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Posted By: acme Member Level: Silver Posted Date: 19 Apr 2008
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2007 Jawaharlal Nehru Technological University B.Tech Chemical engineering CHEMICAL REACTION ENGINEERING-II Question paper
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IV B.Tech I Semester Regular Examinations, November 2007
CHEMICAL REACTION ENGINEERING-II
(Chemical Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. Dispersed noncoalescing droplets (CAo= 2 mol/liter) react (A!R, -rA = KC2A
, k = 0.5 liter/mol. min) as they pass through a contactor. Find the average
concentration of A remaining in the droplets leaving the contactor if their RTD is
given by the curve in Figure 1. [16]
Figure 1
2. Consider a real tubular reactor in which dispersion is occurring.
(a) For small deviations from plug flow, show that the conversion for a first-orderreaction is given approximately as
X = 1 - exp [-kt +(kt )2/Pe ]
(b) Show that to achieve the same conversion, the relationship between the volume
of a plug-flow reactor VP and volume of a real rector V in which dispersion
occurs is
V/VP= 1 + kt [ D/UL] [8+8]
3. (a) Define the following terms:
i. Micro fluid
ii. Macro fluid
iii. Degree of segregation
iv. Earliness of mixing
(b) Explain the difference in behavior of micro fluids and macro fluids in mixed
flow reactor. [8+8]
4. In a non-catalytic fluid solid reaction the diffusion through Ash layer is the con-
trolling step. Derive the overall rate expression for the reaction of particles of
unchanging size. Express the conversion interms of reaction time. [16]
5. A 200 ton solid hold up is needed in a single fluidized bed reactor for 99% conversion
of particles of unchanging size where ash diffusion controls. What would be the
hold up in two fludized beds in series for indentical conversion, feed rate and gas
environment. [16]
6. Derive a rate equation for an instantaneous reaction of any order between A and
B, fluid-fluid reaction
A(gas) + bB(liquid) ! product
And sketch the concentration profiles assuming a two-film theory. [16]
7. The oxidation of ethylene to ethylene oxide is conducted in a fixed bed catalytic
reactor. The feed gas with a composition of 8% C2H4, 19% O2 and 73% N2 has
a superficial velocity of 60 cm/sec in the reactor, with silver catalyst, the intrinsic
reaction is given to r = 0.12 PC2 H4(Po2)0.2 K moles
hr. Kg catalyst
Two competing reactions occur in the reactor
C2H4 + 1/2 O2 ! C2H4O
C2H4 + 3O2 ! 2CO2 + 2H2O
The selectivity of ethylene oxide with respect to CO2 is independent of conver-
sion and is equal to 1.5. Calculate the minimum bed height required to achieve
20% conversion of ethylene to ethylene oxide. Density of catalyst particles = 0.04
gm/C.C. The reactor is operated isothermally at 280oC and 1 atm. pressure. [16]
8. The rate law for the hydrogenation (H) of Ethylene (E) to form ethane over a
catalyst is
-rE = k PE PH
1+KEPE
where in KE is equilibrium constant of the reaction and ? is rate constant of the
reaction.
Suggest a mechanism consistent with the rate law. [16]
? ? ? ? ?
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