The Experiment Measurement And Molecular Dynamics Simulation Of Diffusion Coefficients In Supercritical CO₂

Diffusion coefficients of fluids which associate with many physical property parameters of fluids are base data for scientific research, engineering development and process planning. Because of complication in interaction between molecules, it is very difficult to predict diffusion coefficients of fluids by theoretical models. The experimental data on diffusion coefficients of liquids and supercritical fluids is hard difficult to measure because of rigorous experimental condition.A measurement based on Supercitical Chromatography and the Taylor dispersion principles was carried out to determine the infinite dilute diffusion coefficients of methanol and ethanol in the supercritical CO2. The experimental data were used to compare the MD data.Molecular dynamics simulation chose COMPASS force field and periodic boundary conditions; the equilibration course adopted NPT ensemble, and the analytical course adopted NVE ensemble. The self-diffusion coefficients of supercritical CO2 were studied and the suitable parameters were chosen by analyzing cut-off distance, time step, time, and molecular numbers. It was shown that MD simulation could predict the self-diffusion coefficients of supercritical carbon dioxide precisely. The infinite dilute diffusion coefficients of benzene and naphthalene were calculated by MD simulation. By the comparison of literature experiment and MD simulation data, the calculation results showed good agreements with literature data. In this work, the results of the MD simulation of the infinite dilute diffusion coefficients of methanol and ethanol behaved good accordance with literature data. By the comparison of experiment and MD simulation data, it was denoted that the simulation values were highly consistent with the experiment data and literature data. Therefore, molecular dynamics method could calculate the self-diffusion coefficients of supercritical CO2 and the infinite dilute diffusion coefficients of polar and nonpolar solutes in supercritical CO2 accurately. MD simulation would help experiment devise and engineering application of supercritical CO2.