Insights into behaviors of guest and host molecules in methane hydrate formation process in the presence of kinetic inhibitors via in-situ micro-Raman spectroscopy

Abstract

In-situ microscopic observation on methane hydrate formation in the presence of kinetic hydrate inhibitor, poly (vinyl caprolactam) (PVCap) or poly (N-isopropyl acrylamide) (PNIPAM), is conducted with a confocal Raman imaging microscope, and the behaviors of CH4 molecules and water molecules in hydrate formation process are studied to understand the inhibition mechanism. It is found that both PVCap and PNIPAM have influences on hydrate formation, but their interactions with host and guest molecules are different. PVCap with cyclic pendant groups works better on preventing hydrate formation from the gas–liquid interface into the bulk solution, while PNIPAM with acyclic pendant groups is more effectively on inhibiting hydrate growth to well-ordered clathrate structures. Those are caused by the difference in the prominent inhibition mechanism of the two types of kinetic hydrate inhibitors, lactam-based PVCap mainly limiting the diffusion of CH4 molecules from the gaseous phase to the liquid phase, while non-lactam PNIPAM undermining hydrate growth by retarding the rearrangement of water molecules to form clathrate structures.