Mass-transfer coefficients and equilibrium solubilities for fluid-supercritical-solvent systems by online near-IR spectroscopy

Abstract Mass-transfer coefficients and equilibrium solubilities for the systems α-tocopherol-carbon dioxide, isophytol-carbon dioxide, and dihydroisophytol-carbon dioxide were determined in the temperature range from 327 to 353 K and pressures up to 35 MPa. A rectangular, plain liquid film was used as mass-transfer surface. Reynolds numbers were varied between 100 and 3000 (laminar and transition flow region). Liquid concentrations in the supercritical solvent could be measured online by means of a fiber-optical near-IR spectrometer. The resulting mass-transfer coefficients could not be described by known Sherwood number correlations. Especially, the dependence on Schmidt numbers was completely unusual. Introducing a diffusion-hindering term into the usual dimensionless equation resulted in a correct correlation of the measured values for the investigated systems.