Modulating Carbon Dioxide Hydrate With Ammonium and Phosphonium‐Based Deep Eutectic Solvent: A Molecular Dynamics Study of Cage‐Specific Dissociation Mechanism

The controlled release of CO₂ from structure I (sI) hydrates is essential for advancing carbon capture and storage (CCS) technologies. This study utilizes molecular dynamics (MD) simulations to investigate the pressure-dependent (1-80 bar) dissociation of CO₂ hydrates in two aqueous deep eutectic solvents (DESs) medium: tetrabutylammonium bromide/ethylene glycol (TBAB/EG, DES1) and methyl triphenyl phosphonium bromide/ethylene glycol (MTPB/EG, DES2), each in a 1:4 M ratio. The results demonstrate that both pressure and DES composition critically influence hydrate stability. DES1 promotes greater CO₂ release by reducing the CO₂ density from 640 kg/m³ within the sI hydrate to 206 kg/m³ at the sI hydrate-aqueous DES1 interface at 80 bar. DES1 shows more hydrogen bonding between CO₂ and aqueous water, while enhancing CO₂ mobility, outperforming DES2. The radial distribution function (RDF) analysis shows that CO₂ interacts more strongly with aqueous water in the presence of DES1, with a coordination number (CN) of approximately 27.02 at 1 bar, compared to DES2, which shows a maximum CN of about 26.37 at 1 bar. Higher CO₂ mobility in the aqueous DES1 phase from CO₂ hydrate is further supported by mean square displacement (MSD) compared to DES2. These findings establish a molecular-level framework for understanding how DES composition modulates hydrate dissociation, offering valuable insights for the rational design of DES-based media for targeted CO₂ sequestration.