Ammonium hydroxide ILs as dual-functional gas hydrate inhibitors for binary mixed gas (carbon dioxide and methane) hydrates

In this study the dual-functionality of four ammonium based Ionic Liquids (AILs) having hydroxide anion namely: tetramethyl ammonium hydroxide (TMAOH), tetraethyl ammonium hydroxide (TEAOH), tetrapropyl ammonium hydroxide (TPrAOH) and, tetrabutyl ammonium hydroxide (TBAOH) is investigated on binary mixed gas hydrates (50 mol%-50 mol% CO₂-CH₄). For thermodynamic behaviour, the hydrate liquid vapour equilibrium (HLVE) data are generated in the presence of 10 wt% AILs solutions by the T-Cycle method at temperature and pressure conditions of 275.0–284.0 K and 2.0–6.50 MPa, respectively. THI results revealed that apart from TBAOH, all the considered AILs can shift HLVE curve towards higher pressure and lower temperature regions. Obtained results are further compared with commercial THI inhibitors. Average suppression temperature (Ŧ), Enthalpy of hydrate dissociation (∆H_diss) and Freezing point temperature (T_f) are also calculated for considered systems. The electrolyte based model is applied for validation of experimental HLVE data. Also, formation kinetics of studied AILs is reported for 1 wt% aqueous AILs solutions at 6.50 MPa with different experimental temperatures (274.0 K and 277.0 K). Induction time, initial formation rate, Relative Inhibition Power (RIP) and total gas uptake are the reported parameters for kinetic study. Furthermore, kinetic results are compared with commercial kinetic inhibitor namely: polyvinyl pyrrolidinium (PVP) at 274.0 K condition. Kinetic data suggested that all the studied AILs can perform as KHI inhibitors. Therefore, the considered AILs (except TBAOH) are able to perform as dual-functional inhibitors which highlight the use of AILs as a potential dual-functional gas hydrate inhibitors for sustainable flow in gas transmission pipelines.