Audi has established a pilot plant in Germany that produces diesel fuel from water, carbon dioxide, and green electricity. The Dresden plant, which Audi developed in partnership with Climeworks and sunfire, opened Nov. 14.

The sunfire plant, which operates according to the power-to-liquid principle, requires carbon dioxide, water, and electricity as raw materials.The carbon dioxide is extracted directly from the ambient air using direct air capturing, a technology developed by Swiss partner Climeworks, according Audi.

In a separate process, an electrolysis unit powered with green electricity splits water into hydrogen and oxygen. The hydrogen is then reacted with the carbon dioxide in two chemical processes conducted at 220 degrees Celsius and a pressure of 25 bar to produce an energetic liquid, made up of hydrocarbon compounds, which is called Blue Crude. This process is up to 70 percent efficient, according to Audi.

As currently built, the pilot plant on the sunfire grounds in Dresden-Reic  k can produce approximately 160 liters of Blue Crude per day. Nearly 80 percent of that can be converted into synthetic diesel. This fuel (Audi e-diesel) is free of sulfur and aromatics. It also has a high cetane number, which means that it ignites very easily. Its chemical properties allow it to be blended in any ratio with fossil diesel. This means that it can be used as a drop-in fuel.

Audi is combining two technologies in this project, which is funded in part by the German Federal Ministry for Education and Research. The project was preceded by a two-year research and preparation phase to test carbon dioxide capturing from the ambient air and the power-to-liquid process for the production of synthetic fuel, according to the automaker.