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 mitigatingCO(2) emissions. One of the potential CCS concepts is tocompressand store the captured CO2 into deep oceanic sedimentsas gas hydrates. However, seawater is highly saline [brine], whichmay impair the formation/dissociation kinetics and storage of CO2 hydrates. Therefore, it is essential to understand the liquidCO(2) [LCO2] hydrate formation and dissociationkinetics in static brine systems. In this experimental study, we haveexamined the formation/dissociation kinetics and morphology of high-pressureLCO(2) hydrates in brine using a static [unstirred] high-pressurecrystallizer at deep oceanic [1 km] thermodynamic conditions [10 MPa,1-2 degrees C]. The results are compared with [unstirred/stirred]freshwater systems with/without hydrate promoters. Three key stageshave 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 intothe brine, and most likely, the volume expansion during hydrate formationcauses the LCO2-hydrate-brine film to break. New hydratemorphological growth patterns have been identified. It was estimatedthat 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 dissociatefaster in brine [1.7 (+/- 0.14) h] compared to the freshwater system[5.7 (+/- 1.77) h]. Finally, the presence of the eco-friendly hydratepromoter 500 ppm l-tryptophan can delay the dissociationprocess.

Automated summary

Carbon capture and storage [CCS] is essential for reducing CO2 emissions, and one potential CCS concept is compressing and storing captured CO2 as gas hydrates in deep oceanic sediments. However, the high salinity of seawater may affect the formation and storage of CO2 hydrates. Therefore, it is crucial to understand the kinetics of liquid CO2 hydrate formation and dissociation in static brine systems.