Compressibility of Confined Fluids from Volume Fluctuations.

Area of Science:

• Materials Science
• Chemical Engineering
• Geophysics

Background:

• Fluid properties in nanopores differ significantly from bulk.
• Compressibility is a key mechanical property of fluid-saturated porous solids.
• Understanding confined fluid behavior is crucial for energy resource exploration, such as coal-bed methane and shale gas.

Purpose of the Study:

• To develop a novel molecular simulation method for calculating the compressibility of confined fluids.
• To apply this method to methane confined within carbon nanopores.
• To investigate the impact of pore size on fluid compressibility.

Main Methods:

• Utilized a molecular simulation approach based on volume fluctuations in the isothermal-isobaric ensemble.
• Employed integrated potentials to enable calculations.
• Achieved a simulation speed more than an order of magnitude faster than traditional Monte Carlo methods.
• Enabled calculations for pore sizes up to 100 nm.

Main Results:

• Predicted a fourfold increase in methane's bulk modulus within 3 nm slit carbon nanopores.
• Observed a gradual decrease in this enhancement as pore size increased.
• Found that at 100 nm pore size, the deviation from bulk compressibility was less than 5%.

Conclusions:

• The developed molecular simulation method is efficient and accurate for determining confined fluid compressibility.
• Fluid compressibility in nanopores is highly dependent on pore size, with significant deviations from bulk behavior at smaller scales.
• Findings have implications for the mechanical properties of porous materials and fluid recovery processes.