MIT researchers convert emissions into fuel
Tuesday, December 05, 2017
Scientists may have discovered a means by which they can transform emissions back into fuel, essentially using waste discharge to power our transportation needs, possibly in the not-too-distant future. The findings of the research were published in the journal ChemSusChem.
In the most basic of terms, the MIT-developed method converts carbon dioxide into useful compounds by using a new system that alters power plant emissions into fuel for cars, trucks and planes, as well as into chemical feedstocks for a wide variety of products.
The membrane-based system was developed by MIT postdoc Xiao-Yu Wu and Ahmed Ghoniem, the Ronald C. Crane Professor of Mechanical Engineering. The membrane, made of a compound of lanthanum, calcium and iron oxide, lets oxygen from a stream of carbon dioxide move through it to the other side, leaving carbon monoxide behind.
"Other compounds, known as mixed ionic electronic conductors, are also under consideration in their lab for use in multiple applications including oxygen and hydrogen production," MIT News reports.
The membrane, with a structure known as perovskite, allows only oxygen atoms to pass through. The separation is driven by temperatures of up to 990 degrees Celsius, and the key to making the process work is to keep the oxygen that separates from carbon dioxide flowing through the membrane until it reaches the other side. This could be done by creating a vacuum on the side of the membrane opposite the carbon dioxide stream, but that would require a lot of energy to maintain, the MIT researchers explain.
Carbon monoxide produced during this process can be used as a fuel by itself or combined with hydrogen and/or water to make many other liquid hydrocarbon fuels, as well as chemicals including methanol (used as an automotive fuel) and syngas.
The energy needed to keep the process going is heat, "which could be provided by solar energy or by waste heat, some of which could come from the power plant itself and some from other sources," the site reports. This means it's possible to store that heat in chemical form, for use whenever it's needed. Chemical energy storage has a very high energy density — the amount of energy stored for a given weight of material — as compared to many other storage forms.
The process has been demonstrated to work, but research continues to see how to increase the oxygen flow rates across the membrane. Additionally, the researchers are working to integrate the membrane into working reactors and coupling the reactor with the fuel production system.
In a natural gas power plant, for example, the incoming natural gas could be split into two streams — one that would be burned to generate electricity, producing a pure stream of carbon dioxide, while the other stream would go to the fuel side of the new membrane system, providing the oxygen-reacting fuel source.
That stream would produce a second output from the plant, a mixture of hydrogen and carbon monoxide known as syngas, which is a widely used industrial fuel and feedstock. The syngas can also be added to the existing natural gas distribution network.
If possible, and scalable, the process could be a major victory in the war to reduce carbon-based emissions and might cut the amount of fossil fuels consumed.
The research was funded by Shell Oil and the King Abdullah University of Science and Technology, and the process can work with any level of carbon dioxide concentration, but higher concentrations make the process more efficient.
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