Multiscale analysis of the hydrate based carbon capture from gas mixtures containing carbon dioxide

To reveal the kinetic performance of gas molecules in hydrate growth, hydrate formation from pure CO₂, flue gas, and biogas was measured using in-situ Raman and macroscopic methods at 271.6 K. In the in-situ Raman measurements, Raman peaks of gases in the hydrate phase were characterised and normalised by taking the water bands from 2800 to 3800 cm^-1 as a reference, whose line shapes were not found to have a noticeable change in the conversion from Ih ice to sI hydrate. The hydrate growth was suggested to start with the formation of unsaturated hydrate nuclei followed by gas adsorption. In hydrate formed from all tested gases, CO₂ concentrations in hydrate nuclei were found to be 23-33% of the saturation state. In the flue gas system, the N₂ concentration reached a saturation state once hydrate nuclei formed. In the biogas system, competitive adsorption of CH₄ and CO₂ molecules was observed, while N₂ molecules hardly evolved in hydrate formation. Combined with micro- and macroscopic analysis, small molecules such as N₂ and CO₂ were suggested to be more active in the formation of hydrate nuclei, and the preferential adsorption of CO₂ molecules took place in the subsequent gas adsorption process.