As Europe accelerates its efforts to reach climate neutrality by 2050, the development of a secure carbon capture, utilisation and storage (CCUS) infrastructure is becoming increasingly urgent. CCUS is not only vital for decarbonising hard-to-abate industrial sectors, but also for enabling negative CO₂ emissions. However, the deployment of CCUS at scale faces significant challenges — particularly in the area of CO₂ transport and the lack of common specifications for CO₂ purity.

CO₂ captured from industrial sources is rarely pure. Unlike naturally occurring CO₂ used in North American pipelines, anthropogenic CO₂ contains a variety of impurities, including sulphur oxides (SOₓ), nitrogen oxides (NOₓ), oxygen (O₂), and hydrogen sulphide (H₂S). These compounds can interact with pipeline materials, causing corrosion, altering phase behaviour, and forming solids that block valves and reduce flow. The presence of these impurities also raises health and safety concerns in the event of accidental release.

Current practices and the need for standardisation
Transporting CO₂ over long distances – often hundreds of kilometres – via pipelines, ships, trucks, or rail requires a deep understanding of its thermo-chemical behaviour. Impurities can exacerbate two-phase flow conditions, complicate pressure and temperature control, and increase the risk of hydrate formation. These phenomena are not only operationally challenging but also poorly understood, due to limited experimental data and modelling capabilities.
   

European projects such as Aramis, Northern Lights, and Porthos have developed internal guidelines for CO₂ purity, often setting impurity thresholds at extremely low levels – sometimes stricter than food-grade standards. For example, some specifications cap certain impurities at just a few parts per million (ppm), reflecting the high safety and integrity requirements of shared infrastructure.

However, these practices are not harmonised across the EU. There is currently no common European standard for CO₂ composition, and existing specifications are often project-specific and conservative due to uncertainty.

The German DVGW draft standard C260 represents one of the most advanced efforts to define basic specifications for pipeline transport. However, the work was put on hold because no sufficiently reliable CO₂ specification could be found in laboratory tests.

Meanwhile, the European Committee for Standardisation (CEN), through Technical Committee TC 474, is working towards a unified CO₂ transport standard that reflects the latest scientific findings. In May 2025, CEN/TC 474 published an urgent call for submissions of corrosion test data from industrial projects, which are normally confidential. Without contributions from this area, the European standardisation process could also come to a standstill.

As there are currently significant gaps in our understanding of the interactions between impurities, long-term material integrity and the behaviour of CO₂ mixtures under different transport conditions, further research in this area is imperative. Due to the existing time pressure, the best possible way to proceed is currently being discussed intensively.
  

Scientific and technical imperatives
To support the development of reliable CO₂ specifications, increased investment in laboratory testing, large-scale experimental validation, and international collaboration is needed. Advanced modelling tools have to be developed to simulate the behaviour of CO₂ mixtures under real-world conditions, including pressure fluctuations, temperature gradients, and multimodal transport transitions.

Moreover, the repurposing of existing natural gas pipelines for CO₂ transport presents additional challenges. Materials must be tested for compatibility with impure CO₂, and safe impurity limits must be established to prevent corrosion and ensure long-term integrity.

Toward a common European standard
The establishment of a common European CO₂ specification is essential for enabling interoperable infrastructure, reducing costs through standardised purification technologies, and ensuring the safety of transport and storage operations. However, the timing of standardisation is critical. Prematurely setting overly strict specifications could hinder innovation and raise barriers for new projects. Instead, a phased approach is recommended – starting with conservative, project-specific limits and gradually refining standards based on operational experience and scientific advancements.

In addition to purity specifications, standardisation in related areas, including health and safety protocols, MRV (Monitoring, Reporting and Verification), CO₂ origin tracking, third-party access, liability frameworks, and taxonomy is needed. These elements are vital for building a transparent, accountable, and scalable CCUS system.