Investigation into the Inhibition of Methane Hydrate Formation in the Presence of Hydroxy- and Esteryl-Terminated Poly(N-vinylcaprolactam)

Adding hydrate inhibitors is an important method to prevent gas hydrates from blocking oil and gas pipelines and ground equipment. In this work, on the basis of polyvinyl caprolactam (PVCap), an ester group and a hydroxyl group were introduced into the molecular chain end of PVCap to synthesize a blocked modified inhibitor, Es-PVCap-OH. Fourier transform infrared spectroscopy, H-1 NMR, and gel permeation chromatography methods were used to characterize PVCap and Es-PVCap-OH. The inhibition performance of Es-PVCap-OH for the formation of methane hydrate was studied and compared with that of the kinetic inhibitor PVCap. Powder X-ray diffraction, Raman spectroscopy, and cryogenic scanning electron microscopy (cryo-SEM) were used to characterize the microstructure of methane hydrate. The results showed that Es-PVCap-OH had better kinetic hydrate inhibitor performance and higher maximum subcooling than PVCap at the same concentration for methane gas hydrate formation. With 1 wt % Es-PVCap-OH solution, the induction time of hydrate formation increased by about 1400 min compared with that of the pure water system. Es-PVCap-OH selectively acts on specific hydrate crystal planes and affects the relative peak intensities of crystal planes. The addition of Es-PVCap-OH can substantially reduce the occupancy ratio of methane in the large cages of the hydrate lattice and change the morphology of the hydrate from submicron pores to a scaly cluster.

Automated summary

Adding hydrate inhibitors, such as Es-PVCap-OH, is an effective method to prevent gas hydrates from blocking pipelines and equipment. This study investigated the inhibitory performance of Es-PVCap-OH for methane hydrate formation and compared it with the kinetic inhibitor PVCap. The results showed that Es-PVCap-OH exhibited better inhibitory performance and changed the morphology of the hydrate structure.