Performance Ranking of 30 Clathrate Hydrate Crystal Growth Inhibitors Using the Unidirectional Growth Method

Numerous research groups have reported on their performance since the first-generation Kinetic hydrate inhibitors (KHIs) were discovered over 30 years ago. However, experimental setup and performance metrics variations have made direct comparisons challenging. As a result, researchers should exercise caution when comparing and interpreting KHI performance data across different studies. Our group proposed a simple and consistent method for evaluating hydrate crystal growth inhibitor (HCGI) performance to address this. This approach uses a unidirectional crystal growth apparatus with a stoichiometric tetrahydrofuran (THF)-water solution containing various HCGIs. In this study, we evaluated 30 different HCGIs using this method and established a performance ranking to serve as a unified index. All tests were conducted at a fixed HCGI concentration of 0.5 wt % and crystal growth velocities (V) of 1, 5, and 10 μm s^–1. Among the compounds tested, 1,6-bis-tributylaminohexane bis-oxide (1,6-TriBAHO) demonstrated the highest inhibitory performance across all velocities, better than any polymer tested. This high performance may come from the fact that the 1,6 spacing between its amine oxide groups closely matches the center-to-center distance between adjacent open L cages in structure II hydrate. Interestingly, 1,6-TriBAHO is an excellent THF hydrate crystal growth inhibitor but is less effective for gas hydrate. A strategy to apply this powerful effect to gas hydrates was discussed. Other top-performing HCGIs included a series of poly(vinylcaprolactam) (PVCap) compounds. These results were interpreted in the light of a promising hypothesis on the HCGI inhibition mechanism, supported by previous molecular dynamics (MD) studies.