Thermodynamic effect of ammonium based ionic liquids on CO₂ hydrates phase boundary

In this experimental study, the phase boundary behavior of CO₂ hydrate is reported in the presence of 1, 5, and 10 wt% of three aqueous ammonium based ionic liquids (AILs) solutions. The T-cycle technique is used to measure the hydrate equilibrium conditions of AILs + CO₂ + H₂O hydrate systems within the ranges of 274–283 K and 1.80–4.20 MPa. All studied AILs inhibited CO₂ hydrate with the inhibition effect increasing with AILs concentration. The 10 wt%, TEAOH showed the highest inhibition effect with an average suppression temperature (∆ Ŧ) of 1.7 K, followed by TMACl (∆ Ŧ = 1.6 K) and then TPrAOH (∆ Ŧ = 1.2 K). Furthermore, COSMO-RS analysis is performed to understand the molecular level inhibition mechanism of AILs. In addition, the enthalpies of hydrate dissociation for all studied systems are also determined. The calculated hydrate dissociation enthalpies revealed that all the studied AILs show insignificant participation in CO₂ hydrate cage formation at all concentrations, hence, do not form semi-clathrate hydrates.