Gas hydrate nucleation in acoustically levitated water droplets

Abstract

We report subcooling-dependent measurements of hydrate formation on water droplets suspended via acoustic levitation in high-pressure natural gas. Ninety independent visual induction time measurements enabled the construction of induction time distributions with nucleation rates extracted at subcoolings of (12, 13.4 and 14.5) K. Using models from classical nucleation theory, kinetic and thermodynamic nucleation parameters were determined for freely suspended droplets and subsequently compared to those measured in more traditional stirred reactors. Scaling of the observed nucleation rates by each system's gas–water interfacial area led to improved consistency between the datasets. However, we show that while hydrate formation rates in systems with solid containing surfaces are determined by a small number of nucleation sites with low nucleation work, formation rates in levitated droplets are set by sites that have higher nucleation work but are more numerous. This leads to distinct subcooling-dependencies for nucleation rates in the two systems. These results provide insight both into hydrate promotion and avoidance strategies that are relevant to multiple applications.