Chap. Questions and Problems 527

The feed to the reactor is equal molar in in both m-xylene and o-xylene (spe- cies A and B). For a total feed rate of 2 and the reaction conalitionsbelow, plot the temperature and the molar flow rates of each species as a func- tion of catalyst weight up to a weight of 100 kg. .

(a) Find the lowest concentration of o-xylene achieved in the reactor. (b) Find the highest concentration of m-xylene achieved in the reactor.(c) Find the maximum concentration of o-xylene in the reactor.(d) Repeat parts (a) to (d) for a pure feed of o-xylene.(e) some of the system parameters and describe what you learn.

What do you believe to be the point of this problem?

Additional information:

All heat capacities are virtually the same at

= 2

= -1800

= -1100

k , = 0.5 -

=

= 0.005 -

= 10 -

330 K

= 500 K

=

= 100

(Multiple reactions with heat effects) Styrene can be produced from zene by the following reaction:

ethylbenzene styrene +

ethylbenzene benzene + ethylene

several irreversible side reactions also occur:

ethylbenzene + toluene + methane (3)

[J. Snyder and B. Subramaniam,Chem. Eng. 49,5585

zene is fed at a rate of 0.00344 to a PFR (PBR) along withinert steam at a total pressure of 2.4 atm. The molar ratiois initially parts (a) to 14.5: 1 but can be varied. Given the following data, find the exiting molar flow rates of styrene, benzene, and toluene for the following inlet temperatures when the reactor is operated adiabatically.(a) = 800 K(b) = 930 K(c) = 1100 K

Obtained from inviscid pericosity measurements.

528 Steady-State Nonisothermal Reactor Design Chap, 8

Find the ideal inlet temperature for the production of styrene for a ratio of 58: 1. (Hint: Plot the molar flow rate of

stryrene versus Explain why your curve looks the way it does.)

(e) Find the ideal ratio for the production of styrene at 900 K. [Hint:See part (d).]

What do you believe to be the points of this problem?

(g) Ask another question or suggest another calculation that can be made forthis problem.

Additional information:

Heat capacities

Methane 68 K Styrene 273

Ethylene 90 K Ethylbenzene 299

Benzene 201 Hydrogen 30

Toluene 249 Steam 40

p =2137 of pellet

=0.4

= 118,000 ethylbenzene

= 105,200 ethylbenzene

= -53,900 ethylbenzene

= exp + + + atm

-2.314 X-17.34

=

b3 5.051

= 1.302

-4.931X

The kinetic rate laws for the formation of styrene benzene (B), and tolu- ene (T), respectively, are as follows. = ethylbenzene)

= p (1- exp 13.2392-

(1

The temperature T is in kelvin. The liquid-phase reactions

D (desired reaction)

A + B U (undesiredreaction)

Chap. Questions and Problems 529

are carried out in a perfectly insulated CSTR. The desired reaction is first order

in A and zero order in B, while the undesired reaction is zero order in and

first order in B. The feed rate is equimolar in A and B. Species A enters the

reactor at a temperature of 100°C and species B enters at a temperature of 50°C.

The operating temperature of the reactor is 400 K. The molar flow rate of A

entering the reactor is 60 = 20 K, = 30 K,= 50 and = 40

For reaction 1:

For reaction 2:

= -3000 of A at 300 K

= -5000 of A at 300 K

= 1000exp --

mol= 0.01 0.001-

(a) What will be the exit molar flow rates of and D from the reactor? (b) What is the CSTR reactor volume for the conditions specified above?

(c) Is there a more effective way to maximize D? Explain.(Hint: Start with a mole balance on A. Outline your method before beginning

any calculations.)

The liquid phase reactions

B D

can be carried out in a number of CSTRs. the following sizes are

available, 4 40 400 4000 ‘You can use up to 4 CSTRs of

any one size. The heat to each reactor is by adjusting the func-

tional area 1

Q, = - where the ambient temperature can be

varied between 0°C and 100°C.

.=

=

-

=

The Concentration of pure A is 5 M. A can be diluted with solvent. The feed

can be cooled to 0°C or heated to 100°C.

= +10,000 A

= -10,000 B

= -100,000 B