Determination of diffusivities of triolein in pressurized liquids and in supercritical CO2

Abstract

Pressurized liquid extraction and supercritical fluid extraction are attracting attention. The accurate design and scale-up of these processes need the knowledge of transport property, namely, diffusion coefficients. In this study, the measurements of diffusion coefficients D12 of triolein with a high molecular weight were carried out in pressurized fluids with different viscosities. The D12 values in various pressurized liquids of ethanol, methanol, and hexane were determined by the Taylor dispersion method at 298.15 to 323.15 K and pressures of 1.00 to 12.08 MPa. We found that the D12 data in supercritical CO2 cannot be accurately measured by the Taylor dispersion method because the response peaks of triolein in supercritical CO2 obtained by the Taylor dispersion method were severe tailing. However, the tailings were significantly improved by using the chromatographic impulse response method. Therefore, the D12 values in supercritical CO2 were measured by the chromatographic impulse response method at 303.15 to 333.15 K and pressure up to 31.02 MPa. The magnitude of determined D12 of triolein in fluids is in the order of CO2 > hexane > methanol > ethanol. The D12 increased from 0.306 × 10−9 m2 s−1 at 298.15 K and 10.00 MPa in liquid ethanol to 6.323 × 10−9 m2 s−1 at 333.15 K and 13.77 MPa in supercritical CO2. All the diffusivity data of triolein measured in CO2, hexane, methanol, and ethanol in this study can be satisfactorily represented by the hydrodynamic equation over a wide range of fluid viscosity of 37 to 1179 μPa s from liquid to supercritical states.