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

Abstract

Carbon capture and storage [CCS] is crucial for mitigating CO 2 emissions. One of the potential CCS concepts is to compress and store the captured CO 2 into deep oceanic sediments as gas hydrates. However, seawater is highly saline [brine], which may impair the formation/dissociation kinetics and storage of CO 2 hydrates. Therefore, it is essential to understand the liquid CO 2 [LCO 2 ] 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 LCO 2 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 ], LCO 2 -hydrate-brine film formation [ stage 2 ], and LCO 2 -hydrate-brine film breakage [ stage 3 ]. In the absence of stirring, the formation of the LCO 2 -hydrate-brine film resists the mass transfer of LCO 2 into the brine, and most likely, the volume expansion during hydrate formation causes the LCO 2 -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]. LCO 2 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.