King Saud University
CHE426
College Of Engineering
Time 90 Min
Chemical Eng. Dept.
Date 3/5/1428 H
---------------------------------------------------------------------------------------Instruction : attempt all question
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Question One
The zero-order reaction A
B is carried out in a moving-bed
reactor containing 1 kg of catalyst. The catalyst decay is also zero-order.
The entering molar flow rate is pure A at 1 mol/min.
Given the following information:
- The product sells for SR 800 per gram mole.
- The cost of operating the bed is SR 50 per kilogram of
catalyst exiting the bed.
(a) Sketch the catalyst activity as a function of catalyst weight down
the reactor length for a catalyst feed rate of 30 kg/min.
(b) What is the feed rate of solids (kg/min) that will give the
maximum profit?
(c) What are the activity and conversion exiting the reactor at this
optimum?
Addition information:
Specific reaction rate: kr = 1.0 mol/kg cat. Min
Decay constant : kd = 2.0 min-1
Question Two
The catalytic cracking of gas oil is to be carried out in a moving -bed
reactor at 480 C, this reaction can be written as A ----------- products
with a second-order rate law with the following specific reaction rate
- rA’ = k CA2 , k= 0.6 ( (dm)6 / (g cat. mol min ) . The catalytic
deactivation is independent of gas-phase concentration and follows a
first-order decay rate law, with a decay constant of 0.7 min –1.The feed
stream is diluted with nitrogen. The reactor contains 22 kg of catalyst
that moves through the reactor at a rate of 10 kg/min. The gas oil is fed at
a rate of 30 mol/min at a concentration of 0.075 mol/dm3.
Determine :
1- the conversion that can be achieved in this reactor ,
2- the activity of the catalyst out from the reactor.
Question Three
The reversible isomerization of compound A
B is
carried out over a supported metal catalyst in an isothermal fixed bed
flow reactor. A and B are liquid, the equilibrium constant for the reaction
is 8.5 at 350 ºF and 0.6 at 400 ºF. The catalyzed reaction is pseudo-firstorder in A. Side reaction have a negligible effect on yield, but they slowly
deactivate the catalyst.
1- Derive an equation shows how the temperature of the catalyst reactor
should be increased with time in order for the reaction rate to remain
unchanged.
2- Determine the temperature-time trajectory (from 440 K to 480 K) to
keep conversion constant in a CSTR if the catalyst decay is first-order,
with a decay constant (kd) = 6.0 *10-3 hr-1 at 440 K. Activation energies
for reaction and decay are 30 kcal/mol and 10 kcal/mol, respectively