https://www.chemistryworld.com/news/selective-graphene-membranes-could-invigorate-carbon-capture-technology/3010831.article
[links and images in online article]
Selective graphene membranes could invigorate carbon capture technology
By Edward Gardner
12 August 2019
Concept shows promise as a way to sidestep the energy penalties of
numerous industrial separations
Scientists have developed membranes that separate carbon dioxide from
nitrogen. The membranes feature porous graphene decorated with polymers
and use interactions between the polymers and carbon dioxide to create a
system that can selectively filter carbon dioxide out of flue gas.
Carbon capture and storage remains one of the most promising strategies
to limit the impact of carbon emissions. Some industrial plants already
capture carbon dioxide using amine sorbents, where heating regenerates
the amines and removes the carbon dioxide – but this process is energy
intensive.
Now, scientists led by Kumar Agrawal at the Swiss Federal Institute of
Technology Lausanne (EPFL) have designed a polymer-functionalised
graphene membrane that could rival industry’s current approach and
present a more energy efficient method to filter carbon dioxide out of
industrial emissions. ‘We designed the membrane while optimising the two
aspects that are key for separation: the selective layer thickness and
the affinity for carbon dioxide,’ says Argawal.
Unlike sorbents, membranes operate in a steady state. Carbon dioxide in
the flue gas pumped onto the membrane interacts with the polymers on the
surface. These interactions build up a higher concentration of carbon
dioxide than nitrogen at the interface and the concentration difference
causes carbon dioxide to pass through the membrane’s pores. ‘In a way we
are regenerating it automatically,’ explains Argawal.
The membranes, which are much thinner than existing membranes, have a
selectivity of 22.5 and permeance of 6180 gas permeation units (GPU),
exceeding the targets of 20 and 1000 GPU set by the US Department of
Energy. This means that the membrane blocks 96% of the nitrogen in the
flue gas, yet lets through a small amount to ensure its pores aren’t
blocked off by nitrogen, which keeps carbon dioxide filtering through
quickly.
‘The most impactful aspect is the preparation of high-quality samples of
single-layer porous graphene-polymer hybrid membranes,’ comments Sankar
Nair, who researches the use of nanoporous membranes in renewable and
clean energy at Georgia Institute of Technology, US. ‘Practical
large-scale applications may have a longer way to go.’
While the team has only made centimetre-sized versions of their
membrane, Agrawal says they could ultimately alter carbon capture
technology, as well as other industrial separations. ‘If you can do it
for carbon dioxide and nitrogen, you can do it for any molecule.’
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