Impacts of Stirring Rate on CO₂‑in‑H₂O Emulsion Synthesis and Stability for Enhanced CO₂ Hydrate Formation Kinetics

With the global demand for carbon reduction, hydrate-based CO₂ sequestration evolves as a promising technology for offshore CO₂ storage. However, the slow kinetics of CO₂ hydrate formation, primarily due to the limited contact area and mass-transfer resistance between immiscible liquid CO₂ and the H₂O phases under high pressures, remain a critical bottleneck for its practical application. To this end, we proposed a CO₂-in-water (C/W) emulsion system by employing a nonionic surfactant, alkyl polyglucoside (APG), using simple high-speed stirring. We systematically examined how the degree of mixing, <i>i.e.</i>, stirring rate, impacts the stability of the C/W emulsion and the subsequent CO₂ hydrate formation kinetics. Using a full-visual reactor coupled with an in-house developed phase identification algorithm, C/W emulsification and demulsification kinetics were unveiled. C/W emulsion stability under various high stirring rates and APG concentrations was examined. We further demonstrate the superior CO₂ gas uptake and rapid CO₂ hydrate formation kinetics realized by the synthesized stable C/W emulsion. Our results suggest that increasing the stirring rate substantially speeds up the C/W emulsification synthesis process, achieving only 9 s at an optimal stirring rate of 1600 rpm and 3.00 wt% APG. The stability of C/W emulsion is further enhanced under high shearing rate, with complete demulsification time reaching 5 h. Furthermore, increasing the stirring rate from 800 to 1600 rpm not only improves the C/W emulsion stability but also results in shortened induction time, high CO₂ hydrate formation kinetics, and high CO₂ final uptake (maximum gas uptake 167.7 v/v with a water conversion of 84.5%). The experimental results provide direct evidence on how the stirring rate affects C/W emulsion preparation and stability. The findings also shed light on a promising emulsion-based method for effective CO₂ hydrate formation kinetics promotion, which can be adopted in a series of CO₂ hydrate-based applications.