The U.S. Naval Research Laboratory (NRL) has developed a technology for simultaneously extracting carbon dioxide and hydrogen from seawater and converting the two gases to a liquid hydrocarbon fuel, as a possible replacement for petroleum-based jet fuel.

Fueled by the liquid hydrocarbon, the research team demonstrated sustained flight of a radio-controlled P-51 replica of the legendary Red Tail Squadron, powered by an off-the-shelf, unmodified two-stroke internal combustion engine.

NRL operates a lab-scale fixed-bed catalytic reactor system and the outputs of this prototype unit have confirmed the presence of the required C 9 -C 16 molecules in the liquid.

This system is the first step towards transitioning the NRL technology into commercial modular reactor units that may be scaled-up by increasing the length and number of reactors, according to NRL research chemist Heather Willauer, PhD.

“This is the first time technology of this nature has been demonstrated with the potential for transition from the laboratory, to full-scale commercial implementation,” said Willauer.

The predicted cost of jet fuel using these technologies is in the range of $3 to $6 per gallon, and with sufficient funding and partnerships, this approach could be commercially viable within the next seven to ten years, NRL suggests.

Technical details

NRL has made significant advances in the development of a gas-to-liquids (GTL) synthesis process to convert CO 2 and H 2 from seawater to a fuel-like fraction of C 9 -C 16 molecules.

Using an NRL electrolytic cation exchange module (E-CEM), both dissolved and bound CO 2 are removed from seawater at 92 percent efficiency by re-equilibrating carbonate and bicarbonate to CO 2 and simultaneously producing H 2 .

The gases are then converted to liquid hydrocarbons by a metal catalyst in a reactor system. CO 2 in the air and in seawater is an abundant carbon resource, but the concentration in the ocean (100 milligrams per liter [mg/L]) is about 140 times greater than that in air, but 1/3 the concentration of CO 2 from a stack gas (296 mg/L). Two to three percent of the CO 2 in seawater is dissolved CO 2 gas in the form of carbonic acid, one percent is carbonate, and the remaining 96 to 97 percent is bound in bicarbonate.

In the first patented step, an iron-based catalyst has been developed that can achieve CO 2 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.