New insights into the effect of polyvinylpyrrolidone (PVP) concentration on methane hydrate growth. 2. Liquid phase methane mole fraction

Kinetic hydrate inhibition studies generally characterize the effect of inhibitors on the crystal phase during formation and growth conditions. However, little work has been conducted to investigate the influence of the inhibitors on the gas hydrate former in kinetically inhibited systems. The current study examines the effect of polyvinylpyrrolidone (PVP) on methane mole fraction in the bulk liquid phase during growth. Hydrates were formed in an isothermal/isobaric semi-batch stirred crystallizer maintained at 275.1 K and 5645 kPa that contained aqueous solutions of 0-0.07 wt% PVP. Mole fraction measurements were taken from liquid samples extracted at 450 s and 900 s after the start of hydrate growth. Results indicated that while PVP had a negligible effect on methane solubility, the degree of supersaturation was significantly enhanced with inhibitor loading. The increase in supersaturation was attributed predominantly to a reduced surface area available for enclathration of methane into the hydrate lattice due to PVP binding. Correlation of mole fraction results to growth rate data through a kinetic model further pointed to a significant decrease in the total surface area available for reaction as a function of inhibitor loading.