Low-pressure CO2 capture via semi-clathrate hydrates: Phase equilibria and structural analysis

초록

This study explores the thermodynamic and structural characteristics of semi-clathrate hydrates (TBAB & sdot;26.0 H2O + CO2, TBAC & sdot;30.0 H2O + CO2, and TBAF & sdot;29.7 H2O + CO2), which are emerging as promising low-energy media for CO2 capture. Three-phase equilibrium (semi-clathrate hydrate (H)-liquid (L)-vapor (V)) data were measured across 0.2-4.0 MPa, with particular emphasis on low-pressure conditions (0.2-1.0 MPa), where quantitative equilibrium data remain limited. The resulting phase equilibrium provides essential thermodynamic information for evaluating semi-clathrate hydrates under practical operating conditions. Structural analyses using powder Xray diffraction (PXRD) verified tetragonal crystalline frameworks, while Raman spectroscopy confirmed selective CO2 enclathration within dodecahedral (512) cages. Temperature-dependent dissociation experiments revealed that TBAB & sdot;26.0 H2O + CO2 and TBAC & sdot;30.0 H2O + CO2 hydrates completely decomposed near 293 K, whereas TBAF & sdot;29.7 H2O + CO2 hydrates retained crystallinity at this temperature and transitioned into a cubic phase before complete decomposition at 313 K. Hydrate formation kinetics and storage performance evaluated at 0.8 MPa showed that TBAC & sdot;30.0 H2O + CO2 hydrates achieved the highest CO2 storage capacity. Collectively, these results provide fundamental thermodynamic and structural insights into semi-clathrate hydrates under mild conditions and establish essential baseline data for the design of future low-pressure CO2 capture systems. By providing systematic equilibrium data together with detailed structural characterization and comparative CO2 storage performance evaluation, this study clarifies how distinct crystallographic features and thermal behaviors influence storage capacity, thereby strengthening the connection between fundamental hydrate thermodynamics and practical CO2 capture applications.

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