Molecular dynamics investigation on the infinite dilute diffusion coefficients of organic compounds in supercritical carbon dioxide

A new approach to represent the infinite dilute diffusion coefficients D-12 (infinity) of organic compounds in supercritical carbon dioxide by molecula r dynamics simulation from the molecular specific constants was proposed. F rom the experimental critical constants of organic compounds or critical co nstants estimated by Joback-Lydersen methods and the equation of state of L ennard-Jones fluid, new Lennard-Jones parameters of 38 organic compounds we re obtained according to the corresponding state principle. With these para meters, D-12(infinity) for some high-value-added biochemical and pharmaceut ical compounds in supercritical carbon dioxide at 313.15 K and 16.0 MPa wer e predicted for the first time by molecular dynamics simulation with simple combining rules. Without any adjustable parameters, the accuracy of predic tion reached the qualitative or semi-quantitative level. The effects of com bining rules on the simulation results were also reported. It was shown tha t the empirical combining rule proposed by the authors (ZLWS) sigma(12) = ( 1/4)sigma(11) + (3/4)sigma(22), epsilon(12) = root epsilon(11)epsilon(22) p redicted more precisely than the Lorentz-Berthelot combining rule did. It w as also found that D-12(infinity) Of Organic compounds in supercritical car bon dioxide were highly related with the critical constants. A new empirica l equation D-12(infinity) = 6.58 x 10(-8) (T-c/P-c)(-0.3471) for D-12(infin ity) of organic compounds in supercritical carbon dioxide at 313.15 K and 1 6.0 MPa was proposed. This equation has a simple form and good predictive f unction. (C) 2000 Elsevier Science B.V. All rights reserved.