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Delivery of renewable isooctane to Audi tips interesting potential non-biomass pathway for biogasoline; “e-benzin” as solar fuel

Last week, Audi and its partner Global Bioenergies announced that the first batch of renewable isooctane—which Audi calls “e-benzin”—using Global Bioenergies’ fermentative isobutene pathway (sugar→isobutene→isooctane) had been produced and presented to Audi by Global Bioenergies. (Earlier post.)

Global Bioenergies, founded in 2008, has developed a synthetic isobutene pathway that, when implanted in a micro-organism, enables the organism to convert sugars (e.g., from starch and biomass) via fermentation into gaseous isobutene via a several-stage enzymatic process. However, following the delivery of the first renewable isooctane, Reiner Mangold, Audi’s head of sustainable product development, said that Audi was “now looking forward to working together with Global Bioenergies on a technology allowing the production of renewable isooctane not derived from biomass sources”—i.e., using just water, H2, CO2 and sunlight.

Thomas Buhl, Head of Business Development for Global Bioenergies, confirmed that his company’s goal is to make its technology compatible with first-generation biomass, second-generation biomass and “non-biomass” feedstock.

Although there has been no public announcement or discussion of what such an Audi/Global Bioenergies development effort might entail, in 2011, Global Bioenergies began a feasibility study to examine whether its artificial isobutene pathway could be functionally transferred into LanzaTech’s carbon monoxide-using organism (earlier post).

LanzaTech, founded in 2005, has developed a novel gas-liquid fermentation process that produces fuels and chemicals from gas resources and is the first company to successfully demonstrate production of fuel-grade ethanol from steel mill gases. This proprietary novel gas fermentation technology converts the carbon monoxide-containing waste gases emitted by blast furnace, coke oven and BOF (basic oxygen furnace) operations into low-cost ethanol and high-value chemicals. (Earlier post.)

The addition of Global Bioenergies’ synthetic isobutene pathways into the LanzaTech organisms would presumably offer another end product for the LanzaTech process.

However, in 2014, LanzaTech signed a research and development agreement with its partner INVISTA to collaborate on the development of gas-fermentation process technology for the production of industrial chemicals from CO2 and H2 using proprietary INVISTA host organisms and metabolic pathways. If successful, the first commercialization of this technology is expected as early as 2018. (Earlier post.)

Again emphasizing that there has been no announcement of development direction, the potential building blocks for a solar fuels isooctane process are emerging. Neither Global Bioenergies or LanzaTech would comment, citing confidentiality agreements.

Isobutene and isooctane. Isobutene (C4H8, an isomer of butylene) is one of the major building blocks of the petrochemicals industry, with a current market worth of $25 billion that may eventually address an additional market worth $400 billion. 15 million tonnes are produced every year and are turned into plastics, rubbers and fuels.

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.)

The basic process for the oligomerization of light olefins (isobutene and isobutane) in FCC units at refineries has received attention for a number of years in terms of catalyst design and process tuning. Selectivity problems and catalyst deactivation can hinder the critical isobutene dimerization reaction. The hydrogenation step can use either noble metal or non-noble metal catalysts. Although non-noble metal catalysts are less prone to deactivation and fouling, they require high hydrogen partial pressures, resulting in higher costs.

Further, there is interest in developing alternatives to the conventional process for isooctane production via dimerization of isobutene and hydrogenation. For example, a team from the University of Waterloo earlier this year published a paper proposing a catalytic distillation process for the more energy efficient production of isooctane from isobutene (Goortani et al.).

In addition to the isobutene to isooctane pathway, noted Buhl, there is another option that might be less costly:

Another approach would be to take just one bio-isobutene, and one isobutane [C4H10, an isomer of butane], in this case no H2 needed. Isobutane is 30 to 40% cheaper than regular gasoline but cannot be used (significantly) in fuel because of its high volatility. So here our isobutene would allow us to integrate this very cheap fossil component into the fuel.

—Thomas Buhl

Audi e-fuels. Audi is active in the development of CO2-neutral, synthetic fuels, which it calls, collectively, e-fuels. In addition to its work with Global Bioenergies, Audi has projects underway with Joule in the US for the development and testing of synthetic ethanol and synthetic diesel (earlier post); has an e-gas project underway in Werlte, Germany (earlier post); and has a new partnership with Climeworks and sunfire on producing synthetic diesel from water, air-captured CO2 and green electricity (earlier post).


  • Behnam M. Goortani, Aashish Gaurav, Alisha Deshpande, Flora T. T. Ng, and Garry L. Rempel (2015) “Production of Isooctane from Isobutene: Energy Integration and Carbon Dioxide Abatement via Catalytic Distillation” Industrial & Engineering Chemistry Research 54 (14), 3570-3581 doi: 10.1021/ie5032056


Kevin Cudby

I think this is a fair assessment. Audi management are undoubtedly aware that solar fuel exploits a resource that is more than adequate to satisfy long-term demand for liquid fuels
The Sunfire experiment exemplifies a pathway that "should" work. Each step in their process is based on known technology. What we don't have, yet, is a commercial-scale demonstration of direct capture of carbon dioxide from the atmosphere. Carbon Engineering and the Sunfire partner (Climeworks) are working toward this goal. The big question will be: "What will it cost?" Based on Carbon Engineering's cost estimate, I calculated that solar gasoline should be at least as affordable in the late 21st century as fossil gasoline is today. Sunfire's cost estimate is considerably more optimistic than mine.
If, as you suggest, Audi is pursuing an alternative route, in parallel with Sunfire, I think they are doing the right thing. If it's more economic than a "Sunfire-like" process, then it would be possible to accelerate the phase out of fossil fuels without crimping the world economy.
Another possibility is that Audi wants iso-octane as a blendstock. Sunfire's gasoline fraction will have an octane rating of 80 or so. Boosting the octane rating adds cost. (Not a lot, but every little bit adds up). A low cost source of iso-octane might help reduce the cost of finished solar gasoline by reducing the need for isomerisation.


Sequestered CO2 can be used for this and other uses.


It strikes me that the best way to capture CO2 from the air is from the air immediately outside a stack in a power station.
i.e. build the plants to take the CO2 directly from the power stations.
A ton of CO2 is the same whether it comes from a power station or a clear blue sky, but much more concentrated at the power station. (Also much hotter ? - not sure on that one).

Also, I see no reason to use waste biomass to make fuel (wood offcuts, straw, low grade wood etc.)


I see no reason to use waste biomass to make fuel

I do. Ask yourself where they will put said waste if they don't use it. A lot of the biomass you listed is currently disposed of by burning which not only puts their carbon back into the air as CO2 but also produces particulate pollution. Or it is left to rot which adds methane to the problem.

Also landfills are filling up fast and its getting harder to find new sites for them. If we can divert the bio component from MSW to biofuel that would cut costs of disposal.


Cellulose ethanol, gasify the remains for synfuels.


@SJC - I meant to say "I see no reason NOT to use waste biomass..."
However, you are right in your analysis, there are lots of reasons to get rid of waste biomass as profitably as possible.
You underlined the point I meant to make!


Sure, I can see solar hydrogen with sequestered carbon benefiting from power plant waste heat to make fuels. There are many ways we can get rid of imported oil.

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