A big piece
of reducing carbon emissions is separating the carbon dioxide (CO2) from the emissions of fossil fuels and storing it, or using it in making other
chemicals. A "molecular sieve" is a common method for getting CO2 out
of a mix of chemicals; it's a kind of ultra-fine filter. Unfortunately such
sieves usually need more filtering to get the CO2 out -– they aren’t always specific.
At the University of Melbourne Professor Paul Webley and his team have come up with a kind of molecular sieve that pulls out CO2 only. It's a chemical called a chabazite, which has a lattice-like molecular structure. Chabazite is in a class of chemicals called zeolites, which are common in lots of industrial settings and even used in kitty litter and swimming pool filters.
The chabazite consists of a kind of ring of atoms of silicon, aluminum and oxygen, with a cesium atom in the center. The cesium atom acts like a trap door, letting carbon dioxide pass but blocking other chemicals. Webley and his team tested the chabazite in a mixture of carbon dioxide and methane -– natural gas. They also found that it worked in separating other gases such as nitrogen.
Different gases were allowed through
the trapdoor at different temperatures, so it's possible to use that property
to get even better selection of the carbon dioxide.
One of the more immediate applications
might be getting the carbon dioxide out of natural gas deposits. Often, when
drilling for natural gas, there is a lot of carbon dioxide present that has to
be taken out before the natural gas can be compressed and liquefied. The
chabazite could also improve the scrubbers used to take CO2 from emissions.
The work was published in the Journal
of the American Chemical Society.
Photo: A naturally-occurring crystal of chabazite. Credit: Wikimedia Commons