Impacts of Stirring Rate on CO 2 -in-H 2 O Emulsion Synthesis and Stability for Enhanced CO 2 Hydrate Formation Kinetics

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With the global demand for carbon reduction, hydrate-based CO 2 sequestration evolves as a promising technology for offshore CO 2 storage. However, the slow kinetics of CO 2 hydrate formation, primarily due to the limited contact area and mass-transfer resistance between immiscible liquid CO 2 and the H 2 O phases under high pressures, remain a critical bottleneck for its practical application. To this end, we proposed a CO 2 -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.e., stirring rate, impacts the stability of the C/W emulsion and the subsequent CO 2 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 CO 2 gas uptake and rapid CO 2 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 CO 2 hydrate formation kinetics, and high CO 2 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 CO 2 hydrate formation kinetics promotion, which can be adopted in a series of CO 2 hydrate-based applications.

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