Kinetic hydrate inhibitor performance and adsorption characteristics of poly(N-alkyl-N-vinyl acetamide)s: A first-principles study

Abstract

Kinetic hydrate inhibitors (KHIs) have been developed to prevent hydrate plugging of flow lines due to high efficiency and low dosage, but the intrinsic mechanism remains inconclusive and requires further verification. In this work, the inhibition performance of poly(N-alkyl-N-vinyl acetamide)s having varying alkyl side chain lengths has been investigated by the first-principles calculations and simulations. Further, the adsorption properties of these KHIs on various sites of the hydrate surface are considered. The results show that KHIs can adjust their positions and orientations to fit the empty cages, and that the adsorption strength is enhanced by increasing the alkyl side chain length, which is attributed to both hydrogen bonding and hydrophobic interactions. KHIs can drive CH4 away from the hydrae surface, but also can hold the lattice positions of water cages, which is responsible for reducing gas uptake and inhibiting hydrate growth. The molecular properties of KHIs indicate that the chemical reactivity increases with the increase of the alkyl side chain length, leading to the strong adsorption strength between KHIs and the hydrate surface, and thus improve the inhibition performance of KHIs. These results provide not only an important understanding of the KHI inhibition mechanism but also a basis for designing high efficient KHIs.