Molecular Dynamics Simulation of the Thermal Diffusion Effect in n-Alkane Binary Mixtures

Area of Science:

• Thermodynamics
• Chemical Engineering
• Materials Science

Background:

• Thermal diffusion causes compositional variations in hydrocarbon fluids within oil and gas reservoirs.
• Molecular dynamics (MD) simulations offer a broader pressure and temperature range for studying thermal diffusion compared to experimental methods.
• Previous MD studies on n-alkane binary mixtures were limited to specific, shorter-chain alkanes.

Purpose of the Study:

• To investigate the thermal diffusion effect in a wider range of n-alkane binary mixtures using molecular dynamics simulations.
• To establish a reliable and repeatable workflow for molecular simulations of thermal diffusion.
• To compare simulation results with experimental data and validate the simulation approach.

Main Methods:

• Utilized boundary-driven nonequilibrium molecular dynamics (BD-NEMD) with the enhanced heat exchange (eHEX) algorithm.
• Performed MD simulations on various n-alkane binary mixtures (C1-C3, C1-nC4, nC7-nC12, nC7-nC16, nC10-ni) under diverse conditions.
• Developed and implemented a workflow to ensure the repeatability and reliability of molecular simulations for thermal diffusion.

Main Results:

• Simulations covered a broad spectrum of n-alkane binary mixtures, including longer chains like nC7-nC16 and nC10-ni.
• The developed workflow demonstrated the repeatability and reliability of the MD simulations.
• Simulation results showed errors generally below 10% when compared with experimental data.
• Observed that heavier components migrate towards colder regions, while lighter components aggregate in hotter regions.

Conclusions:

• The study successfully extended MD simulations to a wider range of n-alkane binary mixtures.
• The findings confirm the tendency of heavier components to move to cold regions and lighter components to hot regions under thermal gradients.
• The proposed workflow enhances the reliability of MD simulations for studying thermal diffusion effects in hydrocarbon mixtures.