Creating diesel fuel from air and water

Audi is making a new fuel for internal combustion engines - a synthetic diesel that is made from just water and carbon dioxide. The company's pilot plant, which is operated by German startup Sunfire in Dresden, produced its first batches of the "e-diesel" in April 2015. The base fuel is referred to as "blue crude," and begins by taking electricity from renewable sources like wind, solar or hydropower and using it to produce hydrogen from water via reversible electrolysis. The hydrogen is then mixed with CO2 that has been converted into CO in two chemical processes, and the resulting reactions produce a liquid made from long-chain hydrocarbons - this is blue crude, which is then refined to create the end product, the synthetic e-diesel.

Audi says that the carbon dioxide used in the process is currently supplied by a biogas facility but, further adding to the green impacts of the process, some of the CO2 is captured directly from the ambient air, taking the greenhouse gas out of the atmosphere. Another plus - the fuel is sulphur free.

A consortium led by Norsk e-Fuel using the Sunfire process is planning to construct the world's first industrial-size demonstration plant in Norway. The project will utilize renewable electricity, Climeworks' direct air capture technology, and Sunfire's Alkaline electrolyzer (see Figure 1). The plant's first production line is scheduled to start construction in 2023 with production of 12.5 million liters of renewable jet fuel per year anticipated in 2024.

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