Biomedical Engineering Reference
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(c)
The actual process produces about 0.8 mol of ethylene per mole of ethane fed (the
yield of the process is 80%). What is the cash flow of the process? What must be the
cost of producing ethylene if we want a profit of 10% of sales?
3.22. Estimate the amount of CO
2
you will produce every time you fill your gasoline tank.
Assume 55 L of octane with a density of 680 kg/m
3
. How much CO
2
does your car
liberate into the atmosphere each year assuming one fill-up every 2 weeks? Would it
make any difference to the environment if you switch to a fuel that is produced from
wheat straw and why?
3.23. We wish to produce B in the reaction system
A
/
B
þ
C
;
r
1
¼
k
c
A
1
2
A
/
D
;
r
2
¼
k
c
A
2
(a)
What is the rate of formation of B?
(b)
What is the disappearance rate of A?
(c)
What operating parameters (temperature, pressure, feed rate, and feed
concentrations) can one change to optimize the system?
(d)
If A costs $0.10/mol, B sells for $0.25/mol, C and D cost $0.05/mol to dispose, what
relation of the k's will give a 20% profit on sales? Neglect the cost to reactor and
operation.
3.24. We wish to produce B from the reaction:
A
/
;
r
1
¼
k
c
A
B
1
Unfortunately, A also decomposes to form a by-product C
A
/ 2
C
;
r
2
¼
k
c
A
2
A costs $1.00/lb, B sells for $3.00/lb, and C costs $0.80/lb to dispose. Neglect the
reactor and operating costs.
(a)
What relation between the k's will give a positive cash flow?
(b)
What relation between the k's will give a 25% profit on sales?
3.25. We wish to produce R from the reaction:
c
1:
A
2
A
/
R
þ
P
;
r
1
¼
k
1
Unfortunately, A also reacts to produce a by-product Q
c
1:
A
A
/
Q
;
r
2
¼
k
2
A costs $1.00/mol, R sells for $3.80/mol, while P and Q cost $0.50/mol to dispose.
Neglect the reactor and operating costs.
(a)
What relation between the k's will give a positive cash flow?
(b)
What relation between the k's will give a 50% profit on sales?
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