MEASUREMENT OF THE DIFFUSION-COEFFICIENTS OF ACETONE, BENZENE, AND ALKANE IN SUPERCRITICAL CO2 BY THE TAYLOR DISPERSION METHOD

An apparatus for the measurement of the diffusion coefficient of supercritical fluids has been constructed based on the principle of the Taylor dispersion method. The present apparatus uses a 1.2-m long straight capillary tube for the diffusion tube, in which use of two concentration detectors having no dead volumes eliminates initial dispersion, and a position-sensitive detector with a He-Ne laser in order to detect the solute concentration. The diffusion coefficients of acetone, benzene, and alkane (C5H12 to C14H30) in CO2 have been measured at temperatures 26-35-degrees-C and pressures 9-10.5 MPa. The maximum uncertainty of the present results was estimated to be +/- 3%. For alkane (C5H12 to C14H30), the temperature dependence was found as positive and concave near the critical temperature. The molecular-weight dependence of the diffusion coefficients was negative, and the diffusion coefficient Of C5H12 in CO2 was about 1.4 times as large as that of C14H30 at the same conditions.