Dependence\nof Gas Hydrate Formation Kinetics on System\nSize from Lag Time Experiments in a Stirred Pipe

High-pressure, stirred, automated lag time apparatus\n(HPS-ALTA)\nwith a vertical cylindrical geometry and a 10.8 mL volume has been\nused previously to characterize gas hydrate nucleation rates. However,\nthe relevant scale parameter that determines how such nucleation rates\nchange with system size remains uncertain. Herein, we present a new\nhigh-pressure stirred ALTA system with a horizontal, pipe-like geometry:\nPipe-ALTA. Beyond enabling measurement of hydrate formation probability\nunder stirred conditions in significantly larger fluid volumes (up\nto 300 mL), the pipe-like geometry also allows for system dimensions\nsuch as the gas–water interfacial area, α, to be modified\nby changing the water loading. In this study, we use Pipe-ALTA to\nmeasure induction times for gas hydrate formed from water and a synthetic\nnatural gas mixture. Nucleation rates in the Pipe-ALTA are highest\nwhen the gas–water interface is large: up to an order of magnitude\nhigher than those measured in the smaller HPS-ALTA (at comparable\nsubcooling). We demonstrate that the nucleation rates from the three\nsystem geometries (Pipe-ALTA at two liquid loadings plus HPS-ALTA)\ncan be reconciled if they are scaled by the gas–water interfacial\narea. In contrast, scaling by the three-phase contact line produces\nless consistent results, suggesting that the gas–water interfacial\narea is the most relevant scale parameter.