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Posted By: Atul Member Level: Diamond Posted Date: 01 May 2008
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2007 Anna University B.Tech Chemical engineering CH339 - CHEMICAL REACTION ENGINEERING - I Question paper
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ANNA UNIVERSITY :: CHENNAI – 600 025
MODEL QUESTION PAPER
VI - SEMESTER
B.TECH. CHEMICAL ENGINEERING
CH339 - CHEMICAL REACTION ENGINEERING - I
Time: 3hrs Max Marks: 100
Answer all Questions
PART – A (10 x 2 = 20 Marks)
1. Distinguish between elementary and non-elementary reactions.
2. A reaction has a stoichiometric equation A + B What is the order of the reaction.
3. A liquid decomposes by second order kinetics, and in a batch reactor 50% of A is converted in a 5-minute run. How much longer would it take to reach 75% conversion.
4. Define space time and space velocity.
5. Explain the graphical procedure for finding the composition in a series of unequal sized mixed reactors for which the space time’s are known.
6. Find the favourable contacting pattern to form R qualitatively for
7. What is the most general form of the energy conservation equation to what does it reduce to when applied to steady state reactors.
8. The pyrolysis of ethane proceeds with an activation energy of about 75,000 cal. How much is the decomposition at than at .
9. Define Heat of reaction, how is it calculated.
10. Using the integral method of analysis, obtain a relationship for determining ‘k’ for a first order irreversible reaction.
PART - B (5 x 16 = 80 marks)
11. Reagent A undergoes an essentially irreversible isomerization reaction that obeys first order kinetics A B. Both A and B are liquids at room temperature and both have extremely high boiling points. Determine the reactor volumes necessary to produce 2 million kgs of B in 7000 hours of operation if the reactor operates isothermally at 163 C what is the maximum heat that has to removed.
Data
Reaction rate expression r = kCA
Rate constant at 163 C = 0.8 hr-1
Activation energy = 28,960 cal/g mole
Heat of reaction = -83 cal/gm
Molecular weight = 250
CPA = CPB = 0.5 cal/g C
lA = lB = 0.9 gm/cc
Time for filling and draining = 10 and 12 min respectively
Time taken to heat the feed to 163 C = 14min (no reaction takes place in this time)
Conversion of A = 97% (16)
12.a)i) Determine the order of the reaction and the reaction rate constant for the thermal decomposition of nitrous oxide at 1030 K
Initial pressure of N2O (mm Hg) 82.5 139 296 360
Half-life (sec) 860 470 255 212 (8)
ii) The following additional data were reported at temperatures indicated.
Temperature K Initial Pressure (mm Hg) Half-life (sec)
1085 345 53
1030 360 212
967 294 1520
What is the activation energy for the reaction. (8)
(OR)
12.b) The aqueous reaction proceed as follows:
Time (min) 0 36 65 100 160
CA, mol/ht 0.1823 0.1453 0.1216 0.1025 0.0795 0.0494
with CAO = 0.1823 mol/lit, CRO = 0, CSO 5.5 mol/lit
Find the rate for this reaction. (16)
13.a) A homogeneous liquid phase reaction A R, -rA = k takes place with 50% conversion in a mixed reactor.
(i) What will be the conversion if this reactor is replaced by one 6 times as large – all else remaining unchanged. (8)
(ii) What will be the conversion if the original reactor is replaced by a plug flow reactor of equal size – all else remaining unchanged. (8)
(OR)
13.b) Consider the homogeneous isothermal gas phase decomposition of CH3CHO. . From experiments in a constant volume batch reactor a 791 k, it is known that the time required for 50% increase in total pressure is 197 sec. The initial pressure is 1atm. The reaction is known to be 2nd order in acetaldehyde. Determine the plug flow reactor volume necessary to process 120 lit/min of pure acetaldehyde to 80% conversion level. The feed pressure is 1atm. The reaction is irreversible. The pressure drop can be assumed to be negligible. (16)
14.a) A first order reaction is to be treated in a series of two mixed reactors. Show that the total volume of the two reactors is a minimum when the reactors are equal in size. (16)
(OR)
14.b) Substance A reacts according to the elementary autocatalytic reaction , k = 1 lit/mol min. We plan to process FAO = 1 mol/min of a feed consisting of A alone (CAO = 1 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. (16)
15.a) Consider the ammonia synthesis reaction being carried out at 450 C and 101.3 MPa . The feed stream consists of 60 mole percent hydrogen, 20% nitrogen and 20% argon. Calculate the composition of the exit gases, assuming equilibrium is achieved in the reactor. Make sure that you take derivations from the ideal gas law into account. The equilibrium constant expressed in terms of activities relative to standard states at 1 atm may be assumed to be equal to 8.75x10-3. The fugacity of pure H2 at 450 C and 101.3MPa may be assumed to be equal to 136.8 MPa (16)
(OR)
15.b) A and B react will each other as follows
Find what ratio of A and B should be maintained in a mixed flow reactor so as to maximize the fractional yield of the desired product S. (16)
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