Estimation of Diffusion Coefficients in Liquids

7 Measurement of Reaction Kinetics and Effective Pellet Diffusivity in a Single-pellet Reactor 

The isomerization of n-hexane at 453° C and a total pressure of 1.6 bars has been investigated by Christoffel and Schuler [15]. They used a single pellet reactor with a pellet thickness L of 6.22 xlO-3 m. The porous pellet material contained 0.35 wt % Pt on A O,. The flow rate along the pellet was so high that the observed conversion rate was independent of the flow rate. The partial pressure of n-hexane in the feed was varied between 15 and 160 mbar. The ratio of the n-hexane concentration in the space below the pellet CAb and in the gas mixture above the pellet CAj was found to be independent of Caj CaJCa, = 0.191. The apparent conversion rate was found to be proportional to the n-hexane concentration in the feed and to be represented by RA = 0.184x0 krnol m 3 s 1. From these results the following information can be obtained  

Because the conversion rate is independent of the external flow rate, external diffusion limitations can be neglected. Both from the proportionality of the conversion rate with the feed concentration and the independence of CjJC from CAj it follows that the reaction is first order, so that = 1/cosh, RA = (tanh0)/0 and DtA = L2, / 2. 

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