Molecular dynamics simulations on formation of CO2 hydrate in the presence of metal particles

Abstract

Understanding and controlling the growth of CO2 hydrates is critical for a variety of industrial applications, such as sequestration of greenhouse gases. Due to the excellent physical and chemical properties, metal nanoclusters are widely used as additives in hydrate experiments. However, little is known about the molecular mechanism of this process. In this study, molecular dynamics (MD) simulation was performed at 260 K and 30 MPa by adding different types of metal particles (Cu, Fe and Ag) and different mass fractions (0.2 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt% and 1.3 wt%) to study the growth kinetics of the CO2 hydrate system containing pre-placed hydrate crystal cells. Simulation results showed that the presence of these metal particles has a mixed effect on the growth kinetics, and the extent of the effect seems to varies with different additives and also with the concentration of the metal particles used. It was observed that Cu particles had the most obvious promoting effect on hydrate growth. When the mass fraction of Cu particles was between 0.2 wt% and 1.0 wt%, the rate of hydrate formation increased, especially at the mass fraction of 1.0 wt%. The growth rate of CO2 hydrate was almost 50% higher than that of pure water system at this concentration. In addition, Fe particles had a medium effect on promoting CO2 hydrate growth. Ag particles had no obvious effect on CO2 hydrate growth. Results show that the addition of metal particles with high specific surface areas greatly increases the mass and heat transfer among the gas, liquid and hydrate phases, which is conducive to the growth of CO2 hydrate.