Final Exam - Winter 1995

(15 pts)
1) The reaction

A -> B

is carried out inside spherical catalyst pellets of two different sizes. The effectiveness factor for pellet size A is 0.8 and for size B it is 0.4. Catalyst pellet B is 1 mm in diameter.

(a) At the mid point in each catalyst (i.e. = 0.5) what is the midpoint concentration (CA @ = 0.5) in catalyst A to the mid point concentration in catalyst B?

(b) What is the size of catalyst A?

(15 pts)
2) A reversible, exothermic, gas phase reaction has been studied in a packed bed reactor surrounded by a cooling jacket which holds the ambient temperature at 525 K. The data collected below indicate conditions down the length of the reactor for two different inlet temperature conditions.

What causes the peak in the temperature curves?
Why does the location of the peak change with inlet temperature?
The low temperature case has a fairly steady conversion increase down the reactor, whereas the high temperature case achieves most of its conversion in the first 25% of the reactor. Can you explain why this is so and what is the limiting factor for each case?

T0 (K)	Tmax (K)	W(Tmax)* (kg)	Xfinal
525	575	11.25	0.67
675	725	2.5	0.89

*-Position in the reactor at which the temperature peak occurs.

(30 pts)
3) The reaction

A + B -> C

is carreid out on a zeolite catalyst. The following data was obtained in a differential reactor.

Run	-rA mol/kg cat-min	PA (atm)	PB (atm)	PC (atm)
1	0	0	1	5
2	0	1	0	0
3	1.19	10	10	10
4	0.8	1	1	1
5	0.1	0.1	0.1	0.1
6	0.59	1	5	0
7	0.59	5	1	0
8	0.8	1	1	0
9	0.045	10	0.1	0
10	0.045	0.1	10	0

(a) Suggest a rate law and a mechanism, with a rate limiting step consistent with the experimental data.
(b) Determine the CSTR catalyst weight necessary to process a total molar feed of A and B of 100 moles/min and achieve 90% conversion. The entering partial pressure of A is 10 atm and the feed is equal molar in A and B.

(30 pts)
4) POLYMATH The irreversible, endothermic elementary, liquid phase reaction

2A -> B

is carried out adiabatically in a 100 dm³ PFR> Species A is fed to the reactor at a rate of 20 moles/min. The concentration of pure A is 3 mol/dm³. An inert stream is also fed to the reactor. The concentration of pure inert is also 3.0 mol/dm³. The entering temperature is 400K.

FA0 = 20 moles/min
CA0 = 3 moles/dm³
CI0 = 3 moles/dm³

(a) Show that CA01 = CA0/(1+I)

(b) First write out a POLYMATH program

(c) What is the ratio of the entering molar flow rate of inerts to enter molar flow rate of A, i.e. (I = FI0/FA0) at which the conversion is a maximum? What is the maximum conversion? Hint (0.5 < I < 1.5)

Additional Information:
k = 0.0003 dm³/mol/min at 300K
E = 12,000 cal/mol/K
CpA = 10 cal/mol/K (species A)
CpB = 20 cal/mol/K (species B)
CpI = 40 cal/mol/K (Inert)
HR = 10,000 cal/mol/K

(30 pts)
5) The elementary gas phase irreversible reaction

2A -> 2B

is carried out in a moving bed reactor in which there is significant pressure drop. Pure A enters the reactor at a concentration of 0.1 mol/dm³ and a flow rate of 2 mol/min. The entering pressure is 10 atm and the pressure at the exit is 4.472 atm. The catalyst decay is zero order. The catalyst loading rate is 10 kg/min and the catalyst bed contains 40 kg of catalyst. What is the conversion at the exit of the reactor?

Additional information:
Specific reaction rate kR = 20.0 dm⁶/(mol-kg cat-min)
Decay Constant kD = 0.25/min

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