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Polymers are being more selective these days about what gases can pass through them, thanks to some U.K. scientists.
The standard for polymer membranes was either to allow gases through slowly because of their low permeability or not be very
selective by not stopping one gas as another passes through. This lack of utility means that gas separation could be cheaper and use less energy if polymer membranes were both permeable and highly selective, reports ScienceDaily.
selective by not stopping one gas as another passes through. This lack of utility means that gas separation could be cheaper and use less energy if polymer membranes were both permeable and highly selective, reports ScienceDaily.
To separate gases, nonporous and porous polymer membranes may be used. With nonporous membranes, the vapors and gases are separated by their different solubility and diffusive qualities in the polymers. Small molecules move along polymer chains, influenced by local gaps of polymer segments.
With porous membranes, a pore diameter is typically about 50 nm. Different gases can pass through the pores at different rates, depending on their mass. For example, hydrogen diffuses four times faster than oxygen.
Scientists from Cardiff University’s School of Chemistry have produced a polymer that efficiently separates gas mixtures based on the different sizes of gas molecules. ScienceDaily reports further how the polymer is effective:
The polymer’s molecular structure is very contorted so that it cannot fill space efficiently, therefore leaving gaps for small gas molecules to move through quickly. However, the transport of larger gas molecules is hindered by the polymer’s extreme rigidity so that it acts as an efficient molecular sieve.
The membranes in the innovation are highly permeable to gases, but are selective for smaller gases, such as hydrogen and oxygen, over larger gases, such as nitrogen and methane. The university is applying for a patent protecting the polymerization process.
Gas separation is important for industrial processes, such as when nitrogen or oxygen need to be separated and isolated from air. Gas separation also is useful for purifying natural gas or hydrogen.
Neil McKeown, a member of the university’s research team, says:
The preparation of this highly rigid and contorted polymer required us to develop a new polymerization reaction. In fact we used some very old chemistry — the formation of Tröger’s base, which is a compound that was first prepared 125 years ago. This simple chemistry allows us to prepare highly rigid ladder polymers of high molecular mass from readily available starting materials. In addition to making polymers for efficient gas separation membranes, we anticipate that this new process will be useful for preparing polymers for a variety of different applications.
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