Diffusion coefficients in CO2/n-alkane binary liquid mixtures by molecular simulation

Area of Science:

• Thermodynamics and physical chemistry
• Computational fluid dynamics
• Chemical engineering

Background:

• Accurate diffusion coefficients are crucial for modeling processes in oil reservoirs.
• Experimental determination of Fick diffusivities in CO2/n-alkane mixtures is complex and expensive.

Purpose of the Study:

• To determine Fick diffusion coefficients in CO2/n-alkane binary mixtures computationally.
• To validate a simulation-based approach for predicting diffusion in high-pressure systems.

Main Methods:

• Calculated Maxwell-Stefan diffusivity via molecular simulation.
• Estimated thermodynamic factors using the PC-SAFT equation of state.
• Computed Fick diffusivities as the product of MS diffusivity and the thermodynamic factor.

Main Results:

• Achieved average deviations of 26% for CO2/n-decane and 15% for CO2/n-hexadecane compared to experimental data.
• Successfully predicted Fick diffusivities for CO2 with heavier n-alkanes (nC22, nC28, nC44).

Conclusions:

• Molecular simulation offers a viable alternative to experimental methods for determining Fick diffusivities.
• The proposed method is applicable to high-pressure systems and multicomponent mixtures, reducing experimental costs.