In order to limit global warming to 1.5˚C above pre-industrial levels and avoid some of the worse impacts of climate change, it means eliminating all 42 billion tonnes of annual CO2 emissions by 2050.
One way of doing this is to cut emissions. Another is to design materials that can remove the CO2 that is already in the atmosphere or before it’s expelled. The problem is that no one has quite worked out how best to do this – yet.
The air filter system in space inspired Professor Stefano Brandani and Dr Giulio Santori from the University of Edinburgh, UK, to develop a way of capturing and concentrating CO2 directly from the atmosphere. This ambitious strategy – to build a so-called artificial tree – would see CO2 captured to be stored in large underground reservoirs.
The CO2 breathed by astronauts aboard the ISS is captured by using a sponge-like mineral called a zeolite, which has tiny pores to lock in a CO2 molecule. On the space station, the zeolites empty their CO2 when exposed to the vacuum of space.
As part of a project called ACCA, Dr Santori is hacking the system so it will work on Earth. This is more challenging. ‘There is so much more CO2 to capture and concentrations are more dilute to begin with on Earth, so it is much more energy intensive,’ he explained. ‘The starting concentration of CO2 on the ISS is one order of magnitude higher.’
The idea is to install membranes that trap CO2, which can then be concentrated and compressed for storage. ‘Membranes are efficient and can save energy compared to other systems,’ said Professor Marco Giacinti Baschetti at the University of Bologna, Italy.
In traditional strategies used by industries such as coal plants, CO2 is captured in special liquids or solid sponge-like structures, but these must then be heated up to release the CO2. This is not needed with membranes. All existing technologies, however, are costly. Current membrane materials are not durable enough and do not separate CO2 well enough to be economically sensible.
Prof. Baschetti runs a project called NANOMEMC2 which is developing a number of different membranes for CO2 capture. In November, the team is to test a new membrane in a Colacem cement facility in Italy.
Developed by project scientists at the Norwegian University of Science and Technology, the membrane is made of hollow fibres, about a millimetre thick, and covered with an extremely thin layer of nanocellulose and polymer mixed with artificial amino acids. The nanocelluose, which is made of miniscule fibres from wood, allows CO2 to permeate, while blocking other gases. The amino acid grabs onto CO2 and pulls it across the membrane.