|Process flow diagram for CO2 capture and recovery based on the Green Freedom electrolytic stripping process. Click to enlarge.|
Researchers at Los Alamos National Laboratory have developed a process—called Green Freedom—for large-scale production of carbon-neutral, sulfur-free fuels and organic chemicals from air and water. The primary targets for the Green Freedom fuels are vehicles and aircraft.
Green Freedom consists of two major components: syngas (synthesis gas) production and syngas conversion. The innovation of the new process resides primarily in the method for the production of the syngas; Green Freedom relies on commercially available technology to convert the resulting syngas into product.
The primary components of Green Freedom’s syngas production are:
Carbon-dioxide capture and recovery. A newly-developed process for capture and recovery of atmospheric carbon dioxide that also produces hydrogen as a byproduct is the core of Green Freedom. The new stripping process requires about 96% less energy than a conventional thermal-stripping process.
Supplemental hydrogen production.
Carbon-neutral power source.
While the chemistry of capturing carbon dioxide from the atmosphere can be straightforward (CO2 is readily absorbed into a potassium carbonate solution where it forms bicarbonate ions), the challenge in developing a practical system lies in the large volumes of air that would need to be processed to capture sufficient amounts of CO2 for useful application. Furthermore, according to the Los Alamos team, the conventional processing can only capture 73% of the carbon dioxide from the processed air on a single pass.
By contrast, Green Freedom uses a newly-developed electrolytic stripping process that can capture production quantities of air; capture more than 95% of the carbon dioxide on a single pass; and produces hydrogen as a byproduct that reduces supplemental hydrogen production requirements by 33%.
The new electrolytic stripping process consumes about 410 kJ/mole CO2 of electricity and about 100 kJ /mole CO2 of low-level heat energy. Taking a credit for the supplemental hydrogen production avoidance, the net electrical energy consumption is about 55 kJ/mole CO2 recovered.
The supplemental hydrogen production can be based on any water-splitting technology. For the baseline process design, the team chose water electrolysis. Green Freedom also assumes a carbon-neutral power source to assist production. The Los Alamos studies used nuclear power in its analysis.
|Conceptual diagram of the production of gasoline from air and water. Click to enlarge.|
For the baseline conversion process, Los Alamos used methanol synthesis and the ExxonMobil MTG (methanol-to-gasoline) process. (Earlier post.) However, Green Freedom can also use other processes, such as a Fischer-Tropsch process to produce jet and diesel fuels.
Initial system and economic analyses indicate that the prices of Green Freedom commodities would be either comparable to the current market or competitive with those of other carbon-neutral, alternative technologies currently being considered.—F. Jeffrey Martin, principal investigator
In addition to the new electrochemical separation process, the Green Freedom system can use existing cooling towers, such as those of nuclear power plants, with carbon-capture equipment that eliminates the need for additional structures to process large volumes of air. The primary environmental impact of the production facility is limited to the footprint of the plant. It uses non-hazardous materials for its feed and operation and has a small waste stream volume.
The concept’s viability has been reviewed and verified by both industrial and semi-independent Los Alamos National Laboratory technical reviews. The next phase will demonstrate the new electrochemical process to prove the ability of the system to both capture carbon dioxide and pull it back out of solution. An industrial partnership consortium will be formed to commercialize the Green Freedom concept.
Several other CO2 to fuel projects have been announced recently, including:
A UOP and USC partnership to develop a process for the production of methanol, DME and other chemicals from carbon dioxide. (Earlier post.)
A Sandia National Laboratories effort on extending the work on the development of a device for the solar thermochemical production of hydrogen from the splitting of water to recycling CO2 into liquid hydrocarbon fuels—“Sunshine to Petrol” (S2P). (Earlier post.)
A Georgia Tech concept for the mobile on-board capture of carbon dioxide and the subsequent centralized reprocessing of the carbon dioxide to synthetic fuel. (Earlier post.)