Understanding TEG and methanol in CO₂ transport
September 2026
CO₂ streams are never just CO₂.
Depending on how CO₂ is captured, treated and dehydrated, small amounts of other components can remain in the stream. Some of them may look insignificant in a specification but can become important once the CO₂ is compressed and transported.
In a recent collaboration, we report new measurements of the solubility of triethylene glycol (TEG) and methanol (MeOH) in CO₂ under conditions relevant to pipeline transport. Experimental data for these systems are still very limited, and published datasets for both MeOH and TEG do not always agree. In this study, we used high-precision measurements from a high-pressure saturation unit coupled with NMR spectroscopy.
The study also compared the measurements with thermodynamic models. The differences between experimental data and model predictions are a useful reminder that modelling remains essential, but still needs to be checked against real measurements.
Beyond the thermodynamics, these impurities also have practical implications for CO₂ transport. TEG is widely used to dehydrate natural gas, so applying similar technology to CO₂ may seem logical. But because of its low solubility in CO₂, TEG carry-over can contribute to the formation of a separate aqueous phase and increase corrosion risk. As a result, TEG is excluded or tightly limited in many CO₂ specifications. This has a practical consequence: CCS projects may need to consider different approaches to CO₂ dehydration rather than simply transferring established natural-gas practice.
Methanol raises a different issue. It can be useful operationally, for example to mitigate hydrate formation, but in the presence of other impurities such as NO₂ it may also participate in chemical reactions that form highly undesirable products, including methyl nitrite and nitric acid.
So should methanol also be excluded from CCS transport specifications?