BIO CHEMICAL ENGINEERING Question Papers (Supple, 2005)

SET : 1

1. The Elementary irreversible reaction 2A ® 2R + S is carried out in a Batch reactor at constant pressure pure ‘A’ is taken initially at a concentration of 1.33 mol/litre. The volume increases from 4–5 litres in the first ten minutes. Assuming ideal gas law to hold good. Evaluate the reaction rate constant?
2. In Fed Batch Culture operating with intermittent addition of glucose solution, values of the following parameters are given at t=2h, when the system is at quasi – steady state.
V = 1000 ml F= dv/dt =200 ml/h
S0= 100 g glucose/lit mMax = 0.3 h-1
Ks=0.1g glucose/lit
YMx/s=0.5 g dw cells/g glucose
a) Find initial volume of the Culture.
b) Determine the concentration of Growth limiting substrate in the Vessel at quasi steady state.
c) Determine the concentration and total amount of Biomass in the vessel at t=2h.

3. Explain the significance of PH stat ?

4. A Homogenous liquid phase reaction A®R -rA = K C
A2 takes place with 50% conversion in a mixed Reactor.
a) What will be the conversion if this reactor is replaced by one 6 times are large all else remaining unchanged?
b) What will be the conversion if the original reactor is replaced by a plug flow reactor of equal size all else remaining unchanged?

5. A reaction with following kinetics
rA = KCA where K = 0.0387 min-1 is to be carried out in each case of the following systems at an initial concentration of A as CAO = 1.3 g mol/litre and it is desired to obtain a conversion of 95%. Find residence times required.
a) For equal Distribution of feed stream into two perfectly mixed flow reactors in parallel.
b) For the perfectly mixed equal sized reactors in series.

6. The Reversible first order Gas reaction A 1R
2
is to be carried out in a mixed flow Reactor. For operations at 300 K, the volume of Reactor required is 100 liters for 60% conversion of A. What should be the volume of the reactor for
the same feed rate and conversion but with operations at 400 K?
Data K1 = 103 e-2415T
DCP = CPR-CPA =0
DHr = -8000 Cal/mol at 300K
K = 10 at 300 K
Feed consists of Pure ‘A’ total pressure stays constant

7. Describe the Non-ideal flow patterns that may exist in commercial reactors and outline a method for estimating residence time distribution in such reactors ?

8. Explain in detail the stiochiometry involved in the cell growth?

SET :2

1. a) Milk is pasteurized if it is heated at 630C for 30 min. But if it is heated to 740C, it only needs 15 sec, for the same result. Find the activation energy of the sterilization process?
b) Explain the effect of temperature on the chemical reaction?

2. Consider a 1000-litre CSTR in which Biomass is being produced with glucose as the substrate. The Microbial system follows a Monod relationship with mMax=0.4hr-1, Ks= 1.5 g/litre and the yield factor Yx/s=0.5 ggbiomass/g substrate
consumed. If Normal operation is with a sterile feed containing 10g/lit glucose at the rate of 100 lit/hr.
a) What is the specific Biomass production rate at steady state?
b) If Recycle is used with a recycle stream of 10lithr and a recycle biomass concentration five times as large as that in the reactor exit, what would be the new specific biomass production rate?
3. Explain the exponential feeding strategy with respect to synchronous growth and its application in product purification?
4. The Homogenous gas decomposition of phosphine 4PH3 (g) ® P4(g) + 6H2 proceeds at 12000K with first order rate
-r PH3 = 10
hr  CPH3
What size of plug flow reactor operating at 12000K and 4.5 atm can produce 80% conversion of feed consisting of 4 Kg.mol of Pure phosphine per hour?

5. Equimolar quantities of A, B and D are continuously fed to a mixed flow reactor. The elementary reactions that proceed in the reactor are as follows:
A + D K1 P ; B + D K2 Q
Given K1/K2 = 0.2, calculate the fraction of ‘P’ forced when
a) 50% of A is consumed and
b) 50% of D is consumed.

6. The thermal decomposition of Acetaldehyde CH3CHO(g) ® CH4(g)+CO(g) is studied in an ideal tubular flow reactor at a constant total pressure of Pt atm. Suppose pure acetaldehyde vapour enters the reactor at T0 K and a steady rate of F g/s. The Heat of reaction, specific heat of the reaction mixture can be assumed constant and equal to ΔH
Cal
g mol
and CP Cal/Gmol0C. The rate of reaction is given by the second order equation.
r = Ae−E/RT  PA
2 gmol/s cm3.
Where ‘E’ is the activation energy, in calories per mole and PA is the partial pressure of Acetaldehyde in atmospheres. If the reactor operates adiabatically, express the rate of reaction in terms of the conversion as the sole variable.

7. Develop an expression for external age distribution of N number of equal sized back mixed reactor in series assuming tank in series model holds good.

8. Explain specific growth with relevant equations?

SET : 3

1. The gas phase irreversible reaction (CH3)2O ® CH4 + H2 + CO was carried out in a constant volume batch reactor at 5040C. Show that the following data explains the I order kinetics and evaluate the rate constant. Initially products were not
present.
Time (sec) 390 777 1195 3155 ¥
PT (mm Hg) 408 488 562 799 931

2. In a two stage chemostat system, the volumes of the first and second reactors are V1=500 lit and V2=300 lit respectively. The first reactor is used for Biomass production and the second is for a secondary metabolite formation. The feed flow rate to the first reactor is F=100lit hr and the glucose concentration in the feed is S=5.0 g/lit.
use mMax=0.3 hr-1 Ks=0.1 g/lit Yx/s=0.4.
a) Determine cell and Glucose concentrations in the effluent of the first stage.
b) Assume that Growth is Negligible in the second stage and the specific rate of product formation is Qp=0.02 g p/g cell h and Yp/s=0.6g P/g s. Determine the product and substrate concentrations in the effluent of the second reactor.

3. Explain the significance of dissolved oxygen stat?

4. A Homogenous liquid phase reaction A®R -rA = K C A2 takes place with 50% conversion in a mixed Reactor.
c) What will be the conversion if this reactor is replaced by one 6 times are large all else remaining unchanged?
d) What will be the conversion if the original reactor is replaced by a plug flow reactor of equal size all else remaining unchanged?

5. A first order liquid phase reaction takes place in a mixed reactor with 92% conversion. The suggestion is to recycle a fraction of the product stream with no additional treatment. In what way it effects the conversion as long as the feed rate is not altered ?

6. Consider the irreversible constant density reaction sequence
A + B K2 C r2 = K2CACB
C K1 D r1 = K1CC
The rate constants are K2 = A2e−E2/RT
K1 = A1=e−E1/RT
Component ‘C’ is the desired product. The feed. Contains no C (or) D and
CA=CAO, CB=CAO
a) If an isothermal tubular reactor is employed, develop equations for calculating the conversion of A for which the yield of ‘C’ is maximum and for the constant temperature at which the reactor should operate to give the highest value of the maximum yield of C.
b) Develop equations for predicting the conversion of A for which the selectivity of ‘C’ with respect to ‘D’ is a maximum.

7. Determine the residence time distribution for an isothermal tubular-flow reactor in which the liquid is in laminar flow in an annulus of inner radius r1 and outer radius r2. Take a=r1/r2. the velocity in the Axial direction at any radius r is given by
u r = A[1− r
r2 2

1−α 2
ln 1
α  ln
r
r2 ]
Express residence time distribution in terms of mean residence time q.

8. Obtain the Rate equation describing the kinetics of an enzymatic reaction in a continuous stirred tank reactor by applying mass Balance?

SET :4

1. Data on the effect of temperature on the reaction between ethanol and acetic acid are reported below. Find out the values of the constants in the Arrhenious equation.
T0C : 30 40 50 60 70
K lit/gmol-hr : 0.5 1.1 2.2 4.0 6.0

2. a) What are the advantages of continuous Bioreactors over Batch Bioreactors?
b) If continuous Bioreactors have so many advantages over batch bioreactors, why they are not widely used in industry?

3. Explain the significance of dissolved oxygen stat?

4. Assuming a stiochiometry A ® R for a first order gas reaction, we calculate the size of plug flow reactor needed for a given duty (99% conversion of a pure A feed) to be V=32 liters. In that however the reaction stiochiometry is A®3R with this corrected stoichiometry, what is the required reactor volume?

5. A mixture consisting of 90 mole% A (45 mole/lits) and 10 mole% impurity B(5 mol/lit). To be of satisfactory quality the mole ratio of A to B in the mixture must be 100 – 1 (or) higher. D reacts with both A and B as follows.
A + D ® R -rA = 21CA CD

6. The vapour phase decomposition of phosphine, which is irreversible and first order, follows the reaction
4PH3gP4g6H2g
Pure phosphine is fed to a tubular flow reactor, operating at 1 atm and adiabatically with a feed temperature of 953 K. The reaction is endothermic, DHR = 23900 J/mol of phosphine at 250C. The molal heat capacities (J/mol K) are
P4(g) CP = 25.1 + 0.0040 T
PH3g CP = 28.0 + 0.027 T
H2(g) CP = 30.1
The Rate constant K, S-1 is the following function of temperature ln
K = -27.94 + 2 ln T – 43,672
What volume to molal feed ratio (V/F) would be required to obtain a conversion of 10% in one pass through the reactor ? What would be the conversion for the same V/F if the reactor operated isothermally at 953 K ?

7. A liquid phase reaction is currently carried out commercially in a series of three, equal volume stirred tank reactors operating isothermally. It is planned to replace these reactors with a single tubular flow reactor. To obtain the same conversion as in stirred tank equipment for the same Vt/Q; what degree of dispersion of Necessary in the tubular reactor. Determine the value of DL/UL, if the flow in the tubular reactor could be represented by dispersion model ?

8.a) Calculate the Dilution Rate required to reduce the substrate concentration from 20gm/lit to 5 gm/lit given Max = 1 hr-1 Ks=2gm/lit Yx/s=0.6 the feed is sterile?
b) A Micro organism is being continuously cultured in a chemostrat of volume 10 lit
and Monod model applies to the system with rx=0.5 gm/lit hr and Ks=gmlit Y, x/s = 0.8. A sterile feed enters the reactor at a substrate concentration of 50gmlit. What would be the substrate and Biomass concentration for a steady flow rate of 6 lit/hr?