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

Abstract

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 (C_sds) and hydrate formation subcooling (ΔT_subf) on hydrate film formation, through a comparative analysis of CO₂ and CH₄ hydrates. The results revealed that the relative C_sds to ΔT_subf is the key factor determining the effectiveness of SDS. The C_sds must exceed the corresponding critical concentration to obviously promote hydrate formation at different ΔT_subf. 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.