Evaluation of hydrophilic and hydrophobic ionic liquids as dual-functional CH4 hydrate inhibitors: A combined experimental and simulation study

Abstract

Ionic liquids (ILs) have gained significant attention as dual-functional hydrate inhibitors, serving as thermodynamic and kinetic hydrate inhibitors. This study aimed to investigate a crucial factor determining the inhibition performance of ILs for CH4 hydrate, focusing primarily on their hydrophilicity or hydrophobicity, through a combination of experimental techniques and molecular dynamics simulations. The experimental results demonstrated that the thermodynamic and kinetic inhibitions of ILs for CH4 hydrate were influenced by their hydrophilicity or hydrophobicity, with more hydrophilic ILs exhibiting superior hydrate inhibition. Notably, hydrophobic ILs acted as kinetic hydrate inhibitors but lacked thermodynamic hydrate inhibition properties. Simulation results revealed that the thermodynamic inhibition of ILs originated from their interaction with water, which was stronger for more hydrophilic ILs, while IL adsorption on the growing hydrate surface served as a major mechanism for their kinetic hydrate inhibition. Free energy calculations confirmed the thermodynamic feasibility of IL adsorption on CH4 hydrate. Moreover, more hydrophilic ILs were found to be more likely to be adsorbed onto the hydrate surface due to their stronger binding affinity. Therefore, these findings contribute to a better understanding of the inhibition mechanism of ILs as dual-functional hydrate inhibitors and have implications for the development of new hydrate inhibitors.