Researchers at MIT have developed a new membrane system that could be used to convert power plant CO2 emissions into fuel for cars, trucks and planes, as well as into chemical feedstocks for a variety of products. Funded by Shell Oil and the King Abdullah University of Science and Technology, the breakthrough is the work of MIT postdoc Xiao-Yu Wu and Ahmed Ghoniem, the Ronald C. Crane Professor of Mechanical engineering, and is detailed in a paper in the journal ChemSusChem.
The system is based on a series of membranes made of a compound of lanthanum, calcium and iron oxide, which allows oxygen from a stream of carbon dioxide to migrate through, leaving carbon monoxide behind. This carbon monoxide can then be used as a fuel or combined with hydrogen and/or water to make other liquid hydrocarbon fuels as well as chemicals such as methanol and syngas. Researchers believe that the technology could transform emissions into a feedstock and play an instrumental role in mitigating global warming if applied to electricity production.
According to Wu, the separation is driven by temperatures of up to 990 degrees Celsius and a stream of fuel such as hydrogen or methane that draws oxygen atoms through the membrane. Though energy intensive, a vacuum system could also be put into place to achieve a similar effect. In either the case, Wu and Ghoniem’s membrane prevents oxygen from migrating back and recombining with carbon monoxide, thus forming carbon dioxide.
Renewable energy such as solar or waste heat could be used to drive the process, which ultimately allows for the storage of heat in chemical form.
While Wu and Ghoniem have proven that the process works, research is ongoing to increase oxygen flow rates across the membrane, which researchers say could be done by using different materials to build the membrane, changing the geometry of the surfaces or adding catalyst materials on the surfaces. Work is also being done to integrate the membranes into operational reactors and coupling them with the fuel production system. The scalability of the system, in addition to its costs and effects on power plant operations is currently being explored.
A recent pilot project at a natural gas power plant revealed that incoming natural gas could be split into two streams, one that would be burned to produce electricity and a pure stream of CO2 and the other would go to the fuel side of the membrane system to provide an oxygen-reacting fuel source. This second stream would produce syngas — a mixture of hydrogen and carbon monoxide — for use as industrial fuel or feedstock, thereby producing additional revenue for the plant.
Wu says the system can work with any level of CO2 concentration, though higher concentrations result in a more efficient process.