The delay of gas hydrate formation by kinetic inhibitors

The formation of gas hydrates is crucial to many technological applications including energy production, energy storage, desalination, and CO₂ capture. Kinetic hydrate inhibitor (KHI) chemicals have been used industrially for over 25 years to suppress hydrate formation in key industrial applications. However the mechanisms by which they operate, and specifically whether they delay nucleation or just retard growth, remain open questions. Here induction time probability distributions for methane hydrates were measured at several constant subcoolings as a function of KHI concentration. This allowed the hydrate nucleation and growth rates at each condition to be separately quantified through the observed induction times and initial gas consumption rates, respectively. Adding a KHI produces a Gamma-distribution of induction times, characterized by two parameters: nucleation rate and the average number of events associated with detection. This is qualitatively different to the exponential distributions of induction time probabilities observed in systems without any KHI. These data reveal how KHIs both increase the nucleation work required to form a critical nuclei and increase the effective number of sites where nucleation could occur. By showing unambiguously how KHIs delay hydrate nucleation at low subcoolings, this work opens systematic pathways for developing improved chemicals for either hydrate inhibition or promotion. The approach to inhibitor testing demonstrated here may also help natural gas producers assess the costs and benefits of competing designs for hydrate management.