Increase in Subcooling Elevates the SDS Concentration Threshold for Significantly Promoting CH₄ and CO₂ Hydrate Formation

Enhancing the efficiency of CO2 hydrate formation is crucial for submarine CO2 sequestration via the solid hydrate method. Sodium dodecyl sulfate (SDS), a typical kinetic promoter for CH4 hydrate formation, has been investigated to be ineffective in promoting the formation of CO2 hydrate formation. However, the failure mechanism remains unclear. This study utilized a combination of optical microscopy and Raman spectroscopy to investigate the effects of SDS concentration (Csds) and hydrate formation subcooling (ΔTsubf) on hydrate film formation, through a comparative analysis of CO2 and CH4 hydrates. The results revealed that the relative Csds to ΔTsubf is the key factor determining the effectiveness of SDS. The Csds must exceed the corresponding critical concentration to obviously promote hydrate formation at different ΔTsubf. Based on these findings, we proposed the “chase mechanism”. Static CO2 hydrate formation kinetic experiments in SDS solution, based on the regulation of the two key factors, were further conducted and achieved a significant enhancement of the hydrate formation rate. Approximately 70% CO2 hydrate conversion was realized within 250 min, which is more than an order of magnitude faster than previously reported CO2 hydrate formation rates with SDS. The findings of this study are not only important for improving the efficiency of submarine CO2 hydrate sequestration but also provide methodological insights for identifying other potential hydrate formation kinetic promoters.