Measurement And Correlation On Infinite Dilution Diffusion Coefficients In High-Pressure And Supercritical Ethanol

Diffusion coefficients which associate with many physical property parameters of fluids, are base data in scientific research as well as in such other fields as engineering development and process planning. At present, diffusion theory can predict diffusion coefficients of gases accurately. However, because of complicated interaction between molecules, there are many methods to calculate the diffusion coefficients of liquids and supercritical fluids, moreover, these prediction methods have different theoretical principle, therefore, it is very difficult to predict diffusion coefficients of liquids and supercritical fluids by theoretical models. Additionally, the experimental data on diffusion coefficients of liquids and supercritical fluids is scarce relatively. Firstly, the developments of theoretical study and experimental determination of diffusion coefficients are briefly reviewed in this paper. On the basis of Taylor dispersion theory and liquid chromatography, an apparatus of liquid chromatograph has been designed and constructed. It can be used to measure the infinite dilution diffusion coefficients under high pressure. By examination with standard system, it was verified that the apparatus is reliable. Secondly, the infinite dilution diffusion coefficients have been determined for five organics: benzene, toluene, naphthalene, pyridine and p-nitroaniline under conditions of high pressure, nearcritical region and supercritical region. According to experimental results, four correlation models such as Wilke-Chang equation, Yang-Ma-Chen equation, He-Yu equation have been used to calculate the diffusion coefficients in ethanol under same conditions. In addition, Sun-Chen equation was employed to correlate infinite dilution diffusion coefficients of naphthalene and p-nitroanisole in nearcritical and supercritical ethanol. Finally, effect of temperature, pressure,hydrogen bond and solvent polarity on infinite dilution diffusion coefficients was analyzed and discussed. Particularly the influence of association through inter- molecular and intramolecular hydrogen bond was discussed. Solvent density inhomogeneities, cluster theory and changes of solvent polarity were introduced to explain the anomalous behavior of diffusion coefficients. In addition, the calculation results by four equation which are applicable to polarity system were selected for comparison.