MOLECULAR-DIFFUSION COEFFICIENTS AND EFFECTIVE DIFFUSIVITIES OF 1-OCTENE IN SUPERCRITICAL ETHANE IN RELATION TO FISCHER-TROPSCH SYNTHESIS

Fischer-Tropsch synthesis employing supercritical fluid reaction media offers mass transfer advantages over conventional processes. Data are needed to calculate effective diffusivities in catalyst pores, for wh ich molecular diffusion coefficients in the supercritical media as wel l as the catalyst porosity and tortuosity are required. The Taylor dis persion technique was used to measure the molecular diffusion coeffici ents. A tracer response technique was used to measure the effective di ffusivities employing 1-octene in supercritical ethane (P-c = 48.8 bar , T-c = 305.4 K) as the model system with an iron-based Fischer-Tropsc h catalyst. Measurements were made in the temperature range of 523-543 K and pressure range of 62-144 bar. The results were analyzed by the subtraction of moments method. The precision of the results is within approximately 15%. The average value of tortuosity divided by particle porosity (tau/epsilon(p)) is (9.72 +/- 1.22), while the average value of tau is (6.10 +/- 0.766) using the particle porosity set at 0.628.