The present work investigates equilibrium conditions and dissociation enthalpies of semiclathrate hydrates formed from CO2 – tetra-n-butylammonium chloride (TBACl) – water, CO2 – tetra-n-butylammonium nitrate (TBANO3) – water and CO2 – tetra-n-butylphosphonium bromide (TBPB) – water mixtures. Differential scanning calorimetry (DSC) was used for the determination of hydrate-liquid-vapor (H-L-V) equilibrium conditions in the presence of TBACl, TBANO3 and TBPB solutions at ammonium salt mass fractions of 0.3618, 0.3941 and 0.3707, respectively, and at CO2 partial pressure ranging from 0.5 to 2.0 MPa. Results reveal that semiclathrate hydrates of TBACl, TBANO3 and TBPB are able to incorporate carbon dioxide in their structure and that the resulting mixed hydrates have significant lower formation pressures than pure CO2 hydrate. The dissociation enthalpies of semi-clathrate hydrates of TBACl, TBANO3 and TBPB with CO2 were determined by both DSC and Clausius-Clapeyron equation. The DSC experiments demonstrate that mixed hydrates of TBANO3, TBACl and TBPB with CO2 have higher melting enthalpies (J/Kg water) than single hydrates. From our measurements, it appears that mixed TBPB-CO2 hydrate has appropriate stability conditions (P, T) and latent heat content for secondary refrigeration applications. DSC measurements combined with Clausius-Clapeyron equation show that mixed TBPB-CO2 hydrate can store large amounts of CO2, and thus could be attractive for gas capture and storage applications.
Mots-clefs : Fluides de réfrigération