Ideal Flow Reactors - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 248

(d) a constant-pressure CSTR.
(e) Calculate the residence times and space times in these reactors.
5.18. One hundred moles of A per hour are available in concentration of 0.1 mol/L by
a previous process. This stream is to be reacted with B to produce C and D. The reaction
proceeds by the aqueous-phase reaction,

; k ¼ 5 L $ mol 1 $ h 1

A þ B / C þ D

The amount of C required is 95 mol/h. In extracting C from the reacted mixture A and B
are destroyed; hence recycling of unused reactants is not possible. Calculate the
optimum reactor size and type as well as feed composition for this process.
Data: B costs $1.25/mol in crystalline form. It is highly soluble in the aqueous solu-
tion and even when present in large amounts does not change the concentration of A in
solution. Capital and operating costs are $0.015/h/L for mixed-flow reactors.
5.19. One-hundred and fifty moles of B are to be produced hourly from a feed consisting of
a saturated solution of A ( C A0 ¼ 0.1 mol/L) in a mixed-flow reactor. The reaction is

r ¼ 0:2 h 1 C A

A / B ;

The cost of reactant at C A0 ¼ $0.50/mol A. The cost of reactor

including installation, auxiliary equipment, instrumentation, overhead, labor, depreci-
ation, etc., is $ m

0.1 mol/L is $A ¼

$ liter 1 .
What reactor size, feed rate, and conversion should be used for optimum operations?
What is the unit cost of B for these conditions if unreacted A is discarded?
5.20. Suppose all unreacted A of the product stream of the previous problem can be
reclaimed and brought up to the initial concentration C A0 ¼

$0.01 h 1

¼

0.1 mol/L at a total cost of
$0. A (125/mol) processed. With this reclaimed A as a recycle stream, find the new
optimum operating conditions and unit cost of producing B.
5.21. Consider the reaction

; r ¼ 0:15 min 1 C A
in a CSTR. A costs $2/mol, and B sells for $4/mol. The cost of operating the reactor is
$0.03 per liter per hour. We need to produce 100 mol of B/h using C A0 ¼

A / B

2 mol/L.

Assume no value or cost of disposal of unreacted A.
(a) What is the optimum conversion and reactor size?
(b) What is the cash flow from the process?
(c) What is the cash flow ignoring operating cost?
(d) At what operating cost do we break-even?
5.22. Find an expression for the conversion in a dimerization reaction
2 A ; r ¼ kC 2 A

with A and B ideal gases starting with pure A at 1 atm in
(a) a CSTR,
(b) a PFR.
5.23. Find an expression for the conversion in a dimerization reaction
2 A

/ B

r ¼ kC 2 A

/ ;

B