Molecular dynamics simulations for selection of kinetic hydrate inhibitors

Natural gas hydrates are ice-like structures composed of water and gas molecules that have long been a problem in petroleum industry. Heavy cost of alcohol and glycol injection has spurred an interest in called 'kinetic inhibitors' able to slow down the hydrate formation rather than prevent it. Since it is not possible to compare directly the macroscopic effects of different inhibitors on the kinetics of hydrate formation in computer experiments, a scheme capable of culling the list of candidates for experimental testing was proposed earlier [B. Kvamme, G. Huseby, O.K. Førrisdahl, Molecular dynamics simulations of PVP kinetic inhibitor in liquid water and hydrate/liquid water systems, Mol. Phys. 90 (1997) 979-991]. Molecular dynamics simulations were implemented to test several kinetic inhibitors in a multiphase water-hydrate system with rigid hydrate interface. In addition, a long-scale run was implemented for a system where the hydrate was free to melt and reform. Our conclusion that PVCap will outperform PVP as a kinetic hydrate inhibitor is supported by experimental data. We demonstrate that numerical experiments can be a valuable tool for selecting kinetic inhibitors as well as provide insight into mechanisms of kinetic inhibition and hydrate melting and reformation.