GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-VII (NEW) EXAMINATION - WINTER 2018
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Subject Code: 2173514/2173509 Date: 26/11/2018
Subject Name: Environmental Reaction Engineering
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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MARKS
Q.1 (a) Define: 1) space time, 2) space velocity, 3) Recycle ratio 03
(b) Discuss size comparison of mixed flow reactor and plug flow 04 reactor for nth order reaction.
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(c) Derive the process design equation for mixed flow reactor. 07
Q.2 (a) Discuss advantages and disadvantages of batch reactor. 03
(b) Justify that CSTRs connected in parallel behave as one single 04 CSTR of the same total volume.
(c) In an isothermal batch reactor, the conversion of a liquid 07 reactant A is 70% in 13 minutes. Find the space time and space velocity necessary to effect this conversion in a plug flow reactor. Consider first order kinetics.
OR
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(c) A homogeneous liquid phase reaction with the stoichiometry 07 and the kinetics A? S, -rA = KCa2 takes place with 50% conversion in a MFR.
1) Find the conversion if this reactor is replaced by another MFR having volume 6 times that of the original reactor or other parameters remain same.
2) Find the conversion if the original reactor is replaced by plug flow reactor of the same size. All other parameters remain same.
Q.3 (a) Explain instantaneous fractional yield and overall fractional 03 yield.
(b) For following parallel reactions 04
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A?R
A?S
If R is the desired product and the order of reaction is same for both the reactions then how can one get more production of R?
(c) Prove that N number of same sized mixed flow reactors in series 07 can be approximated as a plug flow reactor.
OR
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Q.3 (a) The reactor setup consists of three plug flow reactors in two 03 parallel branches. Branch D has a reactor of volume 60 liters followed by a reactor of volume 40 liters. Branch E has a reactor of volume 50 liters. What fraction of the feed should go to branch D?
(b) For reactions in series
A?R?S
If R is the desired, which intermediate concentration should be used?
(c) Reactant A in liquid produces R and S by the following 07 reaction:
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A ? R
A ? S
Both these reactions are first order.
A feed with Cao =1, Cro = 0 and Cso = 0 enters in two mixed flow reactors in series (t1 = 2 min, t2 = 5 min). The composition in the first reactor is Ca1 = 0.40, Cr1 = 0.40 and Cs1 = 0.2. Find the composition leaving the second reactor.
Q.4 (a) Define mean residence time and variance with equation. 03
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(b) Explain pulse input experiment for RTD studies. 04
(c) The data given below represent a continuous response to a 07 pulse input into a closed vessel which is to be used as a chemical reactor. Calculate the mean residence time of fluid in the vessel and tabulate and construct the E curve.
| t, min | 0 | 5 | 10 | 15 | 20 | 25 | 30 | 35 |
|---|---|---|---|---|---|---|---|---|
| Cpulse | 0 | 1 | 5 | 8 | 10 | 8 | 6 | 4 |
OR
Q.4 (a) What are the causes of non-ideal flow in reactor? 03
(b) Explain relationship between E and F curve. 04
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(c) A sample of tracer hytane was injected as a pulse into a vessel 07 (to be used as a reactor) and the effluent concentration is measured as a function of time. The following data are obtained:
| t,min | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| C | 0 | 1 | 5 | 8 | 10 | 8 | 6 | 4 | 3 | 2.2 | 1.5 |
Construct the C and E curves and determine the fraction of material leaving the vessel that has spent between 3 and 6 min in the vessel.
Q.5 (a) Define: i) catalyst, ii) catalyst selectivity, iii) catalyst activity 03
(b) Differentiate between packed bed reactor and fluidized bed 04 reactor.
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(c) Write the sequence of steps according to shrinking core model for 07 gas-solid non-catalytic reactions. Draw a schematic figure to show these steps when reaction aA (g) + bB (s) ? products takes place on a solid spherical particle of unchanging size.
OR
Q.5 (a) Differentiate constant volume and variable volume batch 03 reactor.
(b) Explain types of catalyst deactivation. 04
(c) Qualitative discussion about product distribution in reactions in 07 parallel for two reactant.
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