Navy Creates Fuel From Seawater

New submitter lashicd sends news that the U.S. Naval Research Laboratory has announced a successful proof-of-concept demonstration of converting seawater to liquid hydrocarbon fuel. They used seawater to provide fuel for a small replica plan running a two-stroke internal combustion engine. "Using an innovative and proprietary NRL electrolytic cation exchange module (E-CEM), both dissolved and bound CO2 are removed from seawater at 92 percent efficiency by re-equilibrating carbonate and bicarbonate to CO2 and simultaneously producing H2. The gases are then converted to liquid hydrocarbons by a metal catalyst in a reactor system. ... NRL has made significant advances in the development of a gas-to-liquids (GTL) synthesis process to convert CO2 and H2 from seawater to a fuel-like fraction of C9-C16 molecules. In the first patented step, an iron-based catalyst has been developed that can achieve CO2 conversion levels up to 60 percent and decrease unwanted methane production in favor of longer-chain unsaturated hydrocarbons (olefins). These value-added hydrocarbons from this process serve as building blocks for the production of industrial chemicals and designer fuels."

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Re:Any chemists want to weigh in??

[omglolbah]

This article is linked in the story article. It has a lot more info on the process.

http://www.nrl.navy.mil/media/... [navy.mil]

Reading between the lines

[Michael Woodhams]

TFA was points to a 2012 press release, but it contains not much more information. They must need to supply energy to this reaction, but whether this energy is as heat, electricity or something else is unclear.

I see two uses from the point of view of the U.S. navy. One is to put one of these chemical plants in an aircraft carrier, power it with the carrier's reactor, and generate fuel for the aircraft on board. The other is to put the chemical plant on a nuclear powered supply ship, which will then transfer the fuel to non-nuclear surface ships.

From a world energy point of view, this is a way to turn non-fossil fuel power (nuclear, hydro, wind) into hydrocarbon fuel, with the overall process being carbon neutral. Burning fossil fuels to provide the energy for this process would certainly be counter productive in terms of CO2 emission and very likely economically counter productive as you'd be better chemically processing your fossil fuel instead.

By the time you're going to all of this trouble to turn electricity into fuel, it is unlikely that you'd want to run a car on it - you'd rather just have an electric car. For aircraft we really have no good alternative to hydrocarbon fuels, so it could be used here. However, on the road to a low-carbon future, we have decades worth of lower hanging fruit (notably coal power stations) before we really need to care about whether our aircraft fuels are carbon neutral.

Conspicuously missing from the articles is the energy efficiency of this process. Given the $3-$6 per gallon projected jet fuel cost, presumably the efficiency is not too bad. (I notice this number hasn't changed since 2012 which makes me suspicious that it is more guesswork than calculation.)

Re:They do.

[CodeBuster]

It's unlikely that this would obviate completely the need for external supplies of fuel. At best it would probably only marginally decrease the depletion rate of on board stocks allowing for a somewhat longer cruise before a resupply is needed. There are probably other downsides to using this system too. For example, there are parts, maintenance and possibly extra wear and tear on the reactor which now not only has to propel the ship but also power an energy intensive conversion process from seawater to jet fuel. Indeed, the initiation energy for some of those chemical reactions is quite high which probably explains why somebody isn't already doing this on a large scale for profit here on land.

Re:Just like Nuclear Fusion

[CodeBuster]

You do realize that what they're producing here is artificial jet fuel, right? It's not "biofuel" because it isn't produced by bacteria or algae or other direct biological process. No, what they're talking about here is essentially the water gas shift reaction whereby dissolved CO2 in the seawater is combined with water vapor (aka steam) and carbon monoxide (produced via this "bicarbonate" reactant?) to yield carbon monoxide, carbon dioxide and hydrogen which more heat and pressure (steam) in the presence of an iron catalyst converts these products into short chain hydrocarbons (alkenes), probably ethanes (CH3) and propanes (CH4), and from there longer chain hydrocarbons with more heat and pressure until the desired blend is cooked up, jet fuels of CH9 to CH16. However, these processes don't really transition us away from fossil fuels or at least not into something besides a hydrocarbon fuel, whether produced artificially as in this case or refined from naturally occurring crude oil that we've pumped out of the ground.

Re:Any chemists want to weigh in??

[fnj]

Bubbles will appear on each wire, the negative side is hydrogen and the positive side is oxygen

Using NaCl as you describe to make the water conductive also results in the evolution of Cl - chlorine gas - more than oxygen. If your wires are bare copper, the metal also migrates from the positive wire to the negative wire, turning the solution nasty blue-green in the process.

Some caution is advised. Chlorine gas is toxic. It was used in shells to poison troops in WW1. Of course the amount is quite slight in the experiment.

Re:"Unwanted" Methane?

[CodeBuster]

It depends upon what sort of fuel you're trying to produce. Methane can definitely be burned as a fuel, on your stove for example, but it's not a good aviation fuel. The idea here is to skip methane and go straight to ethane or propane which can be up-converted to even longer chain hydrocarbons via more heat and pressure, eventually yielding jet fuel. Artificial hydrocarbon fuels themselves are nothing new. The basic processes have been known since the early part of the 20th century, but because it's way cheaper to simply refine naturally occurring petroleum pumped out of the ground, nobody does synthetic hydrocarbons unless they have to. For example, Germany produced synthetic aviation gasoline from coal during WWII as supplies of oil were gradually cut off and South Africa produced diesel fuel from coal during the sanctions of the Apartheid era.

Re:Energy

[profplump]

Converting electricity to liquid fuel, and in particular to a liquid fuel compatible with existing infrastructure, is potentially a big win. We're working on more sustainable electricity production, but no matter how much progress we make on the front there are still lots of applications where "throw some batteries at it" isn't a viable option for power storage -- being able to produce fuel from electricity and seawater is a way to bridge that gap in energy delivery without also requiring a breakthrough in electrical storage.

Re:They do.

[Anonymous Coward]

former navy machinist mate here - theres more available space than most people realize on a carrier. we were exceptionally good space management, so that wouldnt be an issue. the reactors wouldnt have an issue with producing enough energy - the whole powerplant is built with a ton of production headroom. we would often operate with up to 1/3 of our equipment either off or idling and still be well below the energy demands of the ship, even during flight ops in combat zones. there would be a slight reduction in how long the fuel would last, maybe 20 years instead of 25. but, to have onboard aviation fuel production would be very very worth it. stress to the reactors would be minimal, theyre designed to be operated at high capacity for extended amount of time and the navy doesnt come anywhere near running them at their actual capacity - everything is designed with a LOT of headroom! youre right that it isnt a slam dunk, but it is very doable

Re:They do.

[suutar]

There has not been a working commercial plant, but there has been a working thorium reactor. Oak Ridge had one running for 15 thousand hours. But the folks running the AEC wanted plutonium, so they shut down thorium research in 1973. wikipedia [wikipedia.org] has more detail.

Re:They do.

[LWATCDR]

All current carriers also have two reactors. The first carrier the USS Enterprise had 8 reactors. The Ford's new reactors do make more power but the amount is not publicly available. We do know they make 3 times as much electrical power but that does not include the propulsion power.