The Taylor-Aris dispersion technique has been successfully employed in the Rochester laboratory to determine binary tracer diffusion coefficients in supercritical dense fluids that are liquid under ambient conditions. For fluids that are gaseous under ambient conditions, dispersion peak tailing arising from solute adsorption ont tube walls and from inappropriate pulse injection methods has been found to adversely affect the accuracy of the diffusivity measurement. To redress these problems, tube surface deactivation and pulse injection under conditions identical to those prevailing in the dispersion tube are proposed. The modified technique will be used to gather diffusion coefficients of benzene, naphthlene, phenanthrene and 1,2-benzanthracene in near-critical and supercritical dense carbon dioxide, nitrous oxide, chlorotrifluoromethane and ethane. The results should permit a rough-hard-sphere theory of molecular diffusion to be tested in the supercritical dense region. Diffusion data in the near- critical region should place theories of dynamic critical phenomena in a broader perspective as the gas-liquid critical state is approached.
