Research facility in Dresden produces first batch of Audi e-diesel; sunfire’s power-to-liquid technology
A pilot plant in Dresden has started production of the synthetic fuel Audi e-diesel using water, CO2 and green power—i.e., power-to-liquid (PtL). After a commissioning phase of just four months, the research facility in Dresden started producing its first batches of high‑quality diesel fuel a few days ago. (Earlier post.)
The energy technology company sunfire is Audi’s project partner and the plant operator. The CO2 used is currently supplied by a biogas facility. In addition, initially a portion of the CO2 needed is extracted from the ambient air by means of direct air capturing, a technology of Audi’s Zurich‑based partner Climeworks.
To demonstrate its suitability for everyday use, Federal Minister of Education and Research Prof. Dr. Johanna Wanka put the first five liters into her official car, an Audi A8 3.0 TDI quattro.
In developing Audi e-diesel we are promoting another fuel based on CO2 that will allow long‑distance mobility with virtually no impact on the climate. Using CO2 as a raw material represents an opportunity not just for the automotive industry in Germany, but also to transfer the principle to other sectors and countries.—Reiner Mangold, Head of Sustainable Product Development at Audi
Production of Audi e‑diesel involves a series of steps:
Water heated to form steam is broken down into hydrogen and oxygen by means of high-temperature electrolysis. This process, involving a temperature in excess of 800 degrees Celsius, is more efficient than conventional techniques because of heat recovery. High-temperature electrolysis is that it can be used dynamically to stabilize the grid when production of green power peaks.
The hydrogen reacts with the CO2 in synthesis reactors under pressure and at high temperature. The reaction product, known as blue crude, is a liquid made from long‑chain hydrocarbon compounds. The efficiency of the overall process—from renewable power to liquid hydrocarbon—is around 70%.
Similarly to a fossil crude oil, blue crude can be refined to yield the end product Audi e‑diesel. This synthetic fuel is free from sulfur and aromatic hydrocarbons, and its high cetane number means it is readily ignitable. As lab tests conducted at Audi have shown, it is suitable for admixing with fossil diesel or, prospectively, for use as a fuel in its own right.
|Two cartoons of the basic sunfire concept and process. PtL = Power-to-Liquids. Source: sunfire. Click to enlarge.|
The Federal Ministry of Education and Research is supporting the sunfire project, which started in May 2012. Construction work on the facility in Dresden‑Reick kicked off in July 2013 and the plant was commissioned on 14 November 2014. The plant is set to produce more than 3,000 liters (792.5 gallons US) of Audi e‑diesel over the coming months. Audi is sunfire’s exclusive partner in the automotive sector.
In addition to the partnership with sunfire, Audi has been active in the development of CO2‑neutral fuels—Audi e‑fuels—since 2009. The Audi e‑gas plant in Werlte, Lower Saxony, already produces Audi e‑gas (synthetic methane) in a comparable manner; drivers of the Audi A3 Sportback g‑tron can fill up on it using a special fuel card. Audi is also conducting joint research into the synthetic manufacture of Audi e‑gasoline with Global Bioenergies, of France. In a further project, Audi has joined forces with the US company Joule, which uses microorganisms to produce the synthetic fuels Audi e‑diesel and Audi e‑ethanol.