Whether smaller guest droplets facilitate hydrate conversion: Effects of nanodroplet size and droplet interactions from molecules perspective

Abstract

To overcome the self-limiting of hydrate formation, dispersing the guest phase into smaller droplets to create more guest-water interfaces provides an effective strategy for enhancing hydrate conversion. However, dispersing the guest phase into a larger number of smaller droplets requires additional energy, and whether it always enhances hydrate conversion remains unclear. In this work, the hydrate conversion of guest nanodroplets is investigated using molecular dynamics simulations. When the guest phase is dispersed into smaller droplets, moderate dispersion enhances hydrate conversion, whereas excess dispersion reduces the conversion ratio. This non-monotonic change of conversion ratio can be attributed to the coupled effects of droplet size and droplet density. For guest droplets with different sizes, smaller nanodroplets achieve higher conversion ratios owing to their larger surface-to-volume ratios. Accordingly, the conversion ratio decreases from approximately 45% for a droplet with a radius of 4.1 nm to 30% for a droplet with a radius of 9.2 nm in this work. As droplet density increases, the conversion ratio reaches a maximum at a moderate density. The initial enhancement results from hydrate bridging between neighboring droplets, whereas excessive density restricts the available growth space and suppresses individual droplet conversion. Thus, hydrate conversion during dispersion is governed by the coupled effects of droplet size and droplet interactions, indicating that partitioning the guest phase into an excessive number of small droplets may not always improve hydrate conversion.