A journey to advancing carbon capture technology
The carbon capture and storage (CCS) landscape is now changing rapidly and strategies for tackling global warming have been launched on national and international levels. As COP27 and the latest United Nations report on the catastrophic consequences of failing to curb greenhouse emissions highlight, the urgency is felt globally.
The USA has now re-joined the Paris Agreement and recently announced that it aims to, at minimum, halve its greenhouse gas emissions by the end of the decade. Europe has moved from 80% reduction targets in greenhouse gas emissions by 2050 to a net zero target. Half of the nations of the world have signed up to this net zero target but it is going to be very hard to reach without changes in CCS technologies.
The question we should really be asking is ‘how is this going to be achieved?’
While there are ways to achieve this target, starting with the immediate reduction of emissions, it is unlikely that certain industries will ever be truly CO2 neutral, which means that other industries will need to be CO2 negative in order to ‘balance the books’.
Power generators, like Drax in the UK, could well be able to operate as carbon negative with Bioenergy with carbon capture, use and storage (BECCS) Technology.
There are around 20 industrial plants (and only two power stations) operating CCS at present, with a total capacity of about 40 million tonnes of CO2 /yr. Whilst this is set to double in the next few years, a large CCS plant takes up to a decade to build, and 1.5 Gigatonnes per year capture are needed (an increase of up to 40 times the current rates) by 2030 to stay on current climate trajectories. However, this carries the risk of forcing industry to focus too much on existing technologies that are available now, rather than developing potentially far superior technologies that are on the near horizon.
One such promising technology uses solid sorbents to provide a surface for CO2 to ‘stick’ to, offering significant advantages over current strategies. The main advantage is all in the ‘sticking’ process – it requires little energy, saving costs and cutting its environmental impact.
Looking forwards, we need to see some very efficient solid sorbent technologies in the near term if they are to have a chance of being part of the CCS landscape in the next 10 years. All current roadmaps describe a need for rapid development and scale-up of next generation capture technologies.
"Sustainable and practical carbon-negative technologies are not only possible, they will be necessary in achieving future carbon neutral targets."
It’s all about surface area. Effective CO2 removal from a flue gas stream requires a lot of surface on which the CO2 can be temporarily stored, without taking up too much space. One type of solid sorbent, Metal Organic Frameworks (MOFs), can do just this, with very high surface areas of up to 15,000 m2/g. To put this in context, that would mean fitting the surface area of the main campus of the University of Nottingham in a coffee cup. It may come as a surprise, therefore, that MOFs are actually relatively ‘simple’ materials, made up of just a metal ion centre and, usually, an organic ‘add-on’ – think, a 2-piece Lego set. This simple structure doesn’t mean its efficiency is compromised; we can tailor MOFs to soak up specific molecules, such as CO2.
You are probably now thinking, ‘what’s the catch?’. Why aren’t we using these wonder materials already? There is one catch that has (very) effectively held back their use in real world applications: Cost. They are tricky to make, and most manufacturers can still only make small amounts. As such, they can cost several thousand pounds per kilogram. For effective use in industry, several tons would be needed, which has so far made MOFs remain a pipedream.
Individual pellets of Aluminium Fumarate MOF (>1000m2/g) made at the university, each with the surface area of two tennis courts i.e. a total surface of ~500m2!
There are, however, reasons to be optimistic. In partnership with the Faculty of Engineering, Promethean Particles were the first to show that MOFs could be produced continuously, cost effectively and at scale. To put capacity in context, the Promethean plant can annually produce over 3 trillion m2 of surface area which equates roughly to the surface area of India. This material would effectively pack 18 London buses. In addition, they are now able to manufacture many of these MOFs using water as the solvent medium.
Promethean and the University of Nottingham have partnered with Drax to trial this pioneering bioenergy with carbon capture and storage (BECCS) process at its North Yorkshire power station.
This enables us to demonstrate that MOFs can perform well in real conditions and be manufactured at scale and in a cost effective and environmentally friendly way.
The COP27 conference will inevitably lead to a renewed focus on technologies for reducing CO2 in the atmosphere by Direct Air Capture (DACS) or BECCS. This project will be generating new data at just the right time.
UN Emissions Gap Report
The Emission Mission
Recent advances in gas storage and separation using metal–organic frameworks. Hao Li,Kecheng Wang,Yujia Sun,Christina T. Lollar,Jialuo Li,Hong-Cai Zhou Materials Today (2018).
Instant MOFs: continuous synthesis of metal-organic frameworks by rapid solvent mixing, M. Gimeno-Fabra, A.S. Munn, L.A. Stevens, T.C. Drage, D.M. Grant, R.J. Kashtiban, J. Sloan, E. Lester, R.I. Walton, Chem. Commun., 48 (2012) 10642-10644.