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Code No: R05310805
Set No. 1
III B.Tech I Semester Regular Examinations, November 2007
CHEMICAL REACTION ENGINEERING-I
(Chemical Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks

1. The activation energy for the decomposition of 2 5 is 24630 cal/g mole (103
kJ/mole).

(a) What will be the ratio of their rates at 00C and 250C (the rate being measured
at the same concentration of reactant)?
(b) If the rate constant of the reaction at 250C is 0.002 min-1 calculate the rate
constant for the reaction at 500C [8+8]
2. A constant density rst order reaction A P is carried out in a batch reactor.
Data obtained are given as:

Time(sec) 30 60 90 120 150 180 600
Concentration of A ( 3) 0.74 0.55 0.42 0.29 0.24 0.16 0.0025
If A0 = 1 3, calculate the rate constant for the reaction. Also calculate
time required for 50% conversion. [12+4]
3. (a) Find the rst order rate constant for the disappearance of A in the gas reac-
tion 2A R if, on holding the pressure constant, the volume of the reaction
mixture, starting with 80% A, decreases by 20% in 3 minutes.
(b) Explain the method of isolation and metho d of initial rates for the analysis of
batch reactor data. [10+6]
4. An aqueous feed containing A (1 mol/liter) enters a 2-liter plug ow reactor and
reacts away (2 - A = 0 05 2 A mol/liter.sec). Find the outlet concentration
of A for a feed rate of 0.5 liter/min. [16]
5. It is desired to produce 200 million pounds per year of ethylene glycol. The reactor
is to be operated isothermally. A one lbmole/ft3 solution of ethylene oxide in water
is feed to the reactor together with an equal volumetric solution of water contains
0.9 wt% of H2SO4. If 80% conversion is to be achieved, determine the necessary
reactor volume? How many 800 - gal reactors would be required if they are arranged
in series? [16]

6. The parallel decomposition of A, CAO = 2. as given in the gure 6.


Code No: R05310805
Set No. 1
Find the maximum expected CS for isothermal operations in a mixed ow reactor.
[16]

7. Starting with separate feeds of reactant A and B of given concentration, for the
competitive consecutive reactions with stoichiometry and rate as shown:

+ D esired

+ U nwanted

Sketch the contacting patterns for both continuous and non continuous operations.

(a) 1 = 1 A 2
[8]
B2=2RB

(b) 1 = 1 A B 2 = 2 R 2
[8]
B
8. For the elementary reaction system

298 = -14130
298 = -75 300 PA = P R = = 250 0

(a) Find space time needed for 60% conversion of a feed of AO=1000mol/min,
here AO=4mol/lit, using the optimum temperature progression in the Plug
Flow Reactor between00 C and 1000 C.
(b) Find the exit temperature of uid from the reactor [8+8]


Code No: R05310805
Set No. 2

1. Show that the following scheme
k1
25 2+* 3
k2
* - k3 + 2
*
3
*+* - k4 2
2
3
Proposed by R. Ogg, is consistent with, and can explain the observed rst order
decomposition of 2 5 [16]

2. (a) For the reaction A R, second order kinetics and A0 = 1 mol/liter, we get
50% conversion after 1 hour in a batch reactor. What will be the conversion
and concentration of A after 1 hour if A0=10 mol/liter?

(b) For the decomposition A R, A0 = 1 mol/liter, in a batch reactor conversion
is 75% after 1 hour, and is just complete after 2 hours. Find a rate equation
to represent these kinetics. [8+8]

3. Experimental studies of speci c decomposition of A in a batch reactor using pres-
sure units show exactly the same rate at two di erent temperatures:
At 400K -rA= 2 3p2
A
At 500K -rA= 2 3p2
A
Where - A = [ 3 ] and A= [atm]

(a) Evaluate the activation using these units.
(b) Transform the rate expressions into concentration units and then evaluate the
activation energy.
The pressure is not excessive, so the ideal gas law can be used. [4+12]

4. An aqueous reaction is being studied in a laboratory-size steady-state ow system.
The reactor is a ask whose contents (5 liters of uid) are well stirred and uniform
in composition. The stoichiometry of the reaction is A 2R, and reactant A is
introduced at a concentration of 1 mol/liter. Results of the experimental investi-
gation are summarized in the table. Find a rate expression for this reaction. [16]
Run Feed rate, Temperature Concentration of R
3/sec of run, 0C in e uent, mol/liter
1 2 13 1.8
2 15 13 1.5
3 15 84 1.8


Code No: R05310805
Set No. 2
5. A liquid reactant stream (1 mol/lit) passes through two mixed ow reactors in
series. The concentration of A in the exit of the rst reactor is 0.5mol/lit nd the
concentration in the exit of the second reactor.

(a) The reaction is rst order with respect to A and the volume ratio of reactors
2 1= 4.
(b) The reaction is zero order with respect to A and 1 2= 0.7. [8+8]

6. Consider the parallel decomposition of A of di erent orders as given in the gure6

Figure 6
Determine the maximum concentration of desired pro ductobtainable in:

(a) Plug ow reactor
(b) Mixed ow reactor, where S is the desired product and CAO =4. [8+8]

7. For the 1st order reactions k1 - k2
- taking place in a plug ow reactor
[16]
derive the expressions for Rm ax & Pop t

8. (a) Discuss about equilibrium conversions for exothermic and endothermic reac-
tions carried out adiabatically?
(b) Explain the procedure for obtaining the optimum feed temperature graphi-
cally? [8+8]


Code No: R05310805
Set No. 3

1. Show that the following scheme
k1
25 2+* 3
k2
* - k3 + 2
*
3
*+* - k4 2
2
3
Proposed by R. Ogg, is consistent with, and can explain the observed rst order
decomposition of 2 5 [16]

2. In the presence of a homogenous catalyst of given concentration, aqueous reactant
A is converted to product at the following rates, and A alone determines this rate:
A,mol/liter 1 2 4 6 7 9 12
- Amol/liter.hr 0.06 0.1 0.25 1.0 2.0 1.0 0.5
We plan to run this reaction in a batch reactor at the same catalyst concentration
as used in getting the above data. Find the time needed to lower the concentration
of A from A0 = 10 mol/liter to Af = 2 mol/liter. [16]

3. (a) A gas phase reaction 2A 3B + C is carried out in a variable volume batch
reactor. The reaction follows second order kinetics with reaction velocity
constant 0.05 3/kmol.s and initial concentration 0.05 kmol/ 3. Calculate
time required for 50% conversion of A.
(b) Explain the method of least squares and the method of excess for analysis of

4. A stream of pure gaseous reactant A ( A0 = 660 mmol/liter) enters a plug ow
reactor at a ow rate of A0 = 540 mmol/min and polymerizes there as follows: 3A
R, - A = 54 mmol liter. min . How large a reactor is needed to lower the concentration
of A in the exit stream to Af = 330 mmol/liter? [16]

5. It is desired to produce 200 million pounds per year of ethylene glycol. The reactor
is to be operated isothermally. A one lbmole/ft3 solution of ethylene oxide in water
is feed to the reactor together with an equal volumetric solution of water contains
0.9 wt% of 2 4. If 80% conversion is to be achieved, determine the necessary
reactor volume? How many 800 - gal reactors would be required if they are arranged
in parallel? [16]

6. Substance A in a liquid reacts to produce R and S as follows gure6:


Code No: R05310805
Set No. 3

Figure 6
A feed (CAO=1, CRO=0, CSO=0) enters two mixed ow reactors in series ( 1=2.5
min, 2=5 min). Knowing the composition in the rst reactor (CA1=0.4, CR1=0.4,
CS1=0.2), nd the composition leaving the second reactor. [16]

7. The liquid phase reaction of aniline with ethanol produces wanted mono ethylaniline
and unwanted diethylaniline.

- C6H5NHC2H5+H2O
C6H5NH2+C2H5OH k1 H2 SO4

- C6H5N(C2H5)2+H2O
C6H5NHC2H5+C2H5OH k2 H2 SO4

1 = 0 25 2

(a) An equimolar feed is introduced in to a batch reactor, and reaction is allowed
to proceed to completion. Find the concentration of reactants and products
at the end of the reaction? [8]
(b) Find the ratio of mono to diethylaniline produced in a MFR for an alcohol to
aniline feed ratio of 2 to 1 for 70% conversion of alcohol. [8]

8. Using optimum temperature progression in a mixed ow reactor for the reaction

between 00 C and 1000 C 298 = -75 300
298 = -14 130 P A = PR =
= 250 0

(a) Calculate the size of reactor is needed for 80% conversion when AO=4mol/lit,
AO=1000mol/min.
(b) What is the heat duty if feed enters at 25OC and product is to be withdrawn
at this temperature? P A is 250 cal/molA.K. [8+8]


Code No: R05310805
Set No. 4

1. Chemicals A, B, D combine to give R and S with stoichiometry A+B+D=R+S,
and after the reaction has proceeded to a signi cant extent, the observed rate is
R=ABDR

(a) What is the order of the reaction?
(b) The following two mechanisms involving formation of active intermediate have
been proposed to explain the observed kinetics
Mechanism-I:
A + B Y* +
+*
Mechanism-II:
A + D X* +
+*
Are the mechanisms consistent with the kinetic data?
(c) If neither is consistent, device a scheme that is consistent with the kinetics. If
only one is consistent, what line of investigation may strengthen the conviction
that the mechanism selected is correct? If both are consistent, how would you
be able to cho ose between them? [2+8+6]

2. (a) After 8 minutes in the batch reactor, reactant ( A0 =1mol/liter) is 80% con-
verted; after 18 minutes the conversion is 90%. Find a rate equation to repre-
sent this nd the rate equation to represent this reaction.
(b) Give a detailed account of autocatalytic reactions. [8+8]

3. (a) Find the rst order rate constant for the disappearance of A in the gas reac-
tion 2A R if, on holding the pressure constant, the volume of the reaction
mixture, starting with 80% A, decreases by 20% in 3 minutes.
(b) Explain the method of isolation and metho d of initial rates for the analysis of

4. An aqueous reaction is being studied in a laboratory-size steady-state ow system.
The reactor is a ask whose contents (5 liters of uid) are well stirred and uniform
in composition. The stoichiometry of the reaction is A 2R, and reactant A is
introduced at a concentration of 1 mol/liter. Results of the experimental investi-
gation are summarized in the table. Find a rate expression for this reaction. [16]


Code No: R05310805
Set No. 4
Run Feed rate, Temperature Concentration of R
3/sec of run, 0C in e uent, mol/liter
1 2 13 1.8
2 15 13 1.5
3 15 84 1.8

5. Substance A reacts according to elementary autocatalytic reaction A+R R+R,
k=4 lit/mol.min. We plan to processFAO =2 mol/min of a feed consisting of A
alone [CAO =2 mol/lit, CRO =0] to 99% conversion in a recycle reactor. Find the
recycle rate which will minimize the size of reactor needed and determine this size.
Compare this optimum size with a reactor with recycle ratio of in nity. [16]

6. Substance A in the liquid phase produces R and S by the following reactions as in
gure 6

Figure 6
The feed (CAO =1, CRO=0, CSO=0.3) enters two mixed ow reactors in series
( 1=2.5 min, 2=5 min ). Knowing the composition in the rst reactor (CA1=0.4,
CR1=0.2, CS1=0.7), nd the composition leaving the second reactor. [16]

7. Under appropriate conditions A decomposes as follows k1 - k2
- , where
1= 0.1/min, 2= 0.1/min. R is to be produced from 1000 lit/hr of feed in which
AO = 1 mol/lit, RO = SO = 0. What size of plug ow reactor will maximize
the concentration of R and what is that concentration in the e uent stream from
this reactor? [16]

8. Using optimum temperature progression in a mixed ow reactor for the reaction

between 00 C and 1000 C 298 = -75 300
298 = -14 130 P A = PR =
= 250 0

(a) Calculate the size of reactor is needed for 80% conversion when AO=4mol/lit,
AO=1000mol/min.
(b) What is the heat duty if feed enters at 25OC and product is to be withdrawn
at this temperature? P A is 250 cal/molA.K. [8+8]

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