Determination of the Diffusion Coefficients of Binary CH 4 and C 2 H 6 in a Supercritical CO 2 Environment (500–2000 K and 100–1000 atm) by Molecular Dynamics Simulations

The self-diffusion coefficients of carbonaceous fuels in a supercritical CO 2 environment provide transport information that can help us understand the Allam Cycle mechanism at a high pressure of 300 atm. The diffusion coefficients of pure CO 2 and binary CO 2 /CH 4 and CO 2 /C 2 H 6 at high temperatures (500 K~2000 K) and high pressures (100 atm~1000 atm) are determined by molecular dynamics simulations in this study. Increasing the temperature leads to an increase in the diffusion coefficient, and increasing the pressure leads to a decrease in the diffusion coefficients for both methane and ethane. The diffusion coefficient of methane at 300 atm is approximately 0.012 cm 2 /s at 1000 K and 0.032 cm 2 /s at 1500 K. The diffusion coefficient of ethane at 300 atm is approximately 0.016 cm 2 /s at 1000 K and 0.045 cm 2 /s at 1500 K. The understanding of diffusion coefficients potentially leads to the reduction in fuel consumption and minimization of greenhouse gas emissions in the Allam Cycle.