Séminaire

Vendredi 11 Avril 2025 à 11h00.

Exchange dynamics in an aqueous foam charged in CO2

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In order to limit global warming, several IPCC scenarios are based on an intensive capture of CO₂ from the atmosphere. This objective is technically ambitious since it requires the development of processes to capture the diluted CO₂ from air (relative concentration of 0.04%), to separate it from other gases in the atmosphere and to concentrate it in order to limit the storage volumes.
In this context, using aqueous foams to bring CO₂ and the absorbing liquid solvent into contact offers several advantages: i) the foams have a large gas/liquid exchange surface, ii) they are fluid and can therefore be destroyed or regenerated on demand iii) their selectivity for the transfer of CO₂ compared to nitrogen or oxygen is high and little hindered by the surfactants present at the gas/liquid interfaces. However, the kinetics of gas transfer through the soap film can reveal surprising features, including reversible adsorption of a gas onto the self-assembled monolayer. I investigate the dynamics of CO₂ transfer in binary-gas foams, where bubbles contain a mixture of CO₂ and nitrogen — gases with different solubilities and affinities for the liquid phase.
In classical single-gas foam the structure evolves under the effect of gas flow induced by Laplace pressure differences, arising from heterogeneities in bubble size, which leads to the well-documented Ostwald ripening. However, in binary-gas foams, gas transfer is primarily driven by diffusion induced by partial pressure differences (or osmotic pressure).
Notably, under specific conditions, bubbles can shrink rather than grow. My results show that an effective gas diffusivity can be defined, influenced by initial bubble size, gas mixture composition and external atmosphere. By tuning these parameters, we can actively control the diffusivity of the different gases in the foam, offering new strategies for optimizing CO₂ capture in foam-based systems.

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