Calculation of Mutual Diffusion Coefficients near the Critical Region from the Peng−Robinson Equation of State

Abstract

We observed that the mutual diffusion coefficients of benzene in supercritical carbon dioxide exhibited a maximum at pressures above the critical pressure of the mixture, and a strong concentration dependence near the critical point. These surprising experimental results can be explained by replacing the concentration gradient of diffusion with a chemical potential gradient as suggested from irreversible thermodynamics. Then, it can be understood that diffusion coefficients have a maximum value at the critical point of a mixture. The Peng−Robinson equation of state was used to illustrate these relationships.

Fundamental behavior of benzene–CO2 mutual diffusion coefficients in the critical region of CO2

“…Our calculation results [16] combined with the Peng-Robinson EOS for Q show a V-shape for the trend of diffusion coefficients against pressure in the critical region. Unfortunately, our previous work was limited to pressures higher than the critical pressure to avoid the possibility of vapor-liquid phase separation.…”

“…In our previous work [14][15][16][17], when we reported on the measurement of mutual diffusion coefficients of acetone [14] or benzene [15] in carbon dioxide at pressures higher than the critical pressure, we observed astonishing phenomena in which diffusion coefficients decreased at conditions near the critical point of the mixture.…”

Solubilities and diffusion coefficients of high boiling compounds in supercritical carbon dioxide

“…Thus, several correlation equations for diffusion coefficients in supercritical fluids are generally based on condition at infinite dilution. Near the spinodal curve, there appears to be a decrease in the diffusion coefficient as shown by theoretical derivations and experimental measurements (Tsekhanskaya, 1971;Dysthe and Hafskjold, 1995;Nishiumi et al, 1996;Ago and Nishiumi, 1998). There may be consideration of concentration in the Taylor method as shown by Funazukuri et al (2000a).…”

“…represented by their equations (Clifford and Coleby, 1991;Bartle et al, 1991a;Dysthe and Hafskjold, 1995;Nishiumi et al, 1996;Ago and Nishiumi, 1998).…”

Direct calculation of mutual diffusion coefficients of binary system using non-equilibrium molecular dynamics simulation

“…Many data of mutual diffusion coefficients for binary system have been reported in the single phase region. The mutual diffusion coefficients are known to have anomalous concentration dependence in the vicinity of critical point of vapor-liquid equilibria (VLE) and at supercritical conditions [1][2][3][4][5][6][7][8]. Such anomalous behavior may appear by the chemical potential (activity and fugacity) gradient which can be represented by a thermodynamic factor [9][10][11][12].…”