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“Energiewende” in a tank; Audi e-fuels targeting carbon-neutral driving with synthetic fuels from renewables, H2O and CO2; Swiss policy test case

Like other major automakers, Audi (and its parent Volkswagen Group) is working on meeting its medium-term regulatory requirements (e.g., in the 2020 timeframe) by reducing the average fuel consumption of its new vehicles using a combination of three primary measures: optimizing its combustion engines for greater efficiency; developing alternative drive concepts, such as hybrid, plug-in hybrid and gas-powered vehicles; and reducing total vehicle weight through lightweight construction with an intelligent multimaterial mix.

Unlike the others, however, Audi over the past few years has embarked on a comprehensive approach to developing a range of new CO₂-neutral fuels as part of its overall strategy for sustainable, carbon-neutral mobility: Audi e-fuels. Audi’s basic goal is to combine renewable energy (e.g. solar and wind), water and CO2 to produce liquid or gaseous fuels with a very low carbon intensity. Audi e-fuels are intended to use no fossil or biomass sources; do not compete with food production; and are 100% compatible with existing infrastructure.

The principle of Audi e-fuels, said Reiner Mangold, Audi Head of Sustainable Product Development, to an audience at a technology briefing on the use of power-to-gas technology in mobility held at Empa (Swiss Federal Laboratories for Materials Science and Technology) in February, is to use CO2 as a raw material in fuel production and incorporate it into a closed carbon cycle.


“Energiewende”, the term applied to Germany’s policy of transitioning to an energy portfolio dominated by renewable energy (as well as a shift to more distributed generation), thus also applies to the vehicle fuel tank for Audi’s e-fuels, Mangold suggests.

The company currently has a number of projects underway producing or developing—with its different technology partners—e-gas (methane) (earlier post); e-ethanol (earlier post); two versions of e-diesel from different pathways (earlier post, earlier post); and e-benzin (gasoline) (earlier post).

Underneath the e-fuels banner, Audi also includes renewable electricity for recharging its e-tron vehicles (“e-power”) and, should the market so require it, “green” hydrogen (e-hydrogen, derived in the e-gas process).

Audi sees the potential for the use of CO2-neutral fuels to reduce fleet CO2 emissions. In addition to the technology, however, regulatory progress would need to be made to recognize the gains. Click to enlarge.

Audi has an increasingly strong electric drive initiative in place, including the top-end limited production battery electric R8 e-tron (earlier post); the Q7 e-tron plug-in hybrid (diesel) (earlier post); the Q7 e-tron 2.0 TFSI and A6 L e-tron plug-in hybrid for the China market (earlier post); and the A3 Sportback e-tron plug-in hybrid (earlier post).

In March, during his speech at Audi’s Annual Press Conference in Ingolstadt, Prof. Dr.-Ing. Ulrich Hackenberg, Member of the Board of Management at Audi AG for Technical Development stated that Audi will have a plug-in hybrid in every model series in the coming years as part of its efforts in efficiency and sustainability. (Earlier post.)

Audi sees the development of its low CO2 e-fuels as a means of supplementing e-mobility; as the fuel for combustion engines in a plug-in hybrid powertrain, for example, or simply as a fuel to lower the CO2 footprint of existing vehicles.

We have to find a solution for mobility in total, including trucks and planes. We thought that when we find a way to capture CO2, and we can combine hydrogen with the CO2 and take off the O2, then maybe we would have a solution.

—Reiner Mangold

To be clear, said Sandra Novak, Audi Regulatory Engineer who now works on the e-fuels projects out of the Volkswagen Group of America office in Auburn Hills, MI, Audi itself is not in the partner companies’ labs; Audi is, however, “pushing the companies in the right direction”—i.e, to the realization of the renewable energy + water + CO2 formula.

From its beginning with a single pilot project (Audi e-gas), the Audi e-fuels portfolio has now advanced to the point where it is referenced in the most recent corporate responsibility report, assigned a target (market introduction in 2019), and a percent completed mark (10%).

From Audi’s latest Corporate Responsibility Report. Click to enlarge.

Now we imagine the maximum scenario: e-tron plug-in hybrid drive under the hood and e-fuel in the tank. We will drive electrically in urban areas and with synthetic gasoline and diesel outside cities. In this way, we will achieve CO2-neutral mobility without limiting our cars’ range.

—Rupert Stadler, Audi CEO, at the International Vienna Motor Symposium in 2014

Audi e-gas. The e-gas project, announced in May 2011, was Audi’s first foray into e-fuels. E-gas is synthetic methane produced via the methanation of hydrogen produced by electrolysis using renewable electricity. (Earlier post.) In June 2013, Audi commissioned a power-to-gas facility in the north German town of Werlte, thus becoming the first automobile manufacturer to develop a chain of sustainable energy sources. The plant has been in normal operation since late 2014.

The Audi e-gas plant can convert 6MW of input power. The e-gas is virtually identical to fossil natural gas and is distributed via an existing infrastructure—the German natural gas network—to the CNG filling stations beginning in Germany in fall 2013.


The e-gas plant only operates when there is too much electricity from renewable sources in the grid. According to current estimates, the plant will be in operation roughly half the year and will produce around 1,000 metric tons of Audi e-gas. This amount binds some 2,800 metric tons of CO2, or roughly the amount absorbed each year by a forest of 220,000 beech trees, Audi calculates. Around 1,500 Audi A3 Sportback g-tron cars can be driven 15,000 carbon-neutral kilometers (9,300 miles) each year on the e-gas from Werlte, since the CO2 emitted from the exhaust system had been bound previously during the production of the e-gas.

Customers can order a supply of Audi e-gas when purchasing their g-tron. To fill up with e-gas, customers show their Audi e-gas refueling card when paying. The card is used to centrally record the amount of gas consumed. This exact amount of e-gas is then fed into the distribution network at Werlte.

Partnership with Joule: e-ethanol and e-diesel. In 2012, Audi entered into a collaboration with Joule for the direct production of e-ethanol and e-diesel hydrocarbons (n-alkanes) from photosynthetic cyanobacteria. (Earlier post.)

Audi operates a research facility in Hobbs, New Mexico for the production of e-ethanol and e-diesel in partnership with Joule. At this facility, the engineered microorganisms use water (brackish, salt or wastewater), sunlight and carbon dioxide to produce the fuels.

In 2014, Audi testing of synthetic ethanol (Audi e-ethanol = Joule Sunflow-E) and synthetic diesel (Audi e-diesel = Joule Sunflow-D) in a pressure chamber and optical research engine showed that the Audi e-fuels often perform better than their conventional counterparts. (Earlier post.) In May 2015, testing initiated by Audi confirmed that Joule’s e-ethanol meets: ASTM International D4806 – Denatured fuel ethanol for blending with gasolines for use as automotive spark-ignition engine fuel; and German Institute for Standardization (DIN) EN 15376 – Ethanol as a blending component for petrol.

Global Bioenergies: e-gasoline. In early 2014, Audi took the next step in the development of renewable fuels and entered into a strategic partnership with Global Bioenergies for the development of a process to produce e-gasoline (e-benzin)—specifically a renewable isooctane derived from Global Bioenergies’ renewable isobutene, produced by engineered microorganisms fermenting sugars. (Earlier post.)

Isobutene—a four-carbon branched alkene and one of four isomers of butylene (C4H8)—is a molecule with multiple applications, one of which allows its transformation into isooctane. The process to convert isobutene to isooctane is well-established. Isobutene dimerization (putting two isobutene molecules together) and subsequent hydrogenation produces isooctane. (The trimerization of isobutene produces tri-isobutenes, which can be used as a premium solvent and as an additive for jet fuel.)

Pure isooctane (2,2,4 trimethylpentane) has both a high research octane number (RON) and a high motor octane number (MON): 100 RON and 100 MON. A low Reid vapor pressure of 1.8 psi make it also attractive for bending into reformulated gasoline. As a 100% drop-in fuel, isooctane can be used in any blending ratio with all standard fuels for gasoline motors.


In May, Global Bioenergies presented the first batch of e-benzin to Audi by Global Bioenergies during a press conference.

However, Global Bioenergies’s current production pathway—fermenting sugars derived from starch or biomass—doesn’t fully mesh with Audi’s basic e-fuels criteria: water, CO2 and renewable energy. Thus, the two companies are now working on a technology allowing the production of renewable isooctane not derived from biomass sources. (Earlier post.)

Blue crude and e-diesel. Audi’s most recent partnership in the e-fuels arena surfaced in November 2014, when the company opened a pilot plant with project partners Climeworks and sunfire in Dresden for the production of synthetic diesel from water, CO2 and green electricity. (Earlier post.) The pilot plant is also demonstrating that industrialization of liquid Audi e‑fuels is also possible. Vehicles filled up on the first high-grade e-diesel fuel in mid‑April. (Earlier post.)

The project, which is funded in part by the German Federal Ministry for Education and Research and was preceded by a two-year research and preparation phase, combines two innovative technologies: direct capture of CO2 from ambient air and a power‑to‑liquid process for the production of synthetic fuel. Audi is the exclusive partner in the automotive industry.

Other partners in the project consortium include Lufthansa; Fraunhofer ICT; Universität Stuttgart; Forschungszentrum Jülich; GEWI AG; CVT Chemical Engineering; and HGM.

The sunfire plant, which operates according to the “power-to-liquid” (PtL) principle, requires carbon dioxide, water and electricity as raw materials. The carbon dioxide is extracted directly from the ambient air using direct air capture (DAC)—a technology developed by Swiss partner Climeworks.

The Climeworks CO2 capture technology is based on a cyclic adsorption / desorption process on a novel filter material (“sorbent”). During adsorption, atmospheric CO2 is chemically bound to the sorbent’s surface. Once the sorbent is saturated, the CO2 is driven off the sorbent by heating it to 95 °C, thereby delivering high-purity gaseous CO2. The CO2-free sorbent can be re-used for many adsorption/desorption cycles. Around 90% of the energy demand can be supplied by low-temperature heat; the remaining energy is required in the form of electricity for pumping and control purposes.

In a separate process, a solid oxide electrolysis (SOEC) unit powered with green electricity splits water into hydrogen and oxygen. (sunfire acquired staxera, a developer and manufacturer of SOFC high-temperature fuel cells sited in Dresden in 2011.) The hydrogen is then reacted with the CO2 in two chemical processes conducted at 220 ˚C and a pressure of 25 bar to produce a hydrocarbon liquid called Blue Crude. The process is up to 70% efficient.

Nearly 80% of the Blue Crude can be converted into synthetic diesel using existing refinery technologies. This fuel—Audi e‑diesel—is free of sulfur and aromatics, and features a high cetane number. Its chemical properties allow it to be blended in any ratio with fossil diesel—i.e., it can be used as a drop-in fuel.

We are trying to build awareness that you can make a climate impact with existing cars. We don’t have to wait for everyone to buy an EV or hydrogen fuel cell vehicle.

—Reiner Mangold

The policy side; test case in Switzerland. Audi’s e-fuels portfolio, especially on the liquid fuel side, is still in development, with the medium-term goal of industrial-scale commercialization. In the longer term, e-fuels enabled CO2-neutral driving could help close up any gaps Audi might have between its fleet performance and regulatory CO2 targets—but only assuming the legal recognition for such fuel-enabled low carbon driving can be worked out.

Switzerland’s Two-Chamber Parliament
The National Council is similar to the US House of Representatives. The 200 members are elected every four years according to a proportional election system.
The Council of States, like the US Senate, represents the Swiss cantons. Full cantons send two members, half cantons one, giving a total of 46 members.
Both chambers discuss new laws separately. A motion will need to be approved by both councils.

A test case for that is emerging in Switzerland, where the government is considering a motion to include synthetic, CO2-neutral fuels within the CO2 fleet emission regulation.

(As noted above, Climeworks, which provides the solution for efficiently capturing CO2 out of ambient air for use in the Blue Crude process, is a Swiss company.)

In December 2014, Thomas Böhni, member of the Swiss Parliament from the Canton of Thurgau, submitted a motion for consideration by the National Council (Nationalrat) that would:

  1. Create the legal basis for importers and manufacturers of vehicles that run on CO2-neutral synthetic fuels made in Switzerland to receive credit for the corresponding reduction in CO2 emissions under fleet emission rules; and

  2. Commission the development of an administrative procedure for calculating these credits based on individual vehicles.

CO2 neutral synthetic fuels enable virtually climate-neutral mobility with enhanced added value in the domestic market that can make use of the existing infrastructures and passenger cars. Allowing the credit procedure would materially support achievement of the mobility climate goals—quickly, comparatively easily, and without having to subsidize a new renewable source of energy.

… A regulation governing the use of biogas is already in place as an industry solution for vehicles powered by natural gas. Further continuous expansion of the share of renewable energy used in mobility is an effective means of achieving virtually CO2-neutral mobility in the long run.

CO2-neutral synthetic fuels are manufactured using Power-to-Gas/Liquid technology from renewable energies and CO2, which is separated from ambient air, for example. A closed carbon cycle is produced during the combustion process. Synthetic fuels are manufactured virtually entirely from renewable energies, with only minimal net CO2 emissions being produced as a result.

The key technology for splitting CO2 from ambient air at reasonable cost was developed in Switzerland. It has not yet been possible to include it in statutory and regulatory measures. The automobile industry already invests in the production of CO2-neutral synthetic fuels. Further major investments aimed at rapid expansion are planned and would be helped enormously by inclusion of the credit procedure under fleet emission rules.


richard schumacher

Excellent. Now when the hell are we going to see retail products? I would happily pay $6 per gallon for carbon-neutral gasoline for my Prius.

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