Chapter 6: Isothermal Reactor Design: Molar Flow Rates

Additional Homework Problems

CDP6-30D

The decomposition of cumene

is to be carried out at a high temperature in a packed-bed reactor. At this temperature the reaction is internal diffusion limited and first-order in cumene. Currently, 1000 kg of catalyst is packed in a 4 cm diameter pipe. The catalyst particles are 0.5 cm in diameter and the bulk density of the packed catalyst is 1000 kg/m3. Currently, 6.4% conversion is realized when pure cumene enters the reactor. The entering pressure is 20 atm and the pressure at the exit of the reactor is 2.46 atm.

  1. What conversion would be achieved if the PBR were replaced by a fluidized CSTR containing 8000 kg catalyst with negligible pressure drop?

  2. We know from DVD Chapter 12 that for internal diffusion limitations, the rate of reaction varies inversely with catalyst particle size. consequently, one of the engineers suggests that the catalyst be ground up into a smaller size. She also notes there are three other pipe sizes available into which the catalyst could be packed. These noncorrosive heat-resistant pipes, which can be cut to any length, are 2 cm, 6 cm, and 8 cm in diameter. Should you change the catalyst size and pipe diameter in which the catalyst is packed? If so, what are the appropriate catalyst particle size, the appropriate pipe diameter, and the exiting conversion? If nothing should be changed, explain your reasoning. Assume that the flow is highly turbulent and the bulk catalyst density is the same for all catalyst and pipe sizes. Explain how your answers would change if the flow were laminar.

  3. Discuss what you learned from this problem and what you believe to be the point of the problem.

[3rd Ed. P4-20]