Steady-state parallel plate apparatus for measurement of diffusion coefficient in supercritical carbon dioxide

A new, steady-state experimental system for measurement of the Fickian diff usion coefficients for solutes in supercritical carbon dioxide (SC-CO2) was designed and evaluated. Mass transfer between a Liquid solute and SC-CO2 w as carried out in a parallel plate geometry where a porous metal sheet, imm ersed in the liquid phase, stabilized the interface. The SC-CO2 flowed over the porous metal sheet containing the liquid phase which was presaturated with CO2. The use of the porous metal sheet and a thin mobile layer allowed now rates high enough to achieve the necessary pressure drop to eliminate the commonly encountered, density-induced stagnation of SC-CO2 at the inter face while avoiding surface-tension-related problems. The binary diffusion coefficients of methyl oleate in SC-CO2 at finite concentrations were measu red at 40, 50, and 60 degrees C and at pressures ranging from 10.6 to 14.0 MPa. The experimentally measured values were 1.5-4.6 times lower than those predicted for infinite dilution and were found to decrease with solute con centration at constant pressure and temperature. This technique offers adva ntages over other commonly used methods in that the concentration dependenc e of diffusion coefficients in multicomponent systems can be studied.