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

Tuan, DQ
Yener, Meryem Esra
Zollweg, JA
Harriott, P
Rizvi, SSH
A new, steady-state experimental system for measurement of the Fickian diffusion coefficients for solutes in supercritical carbon dioxide (SC-CO2) was designed and evaluated. Mass transfer between a Liquid solute and SC-CO2 was carried out in a parallel plate geometry where a porous metal sheet, immersed 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 interface while avoiding surface-tension-related problems. The binary diffusion coefficients of methyl oleate in SC-CO2 at finite concentrations were measured 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 concentration at constant pressure and temperature. This technique offers advantages over other commonly used methods in that the concentration dependence of diffusion coefficients in multicomponent systems can be studied.