Making use of CO2: a strategy for extracting economic value from CO2 while contributing to regional development

Suren Erkman, December 2023

The traditional climate strategy of mitigation, which naturally remains the priority, seeks to reduce greenhouse gas emissions at source.

However, it is clear that this strategy alone is not producing the desired results.

That’s why another approach has been developing rapidly in recent years: capturing CO2 from concentrated sources (cement works, steelworks, fertiliser plants, incinerators, etc.) or diluted sources, by capturing it directly in the air (Direct Atmospheric Capture, DAC). It can then be stored or recovered. It is this second option, which is of particular interest to local and regional authorities, that is presented here, along with the three methods of recovery: the direct use of CO2, its chemical transformation and its biological transformation. All three are part of the vast movement towards industrial and territorial ecology, which aims to take advantage of the complementarities between activities in the same area, just as nature itself does in ecosystems, with the waste from one being the raw material for the other.

Once the CO2 has been captured (and sometimes purified), there are two main options:

a) CO2 storage (or sequestration), abbreviated to CCS (Carbon Capture and Storage).

The captured CO2 is transported and then stored in deep geological structures. In addition to the technical difficulties and the risk of leakage, storage is characterised by its high cost.
b) Carbon Capture and Utilization (CCU).

Unlike CCS, CCU treats CO2 as a raw material and therefore gives it an economic value. CO2 can therefore be a source of revenue for companies or public bodies.

The possibilities for using CO2 are many and varied, and fall into three main categories:

1) The physical route, without transformation: CO2 is used as is as a fire-fighting agent, a cleaning agent (supercritical CO2), a fertiliser for greenhouse crops, or even as a heating or cooling agent in district heating and/or cooling networks (CO2-based networks offer certain technical and economic advantages over traditional networks using water or steam).
2) The chemical route, undoubtedly the most promising, which involves transforming the CO2 into various products: production of polymers, high added-value molecules (such as succinic acid), synthetic fuels (methane or methanol, in particular).

In particular, large quantities of CO2 can be recovered using two approaches:

Mineralisation: CO2 can react with different types of minerals (natural or industrial residues) to produce building materials through carbonation.
Chemical storage of surplus renewable electricity from intermittent sources (solar, wind). The excess electricity is used to electrolyse water, then the hydrogen obtained reacts with CO2 to produce methane (for example).

This process (known generically as Power to gas) naturally has an energy cost: but it is preferable to accept an energy penalty rather than having to offload all the surplus renewable electricity.

3) Biological conversion: in this case, the CO2 is captured by living organisms (photosynthesis): microalgae, bacteria, plants, etc. Various substances can then be extracted from the CO2. Various substances can then be extracted and used as they are or transformed to produce specific products (biofuels, polymers, etc.).

Energy issues :

Capturing and, above all, converting CO2 requires energy, particularly heat. However, certain chemical reactions such as the conversion of CO2 into methane (methanation) or the carbonation of mineral raw materials release heat (exothermic reactions).

For the transformation stages that require heat (endothermic reactions), the general principle is that of « territorial opportunism »: in a given area, there are always numerous sources of waste heat (incinerators, cement works, various industrial installations, etc.) available, often in large quantities. This considerably reduces the net energy input for capture and transformation operations.

Research into new catalysts that reduce the energy required for CO2 conversion reactions is also making rapid progress.

Territorial issues :

In a given area, there are three factors in favour of an approach such as CCU:

the presence of numerous sources of waste heat (sources that are still largely underused) ;
the presence of numerous sources of concentrated CO2 emissions (currently untapped);
the presence of numerous potential users of CO2 or by-products.

The combination of these three factors epitomises the industrial ecology approach: optimising flows and stocks of resources through synergies (or symbiosis) between existing (or even new) activities, taking advantage of resources that are currently little or poorly used.

In this context,the CO2 utilisation strategy makes it possible to set in motion development dynamics on a regional scale, combining socio-economic development (local production of value) and contribution to climate policies.