A molecular dynamic study of water/methane/propane

Abstract

We present a molecular dynamic simulation for water/methane/propane. The simulation is performed in a constant NPT ensemble at a temperature of 240 K and a pressure of 300 bar. The simulation is analysed to calculate the propensity for hydrogen bond formation, potential energy, number density profile and radial distribution function. Compared with the binary system (water/methane), relatively slight changes in hydrogen bond number and potential energy for the ternary system (water/methane/propane) indicate that the presence of propane retards the rate of hydrate growth. It is interesting to observe that propane, which is also of hydrophobic nature as methane, does not promote the formation of hydrate, but is rather driven out of the middle aqueous region. No hydrate formation was observed even after all of the propane had been driven out of the water film. We suggest that the size of water clusters and hydrogen bond network is likely to be disrupted by propane molecules, hindering the growth of the nuclei to the critical size required for sustained growth. The presence of the propane might also affect the net flux of methane into the aqueous phase, which is critical for hydrate formation.