Clathrate nucleation and inhibition from a molecular perspective

Identifying the molecular processes that lead to clathrate-hydrate nucleation has been an active area of research for more than a decade. The question has a number of important ramifications, spanning applications in geology (formation and stability of natural methane-hydrate deposits), environmental science (CO2 sequestration), and industry (prevention of hydrate blockages). The drive to develop more active and robust hydrate inhibitors for the oil industry that work at very low dosages, in particular, has been slowed down because our understanding of the molecular mechanisms by which such inhibitors work is still largely conjectural. In this paper, we present results from the first direct molecular-dynamics simulations of the inhibition of nucleation in methane hydrate. Molecular-dynamics simulations have been used to simulate the behaviour of a thin film of water under a methane atmosphere with and without poly(vinylpyrrolidone) (PVP). Simulations in the absence of PVP show clear evidence of the nucleation and growth of methane hydrate; this behaviour is completely suppressed, however, when PVP is included in the simulation. We conclude that these simulations provide an excellent basis for understanding the way in which PVP inhibits hydrate nucleation.