The Thermodynamic and Economic Challenges of Making Fuel From Air

Every few years, a company announces that it is attempting to commercialize the production of fuel from air and water. To be clear, there are no technical barriers against doing this.

Indeed, carbon can be extracted from air, and hydrogen can be produced from water. Together, those building blocks can be reacted to make fuel — or any number of products. I could easily devise a scheme to produce acetaminophen from air and water.

I have addressed these schemes many times over the years. In fact, more than a decade ago, I addressed essentially the same claims from a British company called Air Fuel Synthesis (AFS). (See Investors Beware of Fuel from Thin Air). The company — which now seems to be defunct — made the following claim:

“We haven’t broken the Second Law of Thermodynamics or anything. We take carbon, we combine it with hydrogen, put it in a reactor to make methanol, and then we take the methanol and put that in another reactor to make petrol. The processes of making synthetic petrol from carbon are well known and have been around for many, many years. The Germans were doing it during the Second World War. The South Africans were doing it during the apartheid years. But they were taking their carbon source from coal. We’re taking our carbon source from the atmosphere.”

Since then, we have heard the same story from Audi in 2015 (link), Dimensional Energy in 2018 (which I addressed in a Forbes article here), and now a company called HIF Global (backed by an investment from Porsche AG) is making very similar claims. The story was covered recently in another Forbes article: Inside The Crazy $6 Billion Plan To Turn Wind Into Gasoline.

The problem in each case is the same. Water and carbon dioxide are waste products. When you burn hydrocarbons, like gasoline, these are the waste products. To convert those waste products back into hydrocarbons will always require more energy than you can get from burning the hydrocarbons. That is a fundamental law of thermodynamics.

Thus, the problem becomes one of economics. It’s true that I could devise a scheme to make acetaminophen from air, but that process might cost 10,000 times as much as producing it via conventional methods. The energy requirements of extracting the carbon from carbon dioxide and the hydrogen from water are high. And you will never get back the amount of energy you expended to extract those components.

Further, there are energy inefficiencies in converting hydrogen and carbon into fuel, and further inefficiencies in burning that fuel for power.

But let’s assume for a moment that you have a cheap supply of power, and that the value of the liquid fuel is far greater than the electricity inputs. Thus, one might proceed with such a process, even though it is an energy-losing proposition. It’s theoretically possible that such a process could be economic. As a simple example, you might convert two BTUs of coal into one BTU of liquid fuel if the liquid fuel was valued at three times the value of the coal. It’s inefficient but could be economical.

This is a niche that HIF Global hopes to exploit. They are using cheap wind power in Patagonia as a fundamental energy input into this process. Cheap power is the only possibility of getting a process like this to work economically, but cheap power often occurs in remote locations. That, in turn, creates logistical problems in getting any liquid fuel produced to market in an economical manner.

It would probably make more sense to put that cheap power into power lines, and then use that to power electric vehicles (or to back fossil power out of the grid). Stopping at electricity production is more energy efficient than converting to fuel, and electric vehicles are more energy efficient than combustion engines.

In short, there’s no free lunch. Even though the concept has been around for a long time, nobody has managed to commercialize the production of fuel from thin air. Thermodynamics ensures that this will always be an extremely challenging prospect.