(174b) Magnetic Resonance Measurements of Hydrate Shell Growth in Oil

In crude oil systems, hydrate may nucleate and grow at the interface of emulsified water droplets. When the droplets are large, initial hydrate nucleation may extend through only a portion of the shell, maintaining a liquid water core that has been suggested to grow slowly over time. In this work, we present novel benchtop nuclear magnetic resonance (NMR) pulsed field gradient (PFG) and relaxation measurements to monitor the formation of a hydrate shell from large water particles dispersed in a continuous cyclopentane phase. These techniques allow us to monitor hydrate growth inside the opaque exterior shell, revealing novel information about the evolution of shell morphology over time. NMR relaxation measurements were primarily used to monitor the hydrate shell growth kinetics, while PFG NMR diffusion experiments were used to determine the nominal droplet size distribution of the unconverted water core. A comparison of the mean droplet sizes obtained directly via PFG NMR and independently deduced from relaxation measurements revealed that the assumption of a shell model for hydrate systems was correct, but only after approximately 24 hours of shell growth. Initially, the hydrate growth was observed to be limited by heat transport, resulting in a porous shell with a larger surface area than a sphere of equivalent volume. After 24 hours, continued hydrate growth became mass transfer-limited, and the shell became thicker, more spherical, and less porous.