Researchers at the US Naval Research Laboratory (NRL), Materials Science and Technology Division, have demonstrated proof-of-concept of NRL technologies developed for the recovery of carbon dioxide (CO2) and hydrogen (H2) from seawater and conversion to a liquid hydrocarbon fuel, according to the US Navy.
"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."
Last week, the Navy announced the research team had demonstrated the technology by fueling and flying a radio-controlled P-51 replica of the Red Tail Squadron — powered by an off-the-shelf, unmodified two-stroke internal combustion engine — with the seawater-derived hydrocarbon fuel, in September.
Since the success of the demonstration, the Navy says NRL scientists are now upscaling to a commercial channel reactor, to increase fuel output and obtain technical information that will be used for future scale-up and design.
According to the Navy, the two-step process involves “a proprietary NRL electrolytic cation exchange module (E-CEM), [with which] 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.”
CO2 in the air 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). NRL has made significant advances in its 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 of up to 60 percent and decrease unwanted methane production in favor of longer-chain unsaturated hydrocarbons (olefins). The Navy says the value-added hydrocarbons from this process serve as building blocks for the production of industrial chemicals and designer fuels.
In the second step, the olefins can be converted to compounds of a higher molecular level through controlled polymerization; the resulting liquid contains hydrocarbon molecules in the C9-C16 carbon range, suitable for potential use as a renewable replacement for petroleum-based jet fuel.
The Navy says the process efficiencies, along with the ability 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. The predicted cost of jet fuel using these technologies is in the range of $3-6 per gallon, and with sufficient funding and partnerships, the Navy says this approach could be commercially viable within the next seven to ten years.
Other recent, potential game-changing innovations in gas-conversion technologies include a wastewater-cleaning process developed by GE Power & Water and South African chemical and energy company Sasol, which produces a methane-rich biogas; and Newlight Technologies’ process of capturing carbon molecules from methane gas and turning them into plastic.
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