Scientists at the U.S. Naval Research Laboratory (NRL) are developing a process to extract carbon dioxide (CO2) and produce hydrogen gas (H2) from seawater. Then they catalytically convert the CO2 and H2 into jet fuel by a gas-to-liquids process.
The NRL effort has successfully developed and demonstrated technologies for the recovery of the CO2 and the production of the H2 from seawater using an electrochemical acidification cell, and the conversion of the CO2 and H2 to hydrocarbons that can be used to produce jet fuel.
NRL research chemist Dr. Heather Willauer said, “The potential payoff is the ability to produce JP-5 jet fuel stock at sea reducing the logistics tail on fuel delivery with no environmental burden and increasing the Navy’s energy security and independence.” JP-5 is very close chemically to kerosene and diesel.
Willauer continues, “The reduction and hydrogenation of CO2 to form hydrocarbons is accomplished using a catalyst that is similar to those used for Fischer-Tropsch reduction and hydrogenation of carbon monoxide. By modifying the surface composition of iron catalysts in fixed-bed reactors, NRL has successfully improved CO2 conversion efficiencies up to 60%.”
Technically, the NRL has developed a two-step laboratory process to convert the CO2 and H2 gathered from the seawater to liquid hydrocarbons. In the first step, an iron-based catalyst can achieve CO2 conversion levels up to 60% and decrease unwanted methane production from 97% to 25% in favor of longer-chain unsaturated hydrocarbons (olefins). Then in step two the olefins can be oligomerized (a chemical process that converts monomers, molecules of low molecular weight, to a compound of higher molecular weight by a finite degree of polymerization) into a liquid containing hydrocarbon molecules in the carbon C9-C16 range, suitable for conversion to jet fuel by a nickel-supported catalyst reaction.
The raw materials are abundant. CO2 is an abundant carbon source in seawater, with the concentration in the ocean about 140 times greater than that in air. 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. When processes are developed to take advantage of the higher weight per volume concentration of CO2 in seawater, coupled with more efficient catalysts for the heterogeneous catalysis of CO2 and H2, a viable sea-based synthetic fuel process could be developed.
The NRL effort made significant advances developing carbon capture technologies in the laboratory. In the summer of 2009 a standard commercially available chlorine dioxide cell and an electro-deionization cell were modified to function as electrochemical acidification cells. Using the novel modified cells both dissolved and bound CO2 were recovered from seawater by re-equilibrating carbonate and bicarbonate to CO2 gas at a seawater pH below 6. In addition to CO2, the cells produced H2 at the cathode as a by-product.
Note that the oceans offer a huge reserve of raw materials for fuel production.
The completed studies of 2009 assessed the effects of the acidification cell configuration, seawater composition, flow rate, and current on seawater pH levels. The data were used to determine the feasibility of this approach for efficiently extracting large quantities of CO2 from seawater. From these feasibility studies NRL successfully scaled-up and integrated the carbon capture technology into an independent skid, or “lab on a pallet’ so to speak, called a “carbon capture skid” to process larger volumes of seawater and evaluate the overall system design and efficiencies.
The carbon capture skid’s major component is a three-chambered electrochemical acidification cell. The cell uses small quantities of electricity to exchange hydrogen ions produced at the anode with sodium ions in the seawater stream. As a result, the seawater is acidified. At the cathode, water is reduced to H2 gas and sodium hydroxide (NaOH) is formed. This basic solution may be re-combined with the acidified seawater to return the seawater to its original pH with no additional chemicals. Current and continuing research using the carbon capture skid demonstrates the continuous efficient production of H2 and the recovery of up to 92% of the CO2 from seawater.
The carbon capture skid has been tested using seawater from the Gulf of Mexico to simulate conditions that will be encountered in actual open ocean processing.
The NRL group is working now on process optimization and scale-up. Initial studies predict that jet fuel from seawater would cost in the range of $3 to $6 per gallon to produce.
Willauer points out, “With such a process, the Navy could avoid the uncertainties inherent in procuring fuel from foreign sources and/or maintaining long supply lines.” During the government’s fiscal year 2011, the U.S. Navy Military Sea Lift Command, the primary supplier of fuel and oil to the U.S. Navy fleet, delivered nearly 600 million gallons of fuel to Navy vessels underway, operating 15 fleet replenishment ships around the globe.
The Navy’s fuel supply system works at sea, while underway and is a costly endeavor in terms of logistics, time, fiscal constraints and threats to national security and the sailors at sea.
It’s a brilliantly insightful use of the environment. Moreover the technology will help clean the seawater of an overcharge of CO2 and that is actually a recycling of fossil fuel additions to the environment.
Entrepreneurs are going to realize the Navy’s work could be an industrial boon to fuel production as well as shorten the carbon cycle. While the Navy thinks $3 to $6 for production cost, the private sector would very likely drive that cost far further down.
It’s not hard to imagine that in a few years most of the oil business might simply be at sea, harvesting CO2 and H2, making petroleum products from a recycling of the CO2 from the past use of fossil fuels.
Many may complain that the military is a waste, poor policy, or other notions that fly in the face of human nature. But in the past few decades the U.S. military, filled with volunteers, can make significant contributions, and now perhaps solve what has been thought to be an intractable problem.