A new membrane technology developed at Newcastle University harnesses the humidity to efficiently capture carbon dioxide and may turn out to be of very high value in direct air capture for a sustainable fight against climate targets.
In a 2015 article, direct air capture was listed among the ‘Seven chemical separations to change the world’. The rationale for this ranking is that while carbon dioxide is responsible for the majority of climate change, we emit ~40 billion tonnes into the atmosphere annually; the concentration of carbon dioxide in air is very dilute ~0.04%, making its separation especially challenging.
Challenges of Separating Carbon Dioxide
According to Prof Ian Metcalfe, Royal Academy of Engineering Chair in Emerging Technologies in the School of Engineering at Newcastle University, UK, who led this research, “Dilute separation processes are the most challenging separations to perform for two key reasons. First, due to low concentration, the kinetics, that is, the speed of chemical reactions targeting the removal of the dilute component, are very slow. Second, concentrating the dilute component requires a lot of energy.”.
These are the two challenges that the Newcastle researchers, along with colleagues at the Victoria University of Wellington, New Zealand, Imperial College London, UK, Oxford University, UK, Strathclyde University, UK, and UCL, UK, set out to address with their new membrane process. The energy challenge was overcome by using naturally occurring humidity differences as a driving force for pumping carbon dioxide out of air. Additionally, the presence of water also accelerated the transport of carbon dioxide across the membrane, thereby overcoming the kinetic challenge.
Advancements in Membrane Technology
The work is published in Nature Energy and Dr Greg A. Mutch, Royal Academy of Engineering Fellow in the School of Engineering, Newcastle University, UK explains, “Direct air capture will be a key component of the energy system of the future. It will be needed to capture the emissions from mobile, distributed sources of carbon dioxide that cannot easily be decarbonized in other ways.”.
“In our work, we report the first artificial membrane that captures carbon dioxide from air and can concentrate it without energy input from a traditional source, such as a heat or pressure gradient. I think a helpful analogy might be a water wheel on a flour mill. Whereas a mill uses the downhill transport of water to drive milling, we use it to pump carbon dioxide out of the air.”
Separation Processes
Indeed, most facets of modern life are underpinned by separation processes. From what we eat, through the medicines we use, to the fuels or batteries in our car, most products that we have close at hand have passed through several separation processes. On the other hand, it is an important process in reducing waste and the need for environmental remediation by direct air capture of carbon dioxide.
While separation processes have usually been at the core of chemical manufacturing, they will assume a larger role in a circular economy world. Here, direct air capture may provide carbon dioxide as a feedstock for the fabrication of many of the hydrocarbon products of our daily lives, but now in a carbon-neutral or even carbon-negative cycle.
Most importantly, direct air capture joins an energy transition to renewables and conventional point-source carbon capture at power plants, also necessary for ambitious climate objectives, which include the Paris Agreement’s 1.5 ºC goal.
Humidity-Driven Carbon Capture
Dr. Evangelos Papaioannou, Senior Lecturer within the School of Engineering, Newcastle University, UK, explained, “Departing from conventional membrane operation, and as described in the research paper, the team tried a new carbon dioxide-permeable membrane under a range of different humidity differences applied across the membrane. As the humidity was higher at the output side, the membrane spontaneously pumped carbon dioxide into that output stream.”.
Collaborative Efforts and Future Directions
Working with collaborators at UCL and the University of Oxford, they precisely characterised the structure of the membrane using X-ray micro-computed tomography, which ultimately allowed them to make robust performance comparisons with other state-of-the-art membranes.
A key aspect of the work was in modeling the processes occurring in the membrane at the molecular scale. Using density-functional-theory calculations with a co-author now affiliated both with Victoria University of Wellington and Imperial College London, the researchers discovered ‘carriers’ inside the membrane. The carrier uniquely transports both carbon dioxide and water but nothing else. Water is required in order to release carbon dioxide from the membrane, and carbon dioxide is needed to release water. Hence, the energy from a difference in humidity drives carbon dioxide through the membrane from a low to a higher concentration.
Prof Metcalfe adds, “This was a real team effort over several years. We are very grateful for the contributions from our collaborators, and for the support from the Royal Academy of Engineering and the Engineering & Physical Sciences Research Council.”
It’s a membrane technology that may just hold the key to unlocking a new frontier in efficient direct air capture systems. The membrane, exploiting differences in natural humidity, acts like a shuttle that whisks carbon dioxide out of the air without traditional, energy-intensive processes using heat or pressure. This approach will help not only in the intrinsic energy challenge of separating dilute components such as carbon dioxide from air but also in improving transport kinetics, thus making the process more efficient and viable on a larger scale.
This technology, however, bears much deeper implications than climate mitigation efforts. According to Dr. Greg A. Mutch, the role which direct air capture will play towards the future energy landscape will be poignant for the capturing of highly mobile and distributed sources of emissions that other means cannot decarbonize. This can enable the achievement of global climate targets—which the Paris Agreement enshrines by demanding severe reductions in GHG emissions to keep the rise in global temperatures at 1.5 degrees Celsius above pre-industrial levels.
Such membranes’ ability to transport carbon dioxide selectively in the presence of other gases underlines their use in a variety of applications that could fit into a circular economy. For example, captured carbon dioxide can be used as a feedstock for the production of hydrocarbon products, so this would be a carbon-neutral or negative cycle. This could just open up a whole avenue of sustainable manufacturing and lessen the burden on fossil resources, therefore contributing to broader environmental goals beyond the reduction of emissions.
This collaborative research effort further underlines the fact that complex environmental challenges require equally collaborating interdisciplinary approaches. This work was contributed to by several institutions spread over the UK and New Zealand; it has not only progressed the underpinning membrane technology involved but also incorporated advanced characterization techniques together with theoretical modeling to optimize performance. Only through this kind of collaboration can boundaries of scientific discovery be pushed and innovative solutions brought to application quickly and with maximum effect.
In the future, further research and development in membrane technology and direct air capture will be needed. That will involve increasing production volumes and optimizing efficiency while assessing the possibility of its integration into other industrial processes. Technologies like what Newcastle University has developed will become very important in realizing a time when carbon dioxide emissions are effectively managed and reduced globally.
Reference: “Separation and concentration of carbon dioxide from air using a humidity-driven molten-carbonate membrane” by I.S. Metcalfe, G.A. Mutch, E.I. Papaioannou, S. Tsochataridou, D. Neagu, D.J.L. Brett, F. Iacoviello, T.S. Miller, P.R. Shearing, P.A. Hunt, 19 July 2024, Nature Energy.
DOI: 10.1038/s41560-024-01588-6
Source: https://scitechdaily.com/
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