Sorry Everyone, Making Fuel Out of Seawater Isn't Gonna Save Us

Navy experts trying to power a tiny aircraft with a liquid hydrocarbon fuel (Photo: US Naval Research Laboratory)

Last week, some people at the US Naval Research Laboratory’s Materials Science and Technology Division were able to successfully fly an aircraft fuelled by nothing but seawater. Of course, the seawater was converted into a liquid hydrocarbon "jet fuel" first, and the aircraft was a scale replica of a WWII-era fighter that even a Ken doll would find pretty cramped, but it was a pretty successful demonstration of a technology that researchers have been working on for decades now – turning the CO2 and Hydrogen stored in the world’s oceans into useful fuel.

News of this achievement flew around the internet at a fair old pace, with journalists racing to see who could misunderstand the Navy’s press release the fastest. At one extreme, the International Business Times painted the US Navy as a sort of heavily armed ocean-going Womble brigade, sucking up the world’s CO2 emissions and turning them into shiny new products. But even as they waved “Goodbye Oil”, conservative-minded folk like the American Spectator’s William Tucker rattled angrily about "perpetual motion machines" and the collective shoddiness of the liberal press.

So which is it? Let’s look at the technology:

The basic premise is this: Jet fuel is made out of hydrocarbons, which are organic molecules that contain hydrogen atoms and carbon atoms. The biggest natural stores of hydrocarbons are the planet’s crude oil reserves, but they’re increasingly hard to reach, and have a habit of popping up in really inconvenient places, like Iraq. There is another massive store of hydrogen and carbon, though – the world’s oceans. Water molecules contain Hydrogen – the "H" in H20 – and vast quantities of carbon dioxide are dissolved in seawater, (an amount that’s growing thanks to industrial CO2 emissions, and making the world’s oceans increasingly acidic).

What if, instead of having to drill for oil, we could extract the carbon and hydrogen available in the oceans, and turn them into hydrocarbons? We’d have to do more work converting H20 and CO2 into something useful than we do with crude oil, but on the flip side we’d be using a plentiful resource that’s available to pretty much anyone but the Swiss, and they don't need an army anyway. If you’re a large naval warship, you’re literally swimming in the stuff.

The snag is how to actually take that raw material and process it. The US Navy experiments use electricity to split hydrogen from seawater as a gas, use an electrochemical system to recover CO2 gas from the same water and react the two gases together to create hydrocarbon liquid. According to their press release, they can get about 97 percent of the CO2 out of the water, and convert about 60 percent of the extracted gases into hydrocarbons that can then be processed into jet fuel.

If you’re paying attention you might have noticed some problems with this plan. The most obvious is that to do all of this you need a ton of energy in the first place, not just to run the process but to pump up all this seawater initially. If your ship is generating electricity from fuel, then you’re going to end up burning more than you actually create with this process. In order for this to make sense, then, you need something more hardcore… something like the reactor on a nuclear-powered aircraft carrier.

In fact, if you actually read some of the reports out of this project, nuclear power is exactly where they’re going with it, but that point was completely missed by the International Business Times and other reporters, as the American Spectator rightly point out. That may not be such a big issue, though. Nuclear power is one of the cleanest and most practical alternative energy sources around at the moment, and even if the fuel costs more to produce, you’re saving on the cost of getting that fuel where it’s needed and ensuring the ability of your fleet to operate even in the event that their supply chain is disrupted. Strategically, it makes a lot of sense.

A bigger issue is the waste and inefficiency of the process. It’s true that the concentration of CO2 in seawater is a lot higher than it is in the air, but that’s still a really tiny amount. To get a significant amount of gas, you’re going to have to process a pretty huge volume of seawater, and then when you compress that gas into a liquid, it’s going to shrink considerably. A 2010 report estimates that in order to produce 100,000 gallons of jet fuel in a day – assuming 100 percent efficiency in the process – “the minimum amount of seawater that must be processed in 8,900,000 cubic metres. This is equivalent to a cube of seawater that is about 200 metres on each side.”

In real life, you’d expect it to be probably twice that, which isn’t as much as it could be, but is still a hell of a lot.

And then there are the emissions. I mentioned earlier that only about 60 percent of the gas produced is successfully converted into useful fuel. About 25 percent comes out of the process as methane, one of the worst greenhouse gases around. Then, of course, there’s the problem that you’re extracting CO2 out of the ocean, putting it in aircraft and pumping it straight back into the atmosphere.

For all the talk of renewable energy, this plan is about as old-fashioned and dirty as it gets.

@mjrobbins

Previously – The London Fog Was a Thick Cloud of Bullshit