Chapter 9, Problem 9.32P

Cumene (C₆H₅C₃H₇) is produced by reacting benzene with propylene $\left[\Delta H_r^{°}\left(77°F\right)=-39,520Btu\right]$.

A liquid feed containing 75 mole% propylene and 25% n-butane and a second liquid stream containing essentially pure benzene are fed to the reactor. Fresh benzene and recycled benzene, both at 77°F. are mixed in a 1:3 ratio (1 mole fresh feed/3 moles recycle) and passed through a heat exchanger, where they are heated by the reactor effluent before being fed to the reactor. The reactor effluent enters the exchanger at 400°F and leaves at 200°F. The pressure in the reactor is sufficient to maintain the effluent stream as a liquid.

After being cooled in the heat exchanger, the reactor effluent is fed to a distillation column (T1). All of the butane and unreacted propylene are removed as overhead product from the column, and the cumene and unreacted benzene are removed as bottoms product and fed to a second distillation column (T2) where they are separated. The benzene leaving the top of the second column is the recycle that is mixed with the fresh benzene feed. Of the propylene fed to the process, 20% does not react and leaves in the overhead product from the first distillation column. The production rate of cumene is 1200 Ib_m/h.

1. Calculate the mass flow rates of the streams fed to the reactor, the molar flow rate and composition of the reactor effluent, and the molar flow rale and composition of the overhead product from the
first distillation column, Tl.

Calculate the temperature of the benzene stream fed to the reactor and the required rate of heat addition to or removal from the reactor. Use the following approximate heal capacities in your calculations: $C_p\left[Btu/\left(I{b}_m\cdot °F\right)\right]=0.57$for propylene. 0.55 for butane. 0.45 for benzene, and 0.40 for cumene.

Most people unfamiliar with the chemical process industry imagine that chemical engineers are people who deal mainly with chemical reactions carried out on a large scale. In fact, in most industrial processes,

a visitor to the plant would have trouble finding the reactor in a maze of towers and tanks and pipes that were added to the process design to improve the profitability of the process. Briefly explain how the heat exchanger, the two distillation columns, and the recycle stream in the cumene process serve that function.