid plant converts surplus hydropower into synthetic fuel. The green power generated on site in the hydroelectric power station produces hydrogen and oxygen from water by means of electrolysis.

This hydrogen, together with carbon dioxide, is converted in a two-step power-to-liquid process. First, the CO₂ and H₂ are converted into syngas in Ineratec’s RWGS (reverse water gas shift) reactor. In second step, the Fischer-Tropsch reactor produces Audi e-diesel and waxes—which are put to use in other areas of industry—from the syngas.

The Fischer-Tropsch products are free of aromatics and sulfur compounds. The CO₂ can be obtained from the atmosphere or from biogenous waste gases and, as with all Audi e-fuels, is the only source of carbon.

The core of Ineratec’s synthesis reactors is microstructured, thus providing a very large surface for heat and mass transport, thereby minimizing effects on reactor and catalyst performance. Highly exothermic reactions such as Fischer-Tropsch synthesis can be operated efficiently and safely in compact plants.

Ineratec says that its reactors are characterized by:

• Compact design due to the microstructure technology
• High syngas conversion per reactor pass and unique reactor productivity
• Excellent temperature control
• Short start-up and shut down times
• High load-flexibility
• Cost reduction for decentralized application

Audi and its partners plan to produce the first quantities of e-diesel in Laufenburg as early as next year. Audi and the project partner companies Ineratec and Energiedienst AG will submit the planning application for the facility in a few weeks’ time. Construction work is to begin in early 2018.

This is now Audi’s second partnership in a pilot facility that operates according to the power-to-liquid principle. Audi has already been working together with the energy technology corporation sunfire in Dresden since 2014.

There, sunfire is exploring the manufacturing of e-diesel based on the same principle, but involving different technologies. The other Audi e-fuels projects include its own power-to-gas facility in Werlte, north Germany, which makes Audi e-gas—i.e., synthetic methane—for the g-tron models A3, A4 and A5. The Ingolstadt carmaker is also researching the manufacture of e-gasoline together with specialist partners.