Molecular Dynamics simulation study of the performance of different inhibitors for methane hydrate growth

The methane hydrates can form blockages that occlude the flow in oil and gas pipelines increasing the risk of pipeline rupture with economic losses and can even cause accidents. One of the alternatives to avoid these problems is to inject some gas hydrate inhibitor into the flow, in this way the stability conditions of the hydrate are shifted to higher pressures and lower temperatures or the hydrate growth can be delayed for a longer time. In this work, the effect over the methane hydrate growth is studied for six different types of gas hydrate inhibitors using Molecular Dynamics simulations: Methanol, ethylene glycol, two aprotic ionic liquids EMIM-Cl and EMIM-NO3, and two protic ionic liquids EAF and TMACl. Traditionally, inhibitors such as methanol have been used, and aprotic ionic liquids have been studied more recently, but protic ionic liquids have received very little attention. These compounds are worth studying because they represent economic advantages in their synthesis and purification. For these reasons, this work aims to deepen the way in which the three types of gas hydrate inhibitors, conventional thermodynamic inhibitors, aprotic and protic ionic liquids act at the atomistic level. The results of the simulations were used to calculate changes in the number of hydrogen bonds between water molecules, structural order parameters F-3 and F-4, partial density profiles and radial distribution functions between water and gas hydrate inhibitors. The results indicate that TMACl was the best preventing the growth of the methane hydrate. This is due to a decrease of up to 5% of the hydrogen bonds between the water molecules, with respect to those that are formed in a system without inhibitor. In this case the inhibitor can form several hydrogen bonds with other water molecules, which causes a competition between the inhibitor and the water molecules of the hydrate for the free liquid water molecules. (C) 2021 Elsevier B.V. All rights reserved.