Molecular Simulation Study on the Density Behavior of n-Alkane/CO₂ Systems.

Area of Science:

• Physical Chemistry
• Chemical Engineering
• Materials Science

Background:

• Understanding the volumetric behavior of hydrocarbon mixtures with CO2 is crucial for applications like carbon sequestration and enhanced oil recovery.
• n-alkanes are common components in crude oil and natural gas, making their interactions with CO2 a key area of study.

Purpose of the Study:

• To investigate the density and volumetric properties of n-alkane/CO2 mixtures using molecular dynamics simulations.
• To elucidate the molecular-level mechanisms governing the compressibility and phase behavior of these mixtures under varying conditions.

Main Methods:

• Molecular dynamics simulations were employed to study hexane, octane, and decane mixed with CO2.
• Simulations were conducted across a temperature range of 303–363 K and pressure range of 3.8–8.67 MPa.

Main Results:

• System density initially increases then decreases with increasing CO2 mole fraction, with significant volume expansion above ~60% CO2.
• Compressibility is poor at low CO2 concentrations due to alkane packing, but increases significantly as CO2 forms a separate phase at higher concentrations.
• Longer alkane chains lead to reduced volume swelling and increased density due to stronger intermolecular forces.

Conclusions:

• The study provides a molecular-level understanding of n-alkane/CO2 mixture behavior, essential for optimizing carbon sequestration and CO2-enhanced oil recovery processes.
• Findings highlight how CO2 concentration, temperature, pressure, and alkane chain length influence mixture properties and molecular diffusion.