# 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 -rAmol/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)

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?