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Seawater-to-fuel NRL paper - .PDF file.
The US Navy has unveiled plans to make jet fuel out of seawater, with the help of electrochemistry and gas-to-liquid fuels technology.
Researchers at the Naval Research Laboratory (NRL) in Washington, DC, have demonstrated that it is possible to obtain CO2 and hydrogen from seawater, then convert these to hydrocarbons suitable for fuelling aircraft.
Keeping ships and aircraft fuelled is a major operation for any navy. The US Navy has 15 refuelling ships — known as oilers — and last year these delivered 600 million gallons of fuel to ships under way. Generating their own fuel would free up the ships from these logistics and make the navy less dependent on imported oil, said Nancy Willauer, a research chemist who worked on the project.
The technology uses electrochemistry to recover CO2 from seawater, where it is present at a concentration 140 times greater than in air, mostly as bicarbonate with traces of carbonate and dissolved CO2 gas (carbonic acid). The navy team developed a device called an electrochemical acidification cell, which uses ion-permeable polymer membranes and an electric current to lower the pH of the seawater. The three forms of carbon in the water exist in a state of equilibrium, and making the water more acidic alters the balance between them, making gaseous CO2 the most stable form. The cell produces hydrogen gas at its cathode as a by-product.
After demonstrating this at a small scale, the NRL team scaled it up to a skid process — a freestanding unit on a scale similar to that which might be used in the field — which can reportedly recover up to 92 per cent of the CO2 from seawater taken from the Gulf of Mexico.
Converting these two gases into hydrocarbons uses a technology similar to the Fischer-Tropsch process, which has been used for many years to make fuel from ‘synthesis gas’, a mixture of hydrogen and carbon monoxide. ‘By modifying the surface compositions of iron catalysts in fixed-bed reactors, NRL has successfully improved CO2 conversion efficiencies by up to 60 per cent,’ Willauer said.
The iron-catalysed process produces short-chain unsaturated hydrocarbons, which can then be combined to make compounds containing nine to 16 carbon atoms; treating these with a catalyst supported on porous nickel converts them into a liquid suitable as jet fuel, the researchers said.
NRL is now looking into improving the efficiency of the process and scaling it up and believes that the final process should be able to produce fuel at a price of between $3 and $6 per gallon (between fifty pence and £1 per litre). The process could be powered using nuclear electricity or by a method known as solar OTEC, which uses the natural temperature gradient between different levels of the ocean to power electricity generation, the team suggested. The research can be read in this paper.
Would one of the editors mind clarifying the quoted fuel prices as the current conversions are clearly out.
I’m not sure I understand the working behind this:
“between $3 and $6 per gallon (between £7 and £14 per litre)”
Don’t know what the previous numbers were, but it is anything but ‘corrected’ now, at $3/gal. given as equivalent to £7/L.!
A US gal. is 3.78 L. and the pound is currently worth ~ $1.60, so $3 is more like £1.25.
The costs quoted are irrelevant at present what is more important is the ability to do away with the Replenishment At Sea (RAS) system. All Navy ships need frequent re-fueling and the need to break off actions to rendezvous with RAS ships is a nuisance and very hazardous as well as making them more vulnerable to opposing forces. So taking fuels from sea water as required is a huge break through and should be applauded.
According to my calcs. it should be about 50p to 100p/L. Can someone confirm ?
Good idea. If it works REALLY well, the Navy will still need its oiler fleet though, only to offload the fuel from the aircraft carriers, not delivery it!
I think we may be looking at the future here.
Forget hydrogen and batteries – research, economics and sheer bang for buck is taking us towards the use of CO2 as the feedstock for new fuel synthesis.
If Nuclear electicity is required then the generation of synthetic fuel would be limited to the big CVN carriers. Only if they can generate an amount of fuel in excess of air group’s needs will they be able to supply other ships.
Wouldn’t it be simpler just to use the nuclear plant power output directly to drive the ship?
This sounds like something with limited application as a retrofit to existing big vessels.
“If Nuclear electicity is required then the generation of synthetic fuel would be limited to the big CVN carriers. Only if they can generate an amount of fuel in excess of air group’s needs will they be able to supply other ships.”
Given this is jet fuel they are looking at, the main users would be Carriers.
The other thing I see this as being useful for is recycling old nuclear subs as fuel generators, one way to have a less target-able fuel supply.
Shhh… don’t tell the hydrogen lobby. There all having so much fun working out how to put 700 and even 1100 bar gas cylinders in cars
Hydrogen lobby are still searching for hydrogen mines .. the idea of using hydrocarbons as an energy dense storage device (admit the re-conversion devices need work as 30-50% is not great) is way past them. Hydrogen.. fuel of the bright future.. one day they will discover methanol!
Has anyone seen an energy break down for this process.
This process is going to require a lot of energy, where are they going to get it from (nuclear power)?
There is no mention of the environmental impact this will have. CO2 levels are rising in the oceans so maybe this will be a benefit. Regardless, an impact study should also be published.
How about using offshore wind funneling power to old oil platforms? That would alleviate the inconsistent power and it’s cabling to shore. A tanker could periodically pump out the fuel.
@randydutton, why not just build the offshore wind on and around the platform and save long cables?
A fantastic way to lower atmospheric CO2 levels. Good for the environment.
Is this going to be good for the atmosphere?
The CO2 being used is desolved in the ocean, but when the jet fuel is burned it will produce CO2 in the atmosphere increasing CO2 levels and thus warming. They will need to find a way to have atmospheric CO2 absorbed into ocean and sea water.
I could not load the paper from the link, is there a login?
I do recall a lecturer telling us that he had been involved in work in the late 40s (I seem to recall the location was the BP R&D labs at Sunningdale?) to enhance petrol efficiency: that had given figures of 150/mpg: but that, by agreement between the ‘Seven Sisters’. the secrets were contained in a vault more secure than that of the Bank of England! And why not in the situation of that era?