How Carbon-neutral E-fuels Work

Like many people and corporations, Audi seems to be working hard to reduce its carbon footprint. If you're not familiar with that term, or its relative, carbon offsets, then you might want to check out How Carbon Footprints Work and How Carbon Offsets Work. In the meantime, here's a quick primer: A carbon footprint measures all carbon dioxide (CO2) emissions produced by a single person or business. Carbon dioxide is the primary greenhouse gas produced by human activities, so that's why it receives most of the attention. But an accurate carbon footprint measurement also accounts for other gases, such as methane and chlorofluorocarbons. Scientists express carbon footprints in tons of CO2 or CO2 equivalents per year.

If you reduce the CO2 emissions related to a certain activity, then you decrease that activity's footprint. If you cut emissions so that they equal the footprint, then you achieve what's known as carbon neutrality. Companies tackle this problem in many different ways. Some build wind farms to replace coal-fired power plants. Others engage in carbon sequestration activities, such as planting trees to trap carbon dioxide in forests and soils. And still others participate indirectly by funding projects that reduce greenhouse gas emissions. All of these methods qualify as carbon offsetting.

Transportation, which often relies on burning fossil fuels to move people and goods, poses a significant challenge in the fight to reduce carbon output. It takes a lot of electricity from a CO2-spewing power plant to build a car -- and even more to extract, refine and deliver the petroleum products to fill its gas tank. And then, once the car gets on the road, its internal combustion engine produces a steady supply of greenhouse gases, which collect in the atmosphere and become part of a great, planet-warming blanket. Electric and hydrogen-powered vehicles could eliminate some of these issues, but they may not be viable solutions for years.

Despite these challenges, Audi has dedicated itself to "balanced mobility," which the company defines as "holistic, CO2-neutral mobility over short, intermediate and long distances" [source: Audi USA]. E-gas, a fuel that can power internal combustion engines, plays an important role in this effort. How can Audi hope to achieve carbon neutrality with an old-school technology? It will actually use carbon dioxide as a raw ingredient to make its engine-friendly fuel. A refuse biogas plant will provide the CO2, and a purpose-built factory in Werlte, Germany, will carry out the necessary chemical reactions. Beginning in 2013, the factory in Werlte will consume 2,800 metric tons of CO2 and will generate 1,000 metric tons of e-gas a year [source: Audi USA]. This, combined with other green practices we'll explore a bit later, will enable Audi to achieve carbon neutrality across its entire value chain.

Chemists and consumers know e-gas by another name: methane, or natural gas, which is already used extensively to heat homes and to power natural gas vehicles. On the next page, we'll take a closer look at this synthetic gas and the chemistry required to produce it.