Investigating High-Pressure Liquid CO2 Hydrate Formation, Dissociation Kinetics, and Morphology in Brine and Freshwater Static Systems

Carbon capture and storage [CCS] is crucial for mitigating CO2 emissions. One of the potential CCS concepts is to compress and store the captured CO2 into deep oceanic sediments as gas hydrates. However, seawater is highly saline [brine], which may impair the formation/dissociation kinetics and storage of CO2 hydrates. Therefore, it is essential to understand the liquid CO2 [LCO2] hydrate formation and dissociation kinetics in static brine systems. In this experimental study, we have examined the formation/dissociation kinetics and morphology of high-pressure LCO2 hydrates in brine using a static [unstirred] high-pressure crystallizer at deep oceanic [1 km] thermodynamic conditions [10 MPa, 1–2 °C]. The results are compared with [unstirred/stirred] freshwater systems with/without hydrate promoters. Three key stages have been identified in the experiments: nucleation [stage 1], LCO2-hydrate-brine film formation [stage 2], and LCO2-hydrate-brine film breakage [stage 3]. In the absence of stirring, the formation of the LCO2-hydrate-brine film resists the mass transfer of LCO2 into the brine, and most likely, the volume expansion during hydrate formation causes the LCO2-hydrate-brine film to break. New hydrate morphological growth patterns have been identified. It was estimated that the hydrate conversion in the freshwater system was higher [27.5% (±3.04%) in 21.1 (±1.26) h] compared to the brine system [25.0% in 24.2 (±0.58) h]. LCO2 hydrates dissociate faster in brine [1.7 (±0.14) h] compared to the freshwater system [5.7 (±1.77) h]. Finally, the presence of the eco-friendly hydrate promoter 500 ppm l-tryptophan can delay the dissociation process.