NRL is developing and demonstrating technologies that recover carbon dioxide (CO2) and produce hydrogen (H2) from seawater. These feedstocks are combined in an NRL gas-to-liquid (GTL) process to produce value added hydrocarbons. It is envisioned that these hydrocarbons will one day be used to augment industrial chemical processes and produce designer fuels (methane, methanol, and diesel and jet fuel) on land or at sea for the Navy. Synthesizing drop in replacements for petroleum-derived fuel at or near the point of use translates into “Freedom of Action for the Warfighter,” potential long term cost savings to the Navy, and achieves the Navy goals for alternative energy set forth by SECNAV. These goals require that 50 percent of DON energy requirements at sea and on shore be derived from alternative (non-petroleum) sources by 2020. These goals seek to enhance combat capabilities and provide greater energy security while having a minimal impact on the environment. From an environmental perspective, such a combination of integrated NRL 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.
Carbon Capture: Using novel and proprietary NRL electrolytic cation exchange modules (E-CEM), up to 92% of CO2 both dissolved and bound can be removed from seawater. The concentration of carbon dioxide in seawater is 140 times greater than that in air, yet harvesting large quantities of CO2 fast and efficiently from seawater had not been demonstrated prior to the recently announced patented NRL process. In addition to recovering CO2, the E-CEM HC (hydrogen and carbon dioxide) module simultaneously produces H2 gas at the cathode. The energy required to obtain these feedstocks from the ocean is primarily for the production of hydrogen and 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.
The E-CEM C (carbon dioxide) module offers the opportunity to recover only CO2 from both seawater and alkaline water sources therefore significantly reducing the overall energy requirements for the process. This second novel and proprietary technological approach is envisioned to produce only CO2 for use in a growing number of processes seeking to increase product efficiencies. These processes include enhanced biological carbon fixation and new strategies involving CO2 in Low Temperature Solidification Processes.
NRL and partners have developed a carbon capture skid shown in Figure 1 that demonstrates the continuous and efficient production of CO2 from seawater using the different E-CEM technologies. Extraction of CO2 utilizing these to two different E-CEM approaches offers a pure and concentrated source of CO2 from the environment, while reducing the effects of anthropogenic CO2 on the ocean. This unique source of CO2 is extremely advantageous when compared to CO2 recovered from flue and stack gasses. These sources require energy intensive hardware and further cost to purify the gasses to be used in any biological carbon fixation applications where pH, concentration, and purity affect the living organisms and designer fuel GTL process where purity affects the catalyst. The process efficiency, the capability to produce large quantities of H2 using the E-CEM HC module if needed, and the ability to process the seawater without the need for additional chemicals or pollutants, has made these technologies far superior to membrane and ion exchange technologies previously developed and tested for recovery of CO2 from seawater and air.
Synfuel Production: Achieving high catalytic conversion efficiencies and selectivities of CO2 and H2 to value added hydrocarbons to be used as chemicals or designer fuels is a key scientific challenge which NRL continues to study at the basic science level. NRL has made significant advances in the development of a two-step GTL process to convert CO2 and H2 from seawater to a fuel-like fraction of C9-C16 molecules. In the first patent pending 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 23 percent in favor of longer-chain unsaturated hydrocarbons (olefins). These value-added hydrocarbons are 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 range, C9-C16, suitable for use a possible renewable replacement for petroleum based jet fuel. 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 (Figure 2) in the liquid. This finished liquid hydrocarbon from carbon dioxide and hydrogen was recently used to power an internal combustion (IC) engine of a model aircraft at Blossom Point, Maryland. This lab-scale system is the first step towards transitioning the NRL technology into commercial modular reactor prototype units. In addition, we are investigating alternative GTL processes that involve CO2 and H2.