Chemical Reation Engineering Question Bank

 

1.        Determine the activation energy and the frequency factor from the following data for the bimolecular formation of methyl ethyl ether. 

2.         ToC          0     6     12    18    24    30
3.          
4.         10 k, 5.6   11.8  24.5  48.8  100   208

litres/gmol.sec

what do you understand by these two terms?

  1. The homogeneous gas-phase reaction A à 3B has a rate constant of k = 0.5 min-1. Obtain an expression for the total pressure in a constant volume reactor as a function of time t (min) and the initial pressure po. What will be the effect of 50% inerts present initially along with pure A?
  2. Under appropriate conditions, the following reaction takes place.

With k1 = k2 = 0.1 min-1. R is to be produced from 1000 litres/hour of feed with CAO = 1 gmol/litre and CRO = CSO = 0. What size of plug flow reactor will maximize the yield of R? What is the concentration of R in the effluent stream of this of this reactor?

  1. A reactor decomposing by a second order mechanism is passed through a PFR and CSTR of equal volumes in series. The effluent from the CSTR contains 1% of the original reactant. How much of the original reactant would be left in the process stream, if it passed through the CSTR and then through the PFR? There is no change in density or temperature of the process stream.
  2. Establish the kinetics of the thermal decomposition of Nitrous oxide from the following data and find the reaction rate at 990oC and an initial pressure of 200 mm Hg. 
9.         t, min                  20    53    100
10.     
% decomposition           23    50    73
  1. An elementary liquid phase reaction (irreversible first order) A à R, takes place in a PFR and the conversion is 96%. If a mixed flow reactor of 10 times as large as the PFR is hooked up in parallel with the existing unit, by what fraction could the production be increased for the same 96% conversion?
  2. Determine the activation energy and frequency factor using Arrhenius and Transition state theories from the following data: 
13.    k, min-1     0.001       0.05
T oC          0.0         100.0
  1. Sulfuryl chloride vapors are heated in a closed vessel for 45 min at 320oC and 1 atm initial pressure. The dissociation of SO2Cl2 to SO2 and Cl2 is a first order reaction. The reaction velocity constant is 0.00130 min-1. Calculate the percentage decomposition of SO2Cl2 and the time required to decompose 80% of SO2Cl2.
  2. A homogeneous liquid phase reaction A à R takes place with 50% conversion in a mixed reactor. The reaction is elementary second order.
    1. What will be the conversion if the original reactor is replaced by one which is six times as large as the original reactor - all else remaining unchanged?
    2. What will be the conversion if the original reactor is replaced by a plug flow reactor of equal size - all else remaining unchanged?
  3. A liquid is to be hydrolyzed in three mixed reactors connected in series. If each reactor has a volume of 2 litres and the feed rate to the first reactor is 500 cc/min, determine the percent hydrolysis accomplished in the three reactors.

Data: Rate of hydrolysis = r = 0.16 gmol/cc.min

  1. The thermal decomposition of nitrous oxide (N2O) in the gas phase at 1030oK is studied in a constant volume vessel at various initial pressures of N2O. The half-life data so obtained are as follows: 
18.    po (mm Hg)   52.5  139   290   360
t1/2 (sec)     860   470   255   212

2N2O à 2N2 + O2

Determine the rate equation that fits the data.

  1. The decomposition of NO2 follows a second order rate equation. Data at different temperatures are as follows: 
20.    T (K)       592   603   627   651.5 656
k (cm3/gmol.sec)522 755   1700  4020  5030

Compute the energy of activation E from the data. The reaction is 2NO2 à 2NO + O2

  1. Two stirred tanks of volume V1 and 2V1 are available for carrying out a first order irreversible reaction at constant density and temperature. If the flow rate of the feed stream is Q, which of the following arrangements would give the highest production rate of the product?
    1. Parallel operation of the two reactors, with equal average residence times.
    2. Parallel operation, with different average residence times.
    3. Series operation, with feed stream entering the larger reactor.
    4. Series operation, with feed entering the smaller reactor.
  2. The gas phase decomposition of A takes place according to the irreversible reaction, A à 3P. The kinetics of the reaction was studied by measuring the increase in pressure in a constant volume reaction vessel. At 504oC and an initial pressure of 312 mm Hg, the following data were obtained: 
23.          Time (Sec)  390   777   1195  3155  a
Total pressure (mm Hg) 408 488   562   779   931
    1. Test for a first order reaction.
    2. Calculate the value of the specific reaction rate at 504oC.
  1. The reaction A d B ‡ C has the rate equations.

rA = 0.4 CA, rB = 0.3 CB - 0.4 CC

Three tanks of different sizes are available. At the desired production rate, the residence times of 5 min, 10 min and 15 min, are maintained in the successive stages of the CSTR battery. The feed concentrations are CAo = 0.9 ; CBo = 1.2 and CCo = 0

Find the concentration of B in the effluent from each tank.

  1. Find the specific reaction rate and order of reaction for thermal decomposition of nitrous oxide on gold at 990oC and initial pressure of 200 mm Hg. 
26.    t, min      20    53    100
% decomposition     32&   50    73
  1. The decomposition of phosphine is irreversible and first order at 650oC.

4PH3(g) à P4(g) + 6H2(g)

The rate constant (sec-1) is reported as

log k = (-18993/T ) + 2 log T + 12.13

where T is in oK.

In a closed vessel (constant volume) initially containing phosphine at 1 atm pressure, what will be the pressure after 50, 100 and 500 sec. The temperature is maintained at 650oC.

  1. The kinetics of an aqueous phase decomposition of A is investigated in two CSTR's in series, the first having half the volume of the second. At steady state with a feed concentration of 4 gmol/lit., and mean residence time of 65 sec in the second reactor, the concentration of feed to second from the first is found to be 2 gmol/lit., while that of the stream leaving the second is 1 gmol/lit. Find the suitable kinetic rate expression.
  2. Two small samples of solids are introduced into a constant environment oven and kept there for 1 hour. Under these conditions 4 mm particles are 58% converted and 2 mm particles are 87.5% converted. Find
    1. the rate controlling mechanism for the conversion of solids.
    2. Time needed for the complete conversion of 1 mm particles in this oven.
  3. The catalytic reaction A Û M + N takes place in a reactor where the effect of diffusive mass transfer may be neglected. The following steps may be considered

                                 i.                         Adsorption of A

                                ii.                         Adsorbed A reacts with a vacant active centre to produce adsorbed M and N

                              iii.                         Desorption of M and N.

Assuming the surface reaction is rate controlling, develop the overall rate equation.

  1. The solid-catalyzed decomposition of gaseous A proceeds as follows:

A à R     -rA = kCA2

A tubular pilot plant reactor packed with 2 litres of catalyst is fed 2 m3/hr of pure A at 300oC and 20 atm. Conversion of reactant is 65%.

In a large plant, it is desired to treat 100 m3/hr of feed gases at 40 atm and 300oC containing 60% A and 40% inerts to obtain 85% conversion of A. Find the internal volume of the reactor required.

  1. A batch of solids of uniform size is treated by gas in a uniform environment. Solid is converted to give a non-flaking product according to the shrinking core model. Conversion is about 7/8 for a reaction time of one hour, and conversion is complete in two hours. What mechanism is rate controlling?
  2. The following kinetic data on the reaction A à R are obtained in an experimental packed bed reactor using various amounts of catalyst and a fixed feed rate of FAO = 10 kmol/hr. 
4.           W kg. catalyst 1       2       3       4       5
5.           6       7
6.           XA              0.12    0.2     0.27    0.33    0.37    0.41
0.44


Find the reaction rate at 40% conversion.

 

1.        Discuss the thermodynamic restrictions on the progress of reversible reactions.

  1. Develop an expression for the specific reaction rate constant based on activated complex theory.
  2. Distinguish between the methods available for establishing the kinetics of chemical reactions from the data obtained in a batch or continuous reactor.
  3. Compare the performances and merits of the plug flow and the stirred tank reactors behaving ideally.
  4. Derive expressions for the overall conversions for a reaction of known order.
  5. A homogeneous first order reaction is carried out in a batch reactor under adiabatic conditions. Develop a suitable method to find the relation temperature-conversion-time. State the assumptions made.
  6. Briefly explain the E and the F - curves. Draw the E and the F - curves for series and parallel combinations of one plug flow and one stirred tank reactors with unequal volumes. Comment.
  7. Differentiate between an elementary and a non-elementary reaction with suitable examples.
  8. What is understood by order of a chemical reaction? How is this different from "molecularity of the reaction", if a difference between the two exists.
  9. Discuss Arrhenius, Collision, and Transition state theories of temperature dependence of reaction rates.
  10. Derive an expression for the concentration in the N-th reactor, if N equal sized stirred tank reactors are assembled in series. Assume first order reaction.
  11. Discuss, how best you will arrange two unequal-sized stirred tank reactors for a given conversion and reaction order.
  12. Derive the relation between conversion and temperature for an adiabatic reactor using the energy balance and explain how you determine the reactor size for adiabatic operation of a plug flow and a stirred tank reactor.
  13. Discuss the principles of reactor stability and how it is established in a stirred tank reactor. Show qualitatively how endothermic reactions are always stable.
  14. Briefly discuss the models to explain the non-ideal behavior of tubular reactors. Describe one experiment to evaluate the parameters in any one of the models.
  15. What do you understand by "order of a reaction"? Indicate the methods available for determining the order of a given reaction.
  16. An elementary reaction A à R à S, takes place in a mixed flow reactor. Find the condition for maximum concentration of R. What is its value? (Assume no R and S initially)
  17. "There exists a conversion below which the performance of a mixed flow reactor is better or at least equal to that of plug flow reactor for adiabatic exothermic reaction" - Explain.
  18. Discuss briefly the shrinking core model used for describing the global rate of fluid-solid non-catalytic reactions, and outline design methods for such reactions.
  19. Explain the different models for gas-solid non-catalytic reactions of the type,

A(g) + bB(s) à E(g) + F(s)

  1. Discuss the differences between chemisorption and physical adsorption and their role in catalytic reactions.
  2. Discuss the effect of mass and heat transfer on the performance of industrial catalytic reactors.
  3. Compare the performance of fluidized-bed, trickle-bed and slurry reactors.
  4. 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 minimum when the reactors are equal in size.
  5. What is understood by 'optimum temperature progression'? Illustrate with an example of reversible exothermic reaction using a given feed material.
  6. Compare the performance of an adiabatic and an isothermal reactor, choosing an example of an exothermic reaction.

1.        Catalyst poisoning

  1. Adsorption isotherm
  2. Promoters and Inhibitors
  3. Auto-catalytic reactions
  4. Semi-batch reactors and utility
  5. Feasibility of reactions
  6. Stimulus - response technique to find RTD in reactors.
  7. Non-ideal flow patterns ins real reactor systems
  8. Zero order reactions
  9. Recycle reactors
  10. Theile modulus and effectiveness factor for porous catalysts
  11. Pore volume and pore size distribution in catalysts
  12. Optimum temperature progression
  13. Space time and holding time of flow reactors

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Last Updated: 03/10/03

 

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