How to make fuel from thin airBob Jennings may be a modern-day alchemist, turning air into liquid gold. The Technical Director of Air Fuel Synthesis explains his company's breakthrough.
The original intention was to produce aviation fuel by reacting carbon dioxide extracted from the air with hydrogen extracted from water (using renewable electricity) to make hydrocarbons. The two fuels I see us making initially are methanol and gasoline. Methanol has lots of applications but our main thrust is to convert that methanol into gasoline.
In New Zealand, in the 1990s, Mobil Corp. made synthetic gasoline from methanol. We have our own version of that process. The difference is that they used natural gas while we are using wind energy, recovered CO2, and electrolytic hydrogen.
How do you capture CO2 from the air?
We use a “scrubbing column”—a large tower containing alkali. CO2 and water produce a weak acid which reacts with the alkali creating bicarbonate which you then process from which to recover the carbon dioxide. This is done thermally by heating it up to 100 degrees plus, under slight pressure.
How much air do you need to create a liter of fuel?
An awful lot; the concentration of CO2 in air is only about 0.035 percent so to get sufficient kilograms of CO2 you have to process about 4000 meters cubed of air.
That is why we have mostly been using commercial CO2 from bottles, mainly by-products of bioethanol, ammonia or hydrogen plants. While we can capture CO2 from air, it is difficult and more concentrated sources of CO2 are more economically viable at the moment.
How does your technology make fuel?
We mix and compress the carbon dioxide and hydrogen and pass the gas mix over a commercial catalyst which partially converts it into methanol. The CO2/H2 mix not converted is recycled back into the reactor. The product we get is about half methanol and half water. We separate that so we have a purified methanol stream for our gasoline reactor.
In the gasoline reactor we feed the methanol through a heat exchanger and then a conversion reactor to make hydrocarbons and water. We get approximately 10 parts gasoline for every 30 parts methanol.
How much CO2 do you need to make a liter of fuel?
We need 3.9kg of CO2 to make one kilogram, or about 3.1kg to make one liter of gasoline. A typical ammonia plant would make well over 1000 tons of CO2 per day. So a large gasoline reactor would probably use all the CO2 from a very large ammonia plant.
We need about 30 kilowatts of power to make one kilogram of gasoline. The main energy cost is the cost of making the hydrogen through electrolysis of water. Most hydrogen is manufactured by steam reforming fossil fuels but our objective is to use sustainable energy, mainly wind and perhaps solar.
To make a ton of gasoline we would need about four and a half tons of water. However, all the water used to make the hydrogen is regenerated during methanol and gasoline synthesis, and some could be recycled.
Would you need to locate production plants near large water sources?
On a small scale, probably not. But if we are talking about refinery scale, It would be useful to have access to large amounts of water. Equally important is being close to large amounts of CO2.
What scale are you working at now?
We have a one-liter reactor for methanol, capable of making about one kilogram an hour. The gasoline reactor should give us about half that amount although in practice it is a little less at the moment.
We are making methanol and gasoline every day and are trying to advance them for evaluation. We consider the technology as proven, and so now we are looking at building a ton-a-day gasoline unit. I would like to see us have something to show on the ground in two years, although it depends entirely on funding. We need external investors and are applying for UK government grants.
When will you have a vehicle running on your fuel?
We are hoping to do something with a small vehicle. Our goal for this year is to have some motorized transport running entirely on our fuel.
It depends on scale. Up to a ton day we are definitely looking at a niche market but there is no technical reason why this couldn’t be done at a very large scale, hundreds or even thousands of tons a day. Our long-term vision would be refinery scale which would be several hundreds of tons a day.
So who will be your first customers?
A lot of gasoline users have a requirement for sustainable fuel elements in their fuel. Motor racing is one example. Conventionally they use bio-ethanol. The advantage of using our gasoline is it has a higher energy density and it doesn’t take up land that could be used for food.
Some of the fleet markets are being required to reduce their carbon emissions. We argue that our fuel is CO2 neutral and on that basis that could be blended directly into existing fuels to help people meet targets.
Have you been certified as CO2 neutral by independent bodies?
That is what we are working on. If we take it from air obviously it is. If we take it from a brewery or distillery, it is. We would argue if we take it from a power station it is because firstly, we are preventing the emission of that CO2, and second, we are getting twice the value of the CO2 that is emitted because the same carbon is being used twice.
Who have you demonstrated your technology to?
We have demonstrated to carmakers, and just written a joint paper with Lotus for example on blended fuels. One of our early targets is a Lotus car using fuel in a blend, that’s what we hope to see happening. We are in discussions with a petroleum blending company which has shown great interest because we make a high-octane hydrocarbon mixture with a rating of approximately 94. That could be used with very little refining.
What is your anticipated cost per liter of fuel?
I can’t give an exact number because it is very dependent on scale, the cost of power, whether you get carbon credits for it, what the feed-in tariffs are. It is a very complex question. I will say at the ton-a-day scale we would be competitive with other applications in niche markets such as racing fuels. We are offering a payback in a small number of years.