Effects of kinetic inhibitors on the formation and growth of hydrate crystals at a liquid-liquid interface

The paper reports visual observations of the formation and growth of clathrate hydrate crystals at the interface between HCFC-141b (CH3CCl2F) and water to which a kinetic inhibitor, poly(N-vinylpyrrolidone) (PVP) or poly(N-vinylcaprolactam) (PVCap), was applied at 0.2wt% at most. The crystalline morphology of the hydrate at the interface was found to be substantially altered by the addition of either inhibitor. PVP causes a greater change in morphology than PVCap does, while PVCap shows a stronger inhibition effect on the hydrate growth at the interface. Despite its effect of reducing the rate of growth of hydrate crystals along the interface, PVP promotes the growth of hydrate crystals from the already hydrate-covered interface into the aqueous phase whether or not the phase is saturated by the hydrate former, HCFC-141b, in advance. The critical condition for complete inhibition has been determined for each inhibitor. (C) 2002 Elsevier Science B.V. All rights reserved.