In 2022, no fewer than 40.6 billion tonnes of CO2 were emitted globally*. Given such a figure, the some 230 million tonnes of CO2 used annually may seem negligible. But things change and a CO2 recovery sector is beginning to emerge, with its sights set on the production of synthetic fuels, chemical products and construction materials.
As of today, carbon dioxide (CO2) is primarily used to produce urea, used as a fertiliser (130 Mt, or 57%) and to assist with enhanced oil recovery (80 Mt, or 34%). Other use (almost 10%) essentially splits between the agrifood industry (sparkling water, improving yield from greenhouses) and metal processing.
Three routes to CO2 recovery
CO2 can be used directly – as it has been since the 1970s – for enhanced oil recovery. It is equally applicable in deep geothermal energy (where it is used to bring up hot water), this method offering good potential in France which has recently decided to accelerate the sector. CO2 is also used in other niche applications, such as food packaging, wine growing, water treatment, refrigeration or welding.
Another recovery route is chemical transformation, the CO2 in this case being used as a raw material and a reagent. Numerous possibilities exist: organic synthesis, dry reforming, hydrogenation, thermochemical conversion, electrolysis, mineralisation, etc. This transformation route enables the manufacture of products and chemical compounds such as urea, salicylic acid (used in France in aspirin and dermatological products), cyclic carbonates (used in solvents, lithium-ion batteries, paints and coatings) and, before long, other products requiring pure CO2. Via electrochemistry, it enables the production of plastic polymers such as polycarbonate (used in spectacle lenses, CDs and DVDs, etc.)
Chemical transformation also offers the production of synthetic fuels, generally via conversion of CO2 into CO followed by recombination with hydrogen. In addition to ethanol initiatives, we should also mention the HyScale 100 project in Germany for methanol production, or the installation by Leroux & Lotz of a capture demonstrator at AscoMetal in Fos-sur-Mer (France) intended to produce e-methane. Other specialist players in the sector include Dioxycle, Twelve and Prometheus Fuels.
Meanwhile, chemical transformation is also useful in the production of construction materials. This is referred to as mineralisation or carbonation. By way of example, the US company Blue Planet Systems specialises in mineralisation in concrete. The British company O.C.O. Technology has developed a solution which provides accelerated formation of calcium carbonate from the reaction between wastes and CO2.
CO2 can alsobe recovered via biological pathways. It can then be used as nutrient for organisms which use photosynthesis to produce biomass, a source of many beneficial products, of which the most interesting example currently is algae. Algae cultivation is of particular interest for the agrifood and pharmaceutical industries (oils, proteins etc.), in water treatment (abatement of nitrogen and phosphorus) and in biofuels (or ‘algofuels’). So for example CarbonWorks (a recent joint venture between Fermentalg and Suez) is producing an algal bio-component that can be used as a fungicide to replace artificial pesticides in ademonstrator on a methanisation site in Gironde, SW France. The company plans a semi-industrial scale photobioreactor for 2023, having raised €11M in funding during 2022.
Looking beyond algae, also of note is the solution put forward by British company ,Deep Branch , which aims to replace soya-based animal feeds with proteins based on CO2 recycled via a fermentation process, or the American company, Kiverdi, which is developing bioreactors able to transform CO2 into nutrients that, mixed with others, produce a fishmeal.
The obstacles to overcome
The main obstacle to CO2 recovery is the energy intensity of the process. With this in mind, advanced conversion systems (electrolysis in particular) and thermochemical conversion powered by solar energy appear to be of most interest. A further question is that of transport. In fact the sector’s expansion will require – as does hydrogen – not only pipelines and terminals, but also suitable vessels and trucks.
The timespan over which the CO2 remains locked away is another significant factor. Recovery into construction materials offers to provide longer sequestration times than does transformation into chemical products (max. 10 years) or fuels (one year at most). Moreover, as part of its work for the “carbon capture, utilisation and storage” sector the CNRS is focusing its research on three pillars: activate and transform CO2 through less energy-consuming processes, respect the principles of green chemistry and integrate economic and life cycle analyses. In addition to the storage timespan, this last pillar puts the emphasis on the question of the additional CO2 emitted during the recovery process itself.
What about emissions reduction?
For the International Energy Agency (IEA), CO2 recovery is not necessarily synonymous with emissions reduction. A number of factors need to be taken into account: the source of the CO2 (biogenic, captured from the air or fossil fuels – the first two being of most interest); the product or service which the CO2-based product replaces but also, as seen above, the carbon intensity of the energy used for the conversion process and the CO2 sequestration time in the product. The size of the market for this particular utilisation comprises another important point to take into account.
In any event, all of these CO2 recovery processes form part of a global circular carbon economy approach and, as such, they must be encouraged.
*Source: Global Carbon Project. Of these 40.6 billion tonnes, 36.6 bn are of fossil fuel origin and 3.9 bn are linked to change of land use (including deforestation)