Just last month, German car manufacturer Audi invented a carbon-neutral diesel fuel, made from water, carbon dioxide and renewable energy sources, and they say their pilot plant in Dresden will pump out 160 litres of the of the stuff every day in the coming months to power their Audi A8 cars.

Now, they've announced the development of another new type of environmentally friendly, petroleum-free synthetic fuel, which they're calling 'e-benzin'. Manufactured in France by Audi's partner company, Global Bioenergies, the fuel is produced by converting corn-derived glucose - a renewable source of biomass sugar - into isobutane gas. 

Commonly used in refrigeration systems and aerosols, isobutane gas is also one of the staples of the petrochemical industry. About 13 million tonnes of it is extracted annually from oil, and used to produce various types of fuels, plastics and elastomers. In this case, the team at Global Bioenergies refined it into a clear, high-grade, 'unleaded' fuel.

"The next step in the process was to run the material through a conditioning and purification process, allowing it to be collected and stored in liquid form under pressure," Eric Mack reports for Gizmag. "Some of it was then sent to Germany to be converted into isooctane fuel, creating a pure, 100 octane gasoline."

That last point refers to the octane rating of the fuel, which is the standard measure for how much compression a type of engine or aviation fuel can withstand before it ignites. While a low octane rating is better for diesel engines, a high rating is required for gasoline engines, and the higher the rating, the more efficient it is to use.

The team says their Isooctane fuel can be used as an additive to regular unleaded fuel to make it more efficient, or can be used on its own as a fuel. And because their new fuel contains no benzene or sulphur, they say it burns very cleanly. While the next step of the process will be figuring out how to produce the fuel in large quantities, the company also aims to modify the manufacturing process so that no biomass is required - just water, hydrogen, CO2 and sunlight, like how they're producing their new 'e-diesel' fuel.

"We're thinking we're bringing green-ness to a field that desperately needs green-ness," Rick Bockrath, vice president for chemical engineering at Global Bioenergies, told Gizmag. "It's basically how we're moving away from an oil-based economy towards something that has a renewable, sustainable future to it."

With an 'e-gas'- or synthetic methane - being made on an industrial scale already, and projects dedicated to getting 'e-ethanol', Audi 'e-diesel' and Audi 'e-benzin' on the market in the coming years, it's hard not to be impressed by a car company that appears to be so invested in making petroleum-based fuels a thing of the past.