This article was written by Dr Célia Sapart, Director Communications and Climate Science at CO2 Value Europe.
Today, the extraction and use of fossil carbon is the main controller of the Earth’s thermostat. To mitigate climate change, the urgency is to substitute fossil-based products and implement circular carbon solutions to generate essential goods and services.
While discussions on carbon removal are high on political agendas, we often observe a certain level of confusion between solutions to reduce CO2 emissions, avoid new emissions, or remove CO2 from the atmosphere. This does not ease the understanding of the potential and limits of either concept and may affect public and policy acceptance1. However, most of these technologies, if combined wisely, will be of significant help to reach climate targets. In this article, we discuss the role and climate impact of Carbon Capture Utilisation (CCU) technologies2.
CCU is a broad term that covers processes that aim at capturing CO2 from flue gas or directly from the air and converting it into a variety of products such as renewable fuels, chemicals, and materials. CO2 has already been used for decades with mature technologies in various industrial processes to produce e.g. beverages, fertilisers, etc. But today, numerous new CCU technologies at various stages of development and commercialisation aim at mitigating climate change3,4. These technologies have the potential to 1) reduce net CO2 emissions, 2) remove CO2 from the air, 3) provide substitutes for carbon-intensive and fossil-based products, 4) store and transport renewable energy, and 5) generate marketable products.
Temporary CO2 storage does not mean delaying emission as emissions have been avoided in the first place
CCU is often mingled with Carbon Capture and Storage (CCS) while both concepts distinctly differ. CCS consists of capturing CO2, transporting and storing it underground, while CCU is a circular approach that converts and stores CO2 into essential products5. The duration of the CO2 storage into a product strongly varies from days to centuries according to the applications. However, in contrast to CCS, CCU should not be assessed only with respect to the duration and/or capacity of storage in a product, but rather with a comprehensive life-cycle analysis of the CO2-based product generated6. If CO2 based products can be produced with lower climate impact than conventional ones or if CO2 is captured again at the end of life of the CCU products, in both cases, a climate benefit can be asserted independently of the duration of CO2 storage in the product.
CCU can allow permanent lock-in of CO2 in materials
CO2 mineralisation7, an emerging CCU pathway, allows permanent CO2 storage. This approach makes CO2 react with mineral-rich wastes to form carbonates, which are stable chemical compounds. Because it utilises the chemical energy available in the waste, this method constitutes a low energy and low cost means to reduce emissions and permanently lock CO2 into valuable building materials such as concrete, aggregates, asphalt, construction fill, etc. Based on life-cycle analysis8,9, all considered CCU technologies for mineralisation could reduce climate impacts over the entire products’ life-cycle based on the current state-of-the-art and today’s energy mix.
These CO2-based materials do not only remove CO2 from flue gas or from the air, but they can also substitute carbon-intensive products (e.g. cement). Current data8,10 suggests that up to 1/4 of the cement market could be substituted by mineralisation products which would significantly decreasing the carbon footprint of building materials at a global scale.
Moreover, when CO2 is captured directly from the air11 to become stored permanently in such a material, mineralisation can create negative emissions and thus be considered as a carbon dioxide removal (CDR) technology12.
Several carbon mineralisation technologies13,14 are already commercialised globally and the first pavement made out CO2-based bricks15 has been installed in Ghent, Belgium in 2020.
The proposed revision of the Emission Trading System16 now recognises that CO2 which is chemically and permanently bound in a product and, therefore, is not released into the atmosphere under normal use of the product – as in CO2 mineralisation – is excluded from the obligation to surrender emission allowances.
CCU is a solution to stimulate the renewable energy transition
CCU technologies, via the Power-to-X principle17, play a crucial role in supporting the clean energy transition by facilitating electricity uptake, storage and transportation. How does it work? Power-to-X means converting electricity into products or in other words storing electricity into products such as fuels and chemicals. Via this approach, synthetic hydrocarbon fuels (also called e-fuels) can be produced, using renewable electricity to generate hydrogen via the electrolysis of water, and making it react with CO2. For example, CO2 emissions from cement or steel plants can be captured and used with renewable hydrogen to produce sustainable aviation fuel18. This allows a net reduction of CO2 emissions from industrial installations and a decrease in the use of fossil resources for aviation fuels; if CO2 is captured directly from the air, this concept can also lead to net-zero emission as envisaged e.g. in the Norsk e-fuel project19 in Norway.
These CO2-based renewable fuels are drop-in solutions for hard-to-abate sectors such as aviation, shipping and energy-intensive industries. They have volumetric energy densities that are orders of magnitude above those of hydrogen, so they can be easier to transport and store; they also have the advantage of bringing renewable energy to sectors, where direct electrification is not evident, without changes in storage, distribution and use infrastructure. The surplus of renewable energy, generated when energy demand is low, could then provide an inexpensive energy supply to produce renewable fuels.
These CO2-based products are recognized under the name “Renewable Fuels of Non-Biological Origin (RFNBOs)” in the EU Green Deal legislative packages20, and their production and use in energetic and non-energetic applications is being incentivised as solutions to mitigate climate change.
While the efforts at all levels should focus at first on sober solutions and on preventing greenhouse gas emissions, CCU technologies remain impactful solutions for numerous sectors, especially for those where no other alternatives exist. The large-scale deployment of these technologies will largely depend on the development of a strongly supportive policy framework. Therefore, we welcome the recent steps taken towards this direction (e.g. Fit-for-55 package), and we call for consistent and fair recognition of CCU, when it leads to a net reduction of CO2 emissions (based on full life-cycle analysis), and when it helps to move away from fossil resources.