Introducing sodium lignosulfonate as an effective promoter for CO2 sequestration as hydrates targeting gaseous and liquid CO2

Hydrate-based CO2 sequestration (HBCS) emerges as a promising solution to sequestrate CO2 as solid hydrates for the benefit of reducing CO2 concentration in the atmosphere. The natural conditions of high-pressure and lowtemperature in marine seabed provide an ideal reservoir for CO2 hydrate, enabling long -term sequestration. A significant challenge in the application of HBCS is the identification of an environmental-friendly promoter to enhance or tune CO2 hydrate kinetics, which is intrinsically sluggish. In addition, the promoter identified should be effective in all CO2 sequestration conditions, covering CO2 injection as gas or liquid. In this study, we introduced sodium lignosulfonate (SL), a by -product from the papermaking industry, as an eco-friendly kinetic promoter for CO2 hydrate formation. The impact of SL (0-3.0 wt.%) on the kinetics of CO2 hydrate formation from gaseous and liquid CO2 was systematically investigated. CO2 hydrate morphology images were acquired for both gaseous and liquid CO2 in the presence of SL for the explanation of the observed promotion effect. The promotion effect of SL on CO2 hydrate formation is optimal at 1.0 wt.% with induction time reduced to 5.3 min and 21.1 min for gaseous and liquid CO2, respectively. Moreover, CO2 storage capacity increases by around two times at 1.0 wt.% SL, reaching 85.1 v/v and 57.1 v/v for gaseous and liquid CO2, respectively. The applicability of SL as an effective kinetic promoter for both gaseous and liquid CO2 was first demonstrated. A mechanism explaining how SL promotes CO2 hydrate formation was formulated with additional nucleation sites by SL micelles and the extended contact surface offered by generated gas bubbles or liquid droplets with SL. The study demonstrates that SL as an effective promoter for CO2 hydrate kinetics is possible for adoption in large-scale HBCS projects both nearshore and offshore.