The influence of the kinetic inhibitor poly(N-vinylpyrrolidone) or PVP on hydrate methane/propane hydrate formation was studied in pre-saturated liquid water with and without the presence of heptane under different undercooling conditions. It was found that when the inhibitor concentration was 0.1 wt%, hydrate formation started as a film at the gas/water interface similar to the crystal behavior without inhibitor. When the inhibitor concentration was 0.5 wt% hydrate formation started at the wall above the gas/water interface and the hydrate film at the gas/water interface was observed as well. However, for inhibitor concentration 1.0 wt%, the hydrate started forming from water droplets attached to the wall above the gas/liquid interface and grew catastrophically.
When the inhibitor concentration was 0.1 wt% and undercooling was 13.7 or 8.1 K whiskery or fiber-type hydrate crystals, respectively, were seen within the liquid pool. This morphology was not observed in the absence of PVP. When inhibitor concentration was 0.5 or 1.0 wt% or undercooling was 3.2 K, there was no crystal growth within the liquid pool. Floating crystals were also observed, but were needle-type and thus different from the equiaxed floating crystals found in the system without the inhibitor.
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