Fueling the fleet, Navy looks to the seas

Sep 24, 2012

Scientists at the US Naval Research Laboratory are developing a process to extract carbon dioxide and produce hydrogen gas from seawater, subsequently converting the gases into jet fuel by a gas-to-liquids process.

Refueling U.S. Navy vessels, at sea and underway, is a costly endeavor in terms of logistics, time, fiscal constraints and threats to national security and sailors at sea.

In Fiscal Year 2011, the U.S. Navy Military Sea Lift Command, the primary supplier of fuel and oil to the U.S. Navy fleet, delivered nearly 600 million gallons of fuel to Navy vessels underway, operating 15 fleet replenishment oilers around the globe.

From Seawater to CO2

Scientists at the U.S. Naval Research Laboratory are developing a process to extract carbon dioxide (CO2) and produce (H2) from seawater, subsequently catalytically converting the CO2 and H2 into jet fuel by a gas-to-liquids process.

"The potential payoff is the ability to produce JP-5 fuel stock at sea reducing the logistics tail on fuel delivery with no environmental burden and increasing the Navy's energy security and independence," says research chemist, Dr. Heather Willauer.

NRL has successfully developed and demonstrated technologies for the recovery of CO2 and the production of H2 from seawater using an electrochemical acidification cell, and the conversion of CO2 and H2 to hydrocarbons ( consisting of hydrogen and carbon) that can be used to produce jet fuel.

"The reduction and of CO2 to form hydrocarbons is accomplished using a catalyst that is similar to those used for Fischer-Tropsch reduction and hydrogenation of carbon monoxide," adds Willauer. "By modifying the of iron catalysts in fixed-bed reactors, NRL has successfully improved CO2 conversion efficiencies up to 60 percent."

A Renewable Resource

CO2 is an abundant carbon (C) resource in the air and in seawater, with the concentration in the ocean about 140 times greater than that in air. Two to three percent of the CO2 in seawater is dissolved CO2 gas in the form of carbonic acid, one percent is carbonate, and the remaining 96 to 97 percent is bound in bicarbonate. If processes are developed to take advantage of the higher weight per volume concentration of CO2 in seawater, coupled with more efficient catalysts for the heterogeneous catalysis of CO2 and H2, a viable sea-based synthetic fuel process can be envisioned. "With such a process, the Navy could avoid the uncertainties inherent in procuring fuel from foreign sources and/or maintaining long supply lines," Willauer said.

NRL has made significant advances developing carbon capture technologies in the laboratory. In the summer of 2009 a standard commercially available chlorine dioxide cell and an electro-deionization cell were modified to function as electrochemical acidification cells. Using the novel cells both dissolved and bound CO2 were recovered from seawater by re-equilibrating carbonate and bicarbonate to CO2 gas at a seawater pH below 6. In addition to CO2, the cells produced H2 at the cathode as a by-product.

These completed studies assessed the effects of the acidification cell configuration, seawater composition, flow rate, and current on seawater pH levels. The data were used to determine the feasibility of this approach for efficiently extracting large quantities of CO2 from seawater. From these feasibility studies NRL successfully scaled-up and integrated the carbon capture technology into an independent skid to process larger volumes of seawater and evaluate the overall system design and efficiencies.

The major component of the carbon capture skid is a three-chambered electrochemical acidification cell. This cell uses small quantities of electricity to exchange hydrogen ions produced at the anode with sodium ions in the seawater stream. As a result, the seawater is acidified. At the cathode, water is reduced to H2 gas and sodium hydroxide (NaOH) is formed. This basic solution may be re-combined with the acidified seawater to return the seawater to its original pH with no additional chemicals. Current and continuing research using this carbon capture skid demonstrates the continuous efficient production of H2 and the recovery of up to 92 percent of CO2 from seawater.

Located at NRL's Center for Corrosion Science & Engineering facility, Key West, Fla., (NRLKW) the skid has been tested using seawater from the Gulf of Mexico to simulate conditions that will be encountered in an actual open ocean process for capturing CO2 from seawater and producing H2 gas. Currently NRL is working on process optimization and scale-up. Once these are completed, initial studies predict that jet fuel from seawater would cost in the range of $3 to $6 per gallon to produce.

How it Works: CO2 + H2 = Jet Fuel

NRL has developed a two-step process in the laboratory to convert the CO2 and H2 gathered from the to liquid hydrocarbons. In the first step, an iron-based catalyst has been developed that can achieve CO2 conversion levels up to 60 percent and decrease unwanted methane production from 97 percent to 25 percent in favor of longer-chain unsaturated hydrocarbons (olefins).

In the second step these olefins can be oligomerized (a chemical process that converts monomers, molecules of low molecular weight, to a compound of higher molecular weight by a finite degree of polymerization) into a liquid containing hydrocarbon molecules in the carbon C9-C16 range, suitable for conversion to jet fuel by a nickel-supported catalyst reaction.

Explore further: Home cheap home: Vietnam architect's quest for low-cost housing

add to favorites email to friend print save as pdf

Related Stories

Shells slim down with CO2

Aug 09, 2011

Marine algae that turn carbon dissolved in seawater into shell will produce thinner and thinner shells as carbon dioxide levels increase.

Recommended for you

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Sep 24, 2012
Where does the energy for this process come from, since it's obviously endothermic?


The ship's on-board nuclear power plant?

Nothing else makes sense...

I can see how using the nuclear reactor to power this reaction would make sense, because it's always there and the vessel is often parked for long periods of time anyway.

Maybe I'm an idjit and need to learn something, or maybe they need to do a better job explaining this process.

Still, not needing a tanker to bring in more fuel would be a huge strategic and tactical advantage because you have fewer "soft targets" involved in your supply chains.
5 / 5 (1) Sep 24, 2012
Since they are talking about making JP-5 jet fuel and all American aircraft carriers are nuclear powered it would be the on-board nuclear power plants (plural) providing the energy.
Also, as they could make their own jet fuel they would have the advantage of not having to store as much, either making the carrier lighter and a bit quicker or allowing them to carry more armaments, armor or aircraft.
not rated yet Sep 24, 2012

Yes nuke is the only real way a moving ship can do this. Though wind could too on land or as a sailing ship with a prop/turbine in the water extracting the energy.

I though of this a long time ago as I saw the US in so many oil wars and the only way the Navy can keep operating as oil prices go through the roof.

A small 35 MW nuke like a inherently safe Hyperion style that can run the ship propulsion, house needs for cruising making fuel with power left over, on station or in port making fuel.

I'd likely go with coal or biomass as the carbon source as a little can make a lot of fuel. I'd go with some of the lighter HC's like higher gasolines as easier, less energy, C, needed to make.
5 / 5 (1) Sep 24, 2012
A typical US nuclear carrier has ~200 MW of power available and only rarely is all of the power used for propulsion. Diverting even 10% of that power under cruise conditions would be more than enough to keep all planes and auxiliary ships supplied with fuel.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.