Additional Homework Problems

CDP10-UB

  The cracking of normal paraffins (Pn) can be modeled as
   

image 10eq27.gif

     
    with surface reaction as the rate-limiting step. The rate of reaction has been found to increase with increasing temperature up to a carbon number of 15 (i.e.,) [J. Wei, Chem. Eng. Sci., 51, 2995 (1996)]. The rate was found to decrease with increasing temperature for a carbon number greater than 16. The reactions are carried out at sufficiently high temperatures that
     
   

image 10eq29.gif

     
    Plot the heat of adsorption (i.e.,10eq30.gif) and the apparent activation energy E * as a function of carbon number. Suggest an explanation for the unusual temperature dependence discussed above.
image 10eq31.gif
     
    The value E n appears to be independent of carbon number.

[J. Wei, Chem. Eng. Sci., 51, 2995 (1996)]