Page 99 - The engineering of chemical reactions

Problems 83

(c) What do we have to be concerned with regarding reactor construction materials and pressure
relief capabilities to design for this possibility?
2.12 We wish to produce B in the reaction system

A+ B, r-1 = klCA
A + C, r2 = k2Ca

A costs $1.20/lb, B sells for $2.50/lb, and C costs $0.50/lb to dispose.
(a) What relation between the ks will give a positive cash flow if the reactor and operating
costs are ignored?
(b) What relation between the ks will give a 30% profit on sales if the reactor and operating
costs are ignored?

2.13 Sterilization is a batch process by which bacteria and molds in food are killed by heat treatment.
A can of vegetables that originally contained 10,000 viable spores has 100 spores remaining
after heating for 10 min at 250°F. Assuming first-order kinetics, how long must this can be
heated at this temperature to reduce the probability of having a single spore to an average of 1
in 1 million cans?

2.14 Methanol is synthesized commercially from CO and Ha by the reaction

CO + 2H2 2 CHjOH
over a Cu/ZnO catalyst at -350°C at 50-100 atm. The standard-state thermodynamic data on
this reaction are AHRq2as = -90.64 kI/mole and AG&ss = -24.2 kI/mole.
(a) What is the equilibrium conversion of a stoichiometric mixture of CO and Ha to methanol
at 298 K at 1 atm?
(b) Assuming AH’ independent of T, what are K,, and the equilibrium conversion at 1 atm
and 35O”C?
(c) The actual value of Kes at 350°C is 1.94 x 10P4. How large is the error assuming constant
AH?
(d) At what pressure will the equilibrium conversion be 50% at 35O”C?

2.15 A fluidized-bed catalytic cracker operates nearly adiabatically. In the reactor, all cracking
and dehydrogenation reactions are strongly endothermic, while in the regenerator, strongly
exothermic oxidation reactions occur. Set up an energy balance for the reactor and regenerator
assuming a highly simplified set of reactions
=Cl6&8 + =GHls + n-%H16
n-Ci6H3s + 16C + 19Hz
c+o2 + co2

(a) What fraction of the hydrocarbon must form coke for the overall reactor to be adiabatic?
Heats of formation of n-C16Hss, n--CsHls, and rz-CsHl6 are -89.23, -49.82, and -19.82
in kcal/mole, respectively, and A HR of CO oxidation is -94.05 kcal/mole.
(b) Indicate how you would determine the energy balance for a catalytic cracker knowing the
feed and product composition of the reactor.