Homogenous nucleation rate of CO₂ hydrates using transition interface sampling.

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Carbon dioxide (CO2) and water form solid clathrate hydrates, with potential applications in CO2 sequestration.
• The precise mechanism of homogeneous nucleation, a rare event due to high free energy barriers, remains poorly understood.
• Brute force simulations are infeasible for studying hydrate nucleation under moderate conditions.

Purpose of the Study:

• To quantify the homogeneous nucleation rate of CO2 hydrate formation.
• To investigate the kinetics of clathrate formation using atomistic simulations.
• To compare simulation results with classical nucleation theory and experimental data.

Main Methods:

• Transition Interface Sampling (TIS) simulations were employed.
• Accurate atomistic force fields were utilized for CO2 hydrate formation.
• Simulations were conducted at 500 bars across three temperatures (260 K, 265 K, 273 K).

Main Results:

• Nucleation rates were computed for amorphous and sI crystalline phases at different temperatures.
• At 260 K, the amorphous phase nucleation rate was ~10^21 nuclei s^-1 cm^-3.
• At 265 K, the amorphous phase rate was ~10^12 nuclei s^-1 cm^-3, and at 273 K, the sI crystalline phase rate was ~10^1 nuclei s^-1 cm^-3.

Conclusions:

• The study provides quantitative nucleation rates for CO2 hydrate formation.
• Findings offer insights into the kinetics of this important clathrate system.
• Results will aid future investigations into hydrate formation mechanisms and CO2 sequestration strategies.