Introduction

Carbon capture and storage (CCS) remains a hot topic around the world as pressure mounts upon big businesses to address their impact on climate change. In particular, a number of high profile individuals and companies have recently announced a huge investment in CCS. For example, Elon Musk has pledged $100m as part of global prize to demonstrate large-scale CO2 removal1 and Exxon Mobil has created its own dedicated Low Carbon Solutions business, with plans to invest $3 billion through to 2025.2

Some companies have even made explicit commitments to go beyond zero carbon emissions and pursue negative carbon emissions. For example, Microsoft has committed to removing all its historic carbon emissions by 2050.3 While green technologies have become more advanced over recent years, achieving such grand targets is likely to require a significant amount of innovation. This thought was echoed by the European Patent Office, which has its own plans to be carbon neutral by 2030,4 in a combined report with the International Energy Agency published recently.5,6 It also seems inevitable that companies are going to need to start removing the CO2 already present in the atmosphere, in addition to preventing new carbon emissions.

Direct Air Capture

Technologies for directly removing CO2 from the atmosphere, often referred to as Direct Air Capture (DAC) technologies, have been contemplated for a while and there are now various small-scale pilot plants in operation. The designs typically involve using large fans to pull untreated air through a filtration system, in which the CO2 is selectively removed. The captured CO2 is then released as a pure CO2 stream and the filtration system is regenerated. The pure CO2 can either be sustainably stored (e.g. through reaction with basalt rock7) or utilised for other applications (e.g. plastic generation, bio-fertilizers, synthetic fuels, or even to carbonate soft drinks). Possible filtration systems include:

  • reacting aqueous alkali/alkali-earth metal hydroxides with CO2 to precipitate the corresponding alkali/alkali-earth metal carbonate;8-9
  • carbonating solid inorganic bases such as calcium oxide;10
  • using alkali metal carbonates impregnated within porous matrices;11 or
  • using amines that are actively bound within porous substrates12-13 (this taking inspiration from the amine-based solutions currently being used for removing CO2 from the flue streams produced by commercial power plants).

However, building a large-scale and commercially viable DAC system poses significant challenges. Key difficulties include the low concentration of CO2 in air, the practical implications of designing a suitable filtration system, and the energy-intensive nature of the regeneration of the filtration system, meaning that clever design is required to ensure that it functions without generating more CO2 than is captured (e.g. by connecting the system to an existing waste heat source). Despite these difficulties, with an increase in funding for research in the area and a number of dedicated carbon removal companies now expanding their operations, it appears that this technology may soon start to be used on a more appreciable scale.

Has there been an increase in innovation?

A good way to monitor commercially relevant research and development is to study the trends in patent applications published in a particular technological field. Figure 1a shows the number of patent applications directed to carbon capture technology published over the last 10 years. This graph suggests that the number of new advances year on year in CCS has remained relatively consistent. However, if we look at the relative proportion of the patent applications that mention air capture, there has been more than a three-fold increase over this period (Figure 1b). This suggests that innovation in CCS is shifting to become targeted at this much tougher, but highly attractive, goal.

Figure 1a). Number of published patent applications that were tagged with CPC code Y02C20-40 (capture or disposal of greenhouse gases, specifically CO2) at the USPTO (green), CNIPA (orange), WIPO (grey) and EPO (yellow). Figure 1b). Percentage of the total publications which also contain the keyword “air” near the keyword “captur*”.

Is the technology commercially viable?

A number of companies dedicated to DAC now exist and are looking to commercialise the technology. More encouragingly, these companies seem to have recently gained traction in the market. For example, Climeworks, which uses solid absorbents and claims the world’s first commercial DAC plant14, has recently started work on a large-scale plant in Iceland15 and has also been selected to form part of Microsoft’s carbon removal portfolio to help achieve its target of negative emissions;16 Global Thermostat, which employs amine-based sorbents bound to porous substrates, has recently expanded its agreements with ExxonMobil following a successful technical evaluation;17 and Carbon Engineering, which employs the aqueous metal hydroxide approach, has joined forces with Pale Blue Dot Energy to develop plans to deploy DAC technology in the UK.18

Conclusion

In summary, DAC appears to be a rapidly developing field that could soon be offering large-scale solutions to mitigate climate change. We therefore expect that the number of patent applications directed to DAC technology will continue to increase and we look forward to monitoring the next set of developments in this increasingly important research area.