Catching carbon dioxide and toxic gas with a molecular sponge
Natural gas often contains carbon dioxide and hydrogen sulfide. These acid gases can corrode equipment and damage catalysts, so they need to be removed. Hydrogen sulfide is also toxic.
A solid alternative to liquid scrubbers
Industry commonly removes these gases with liquid amine solvents. These can be corrosive and need a lot of energy to regenerate. Solid porous materials that hold gas on their surfaces offer a potentially simpler approach, because they can be used and regenerated repeatedly.
Metal-organic frameworks (MOFs) are strong candidates, but many have a weakness: moisture can damage them, and real gas streams are rarely completely dry.
What we made
We used microwaves and water-based chemistry to make a family of water-stable MOFs containing copper and a second metal, avoiding hazardous organic solvents. We compared seven different second metals, and the version with nickel performed best.
At room temperature and normal atmospheric pressure, it captured 5.91 millimoles of carbon dioxide and 5.84 millimoles of hydrogen sulfide per gram. By our calculation, that is roughly a quarter of its own weight in carbon dioxide and a fifth in hydrogen sulfide.
Its pores help to explain this. Just one gram of the material has an internal surface area of 1,877 square metres, or about seven tennis courts. It also stayed stable for at least 10 capture cycles.
Why it matters
Materials like this could help to clean up gas streams while using less energy. The method also avoids hazardous solvents, which would make it more attractive for larger-scale production. The next test would be performance in real gas mixtures over longer periods.
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