By - Jim Vess

Synthetic Fuel from Wind and Solar Power? Audi Thinks So.

Audi Prologue

Tesla claims the future of car travel is all about electric motors and batteries. Toyota believes that electric cars aren’t practical and is developing hydrogen-powered vehicles. Now Audi, along with development partner Sunrise, says it may have the best alternative yet – synthetic fuel made from water and carbon dioxide (CO2) using wind- and solar-generated electricity to power the production process.

Audi has set up an experimental production facility in Dresden, Germany, which is producing a synthetic form of diesel using just water and CO2. The synthetic fuel can be used in existing diesel engines without any modifications being required, either as a mix with gasoline or as a complete fuel solution on its own.

The production process does require resources, but Audi claims it is a green energy source based on how it is produced and the use of renewable energy sources for initial heating. In the process, water is heated to form steam which is then broken down into hydrogen and oxygen using high-temperature electrolysis, which requires a temperature of 800 degrees Celsius. Audi and Sunrise use heat recovery to ensure an efficient system.

The CO2 for this process comes from a biogas facility and through direct air capture. The CO2 reacts with the hydrogen in a synthesis reactor under pressure – approximately 370 psi – at about 220 degrees Celsius to produce a liquid called blue crude. It is then refined to become e-diesel, which is free of both sulfur and aromatic hydrocarbons.

According to Audi, the efficiency of the overall process – from renewable power to liquid hydrocarbon – is very high at around 70 percent.

Attempts to create synthetic fuels from sources of carbon and hydrogen have existed for over a century. In 1913, Friedrich Bergius developed methods of hydrogenating carbon by exposing powdered coal to very hot steam at high pressure in the presence of a catalyst.

Chemists Franz Fischer and Hans Tropsch, around 1925, went at the process differently, by using carbon monoxide (CO) instead of coal, exposing the CO to hydrogen in high-pressure reactors at extremely high temperatures.

Before and during World War II, Hitler ordered large-scale construction of Fischer-Tropsch reactors to help make up for Germany’s lack of oil. In the end, limited availability of steel and Allied bombings kept the number of Germany’s fuel synthesis reactors small.

After World War II, the availability of plentiful Texas natural gas, delivered nationwide by pipeline resulted in a loss of interest in synthetic fuels.

The OPEC oil embargo in the early 1970’s drove up oil prices restarted worldwide interest in synthetic fuel processes, but oil’s subsequent price seesaw has made investors cautious.

While there have been several attempts to produce affordable synthetic fuels, Audi’s and Sunrise’s process may be the one that succeeds. Using low cost electricity generated from wind and solar facilities, getting CO2 from a biogas facility, and using heat recovery to increase efficiency, theirs could be the first truly “green” process to produce a synthetic fuel.

This author believes that all forms alternate power – electric, fuel cells, and synthetic fuel have a place in the transportation mix. But a car that runs on water? How cool is that?

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