Evaluation of Kinetic Inhibition of Methane Hydrate Formation by a Copolymer of N-Vinylcaprolactam with 1-Vinylimidazole

This study investigated methane hydrate inhibition by a new polyvinyl lactam-based kinetic hydrate inhibitor (KHI) by determining the maximum subcooling temperature, induction time, and growth rate using a high-pressure sapphire reactor. The studied KHI, namely, the random copolymer of N-vinylcaprolactam and 1-vinylimidazole (PVCap-co-VIM), was synthesized by free radical solution polymerization with the objective of producing copolymers with higher cloud points than the poly(N-vinylcaprolactam) (PVCap) homopolymer. These data were compared with those of laboratory-made PVCap and commercial poly(N-vinylpyrrolidone) (PVPK90) under various cooling rates (1.0, 2.0, and 5.0 K/h) and mass concentrations (0.5, 1.0, and 2.0 wt %). The experimental results showed that the cooling rate had little effect on the maximum subcooling temperature of the KHIs. PVCap-co-VIM was capable of delaying the nucleation of hydrate crystals for a longer time than PVPK90 and successfully suppressed hydrate growth in the early stage of hydrate formation. PVCap performed better than PVCap-co-VIM under the same conditions, but PVCap-co-VIM exhibited a significantly higher cloud point temperature (T-CI > 70 degrees C) than PVCap (T-CI = 37.9 degrees C), which was beneficial for field applications. Furthermore, the measured powder X-ray diffraction and Raman spectral data showed that the formed hydrate structures were the same (structure I) for all the studied KHI-containing systems, despite some differences in the characteristic peak intensities as a result of different inhibitory activities. Cryo-scanning electron microscopy images illustrated that the morphology of the formed CH4 hydrate crystals varied significantly by KHIs, which could be helpful for safe pipeline fluid transportation