Molecular Dynamics Simulations of Hydrophobic Nanoparticle Effects on Gas Hydrate Formation

Abstract

To investigate the effect of particle-based hydrate inhibitors on hydrate crystallization, molecular dynamics (MD) simulations were performed at the interface of hydrate-forming liquids where 2 nm sized silica nanoparticles are stabilized. The hydrophobic nanoparticles were prepared by functionalization of CH 3 groups on the amorphous SiO 2 surface, and the three-phase contact angle of the oil (CH 4 + decane), the aqueous phase (water + tetrahydrofuran (THF)), and the solid was 108.7°. Although the hydrates were not crystallized on the solid substrate, there was a trend that hydrate nucleation occurred on the side of the aqueous phase in the presence of nanoparticles. Through the four-body structural order parameter profiles, the formation of a low order parameter layer around the nanoparticles was observed, which originates from the reduced diffusivity by water binding. Adjacent to this layer, an elevation of the order parameter appeared in the same region where nucleation occurs because the less ordered layer acts as nucleation seeds. Indeed, a well of low free energy is formed in the presence of nanoparticles, in contrast to the nonnanoparticle system where no significant deviations were observed. Also, the driving force of hydrate nucleation is reduced with the increased nanoparticle injection. The nanoparticles prevented the diffusion of methane into the aqueous phase, resulting in a Vshape graph of induction time and delayed hydrate growth rate. These simulation results on the nanoparticle effect will provide a fundamental basis for improving the performance of particle-based inhibitors.

Experiment Investigation of SiO2 Containing Amino Groups as a Kinetic Promoter for CO2 Hydrates

“…RNS-A has relatively good thermal conductivity and can remove heat more efficiently and faster. , Second, RNS-A with smaller particles can provide a larger gas–liquid contact surface area . Third, SiO 2 can also be the seeds of heterogeneous hydrate nucleation, providing nucleation sites, increasing the probability of nucleation, reducing the driving force required for the reaction, and shortening the induction time. ,− In addition, the Brownian motion of RNS-A and the stirring of the magnetic stirrer intensify the collision between RNS-A and destroy the bound water molecules on the surface . Moreover, Bai et al .…”

“…Nevertheless, the formation of gas hydrates is an exothermic process that causes temperatures to rise, thus reducing the driving force for hydrate formation. RNS-A has relatively good thermal conductivity and larger contact surface area, which can remove heat more efficiently and faster. ,, In addition, RNS-A can act as seeds of heterogeneous hydrate nucleation, providing nucleation sites, increasing the probability of nucleation, and enhancing the driving force to promote hydrate formation. − Meanwhile, the Brownian motion of RNS-A can reduce the film resistance at the gas–liquid interface and enhance the mass transfer effect. , In addition, the Brownian motion of RNS-A and the stirring of the magnetic stirrer destroy the bound water molecules on the surface, which promotes the hydrate formation.…”

Research progress on the effects of nanoparticles on gas hydrate formation

“…This study not only verified the promoting effect of nanoparticles on the formation and decomposition of CO 2 hydrate, but also tried to reveal the influence mechanism of nanoparticles on the formation and decomposition of CO 2 hydrate from the physicochemical level. Min et al 82 from J. W. Lee team of Korea Institute of advanced science and technology used molecular dynamics simulation (MDS) studied the effect of hydrophobic nanoparticles on the formation of CH 4 –THF binary hydrate. It was pointed out that the hydrate cell formed on the inner wall of hydrate provided heterogeneous station sites conducive to hydrate formation.…”

Recent advances in density functional theory and molecular dynamics simulation of mechanical, interfacial, and thermal properties of natural gas hydrates in Canada

“…[30] Contrary to standard DFT, MD simulations can occur at reasonable temperatures, instead of 0 K. There has been remarkable success in studying gas hydrates with MD in the past, with systems ranging in size from hundreds to millions of atoms. [28,52,[54][55][56][57][58][59] MD applies classical mechanics to atomic and molecular structures. The forces acting on all the atoms are calculated, and Newton's equations are solved to calculate how the molecules move.…”