US Navy demos recovery of CO2 and production of H2 from seawater, with conversion to liquid fuel; “Fuel from Seawater”
Researchers at the US Naval Research Laboratory (NRL), Materials Science and Technology Division have demonstrated novel NRL technologies developed for the recovery of CO2 and hydrogen from seawater and their subsequent conversion to liquid fuels. Flying a radio-controlled replica of the historic WWII P-51 Mustang red-tail aircraft (of the legendary Tuskegee Airmen), NRL researchers Dr. Jeffrey Baldwin, Dr. Dennis Hardy, Dr. Heather Willauer, and Dr. David Drab used a novel liquid hydrocarbon fuel to power the aircraft’s unmodified two-stroke internal combustion engine.
The test provides a proof-of-concept for an NRL-developed process to extract CO2 and produce hydrogen gas from seawater, subsequently catalytically converting the CO2 and H2 into fuel by a gas-to-liquids process. The potential longer term payoff for the Navy is the ability to produce fuel at or near the point of use when it is needed, thereby reducing the logistics tail on fuel delivery, enhancing combat capabilities, and providing greater energy security by fixing fuel cost and its availability.
From an environmental perspective, such a combination of integrated NRL-developed technologies could be considered CO2 neutral. The carbon dioxide, produced from combustion of the synthetic fuel, is returned to the atmosphere where it re-equilibrates with the ocean to complete the natural carbon cycle.
Using an innovative and proprietary NRL electrolytic cation exchange module (E-CEM), both dissolved and bound CO2 are removed from seawater at 92% 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.
The energy required to obtain these feedstocks from the ocean is primarily for the production of hydrogen; the carbon dioxide is a “free” byproduct. The process of both recovering CO2 and concurrently producing H2 gas eliminates the need for additional large and expensive electrolysis units.
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. 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.—Dr. Heather Willauer, NRL research chemist
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% 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% 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.
In the second step, using a solid acid catalyst reaction, these olefins can be oligomerized (a chemical process that converts monomers, molecules of low molecular weight, compounds of higher molecular weight using controlled polymerization). The resulting liquid contains hydrocarbon molecules in the carbon rang—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, the Navy researchers suggested. 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, according to the team.