Flying a radio-controlled replica of the historic WWII P-51 Mustang red-tail aircraft — of the legendary Tuskegee Airmen — NRL researchers (l to r) Dr. Jeffrey Baldwin, Dr. Dennis Hardy, Dr. Heather Willauer, and Dr. David Drab (crouched), successfully demonstrate a novel liquid hydrocarbon fuel to power the aircraft's unmodified two-stroke internal combustion engine. The test provides proof-of-concept for an NRL developed process to extract carbon dioxide (CO₂) and produce hydrogen gas (H₂) from seawater, subsequently catalytically converting the CO₂ and H₂ into fuel by a gas-to-liquids process. Credit: U.S. Naval Research Laboratory.

Fueled by a liquid hydrocarbon — a component of NRL's novel gas-to-liquid (GTL) process that uses CO₂ and H₂ as feedstock — the research team demonstrated sustained flight of a radio-controlled (RC) P-51 replica of the legendary Red Tail Squadron, powered by an off-the-shelf (OTS) and unmodified 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.

"In close collaboration with the Office of Naval Research P38 Naval Reserve program, NRL has developed a game changing technology for extracting, simultaneously, CO₂ and H₂ from seawater," said Dr. Heather Willauer, NRL research chemist. "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."

CO₂ 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, and 1/3 the concentration of CO₂ from a stack gas (296 mg/L). 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.

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.

E-CEM Carbon Capture Skid. The E-CEM was mounted onto a portable skid along with a reverse osmosis unit, power supply, pump, proprietary carbon dioxide recovery system, and hydrogen stripper to form a carbon capture system. Credit: U.S. Naval Research Laboratory.

In the second step these olefins can be converted to compounds of a higher molecular using controlled polymerization. The resulting liquid contains hydrocarbon molecules in the carbon range, C₉-C₁₆, suitable for use a possible renewable replacement for petroleum based jet fuel.

The predicted cost of jet fuel using these technologies is in the range of $3-$6 per gallon, and with sufficient funding and partnerships, this approach could be commercially viable within the next seven to ten years. Pursuing remote land-based options would be the first step towards a future sea-based solution.

The minimum modular carbon capture and fuel synthesis unit is envisioned to be scaled-up by the addition individual E-CEM modules and reactor tubes to meet fuel demands.

NRL operates a lab-scale fixed-bed catalytic reactor system and the outputs of this prototype unit have confirmed the presence of the required C₉-C₁₆ molecules in the liquid. This lab-scale 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.

The process efficiencies and the capability to simultaneously produce large quantities of H₂, and process the seawater without the need for additional chemicals or pollutants, has made these technologies far superior to previously developed and tested membrane and ion exchange technologies for recovery of CO₂ from seawater or air.

Navy researchers demonstrate proof-of-concept in first flight of an internal combustion powered model aircraft fueled by a novel gas-to-liquid process that uses seawater as carbon feedstock.