Experimental Nonisothermal Effectiveness Factors

In Sec. 11-7, Eq. (11-59) was developed as a criterion for deciding if intrapellet mass transport had a significant effect on the rate. Weisz and Hicks have extended the analysis to the problem of combined mass and energy transport. For a first-order irreversible reaction the criterion may be expressed as 

The magnitude of intrapellet temperature differences and nonisothermal 7] are illustrated by the following examples, based on experimental measurements for specific systejns. 

Example 11-9 Rarf data for the reaction -1- jOj HjO have been measured-for single catalyst pellets (1.86-cm diameter) of platinum on AljOj. Catalyst properties, kg, Dg, and center and surface temperatures were also evaluated. The rate was obtained in a stirred-tank reactor in which the pellet was surrounded by well-mixed reaction gases. In one run the data were as follows  

Rate data were also obtained for the small (80 to 250 mesh) particles from which the pellets were prepared. The results, expressed as the rate of oxygen consumption, g moles/(g catalyst)(sec), were correlated by 

Solution Equation (11-83) will be satisfactory as a criterion, since the I -vs-77 curves for a first-order reaction will be nearly the same as those for 0.8 order  

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Table 9.1 shows some of the experimental and assumed values of the parameters considered for catalytic oxidation of CH3OH to CH20 with 13 = 0.0109 and hence display relatively fewer nonisothermal effects. The thermal diffusion coefficient is usually smaller by a factor of 102—103 than the ordinary diffusion coefficient for nonelectrolytes and gases. Therefore, for the present analysis the values for e and co are assumed to be 0.001. 

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