Molecular
Dynamics Study on the Equilibrium and Kinetic
Properties of Tetrahydrofuran Clathrate Hydrates
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Abstract
Tetrahydrofuran (THF) is an effective
promoter of methane hydrates,
and itself with water can form clathrate hydrates even without the
presence of methane gas. In this work, the stability limit and kinetic
properties of THF hydrates were simulated using molecular dynamics
(MD) simulations. The change in dissociation temperature of THF hydrates
with pressure and concentration of THF in the aqueous phase were well
reproduced with MD simulations. The rate of growth of THF hydrates
is found to exhibit a maximum value when the liquid-phase THF concentration
is about 0.3β0.8 times (depending on temperature) of the THF
concentration in the hydrate phase. The existence of some optimal
growth concentration explains the preferred lateral growth in experiments.
The maximum growth rate is a result of two competing effects: the
adsorption of THF molecules to the growing interface, which is the
limiting step at low THF concentrations, and the desorption/rearrangement
of THF molecules at the interface, limiting step at high THF concentrations.
The large cages of structure II (sII) hydrate are fully occupied by
THF molecules, regardless of the THF concentration in the aqueous
phase, implying a strong stabilization effect of THF molecules to
the cage structures of sII hydrates