Molecular Dynamics Simulation of CH4 Hydrate Decomposition in the Presence of Poly(2-ethyl-2-oxazoline)

Abstract

Molecular dynamics simulations were carried out to study the decomposition of CH4 hydrate in the presence of poly(2-ethyl-2-oxazoline) (PEtO) at different concentrations, including 1.25% , 2.50%, and 6.06% (w, mass fraction). The simulation system was composed of a CH4 hydrate crystal and PEtO, which contained a 2×2×2 supercell of CH4 hydrate crystal and PEtO polymer. System configurations showed that hydrogen bonding networks between water molecules making up the main framework of the hydrate cages were distorted in the presence of the PEtO polymer. Final configurations in all of the systems were completely collapsed. Radial distribution functions of the oxygen atoms, mean square displacements, and diffusion coefficients of water molecules were applied to compare the effect of different PEtO concentrations on the CH4 hydrate. Within a certain concentration range, higher concentrations led to a better inhibition effect. It was confirmed that PEtO is a type of prospective low dosage inhibitor with biodegradability. The decomposition mechanism involves the absorption of the PEtO polymer onto the surface of the hydrate crystal, with its active functional group (N―C=O) forming hydrogen bonds with water molecules in the hydrate and decomposing the hydrate surface. PEtO continued to decompose the surface layer of hydrate, resulting ultimately in the collapse of the hydrate cages.