Sathyabama University

Register Number SATHYABAMA UNIVERSITY (Established under section 3 of UGC Act,1956) Course & Branch :B.Tech - CHEM Title of the Paper :Chemical Reaction Engineering – IIMax. Marks:80 Sub. Code :619603/SCHX1032(2008/2009/2010) Time : 3 Hours Date :14/09/2013 Session :AN ______PART - A (10 x 2 = 20) Answer ALL the Questions 1. Define vessel dispersion number and peclet number

2. Derive relationship between E,C and F curve

3. Write limitations of shrinking core model.

4. A stream of particles of one size are 80% converted (SCM/ash diffusion control, uniform gas environment) on passing through a reactor. If the reactor is made twice the size but with the same gas environment, same feed rate, and same flow pattern of solids, what would be the conversion of solids if the solid flow is like Plug flow?

5. Write notes on catalyst preparation using gel permeation method.

6. Discuss Eley-Rideal mechanism

7. Define internal overall effectiveness factor

8. State the assumptions of Langmuir adsorption isotherm 9. Write the overall rate equation for the three phase reaction occurs in slurry reactor.

10. Write short notes on catalyst deactivation by coking.

PART – B (5 x 12 = 60) Answer ALL the Questions

11. Derive the dispersion model for tanks in series. (or) 12. A reactor with a number of dividing baffles is to be used to run the reaction A→R, with -rA = 0.05 CAmol/liter. min. (a) Find the E versus t curve.(b) Calculate the variance of the E curve. (c) Calculate XA directly from the data. Time, min 0 10 20 30 40 50 60 70

CA, mol/lit 35 38 40 40 39 37 36 35

13. For a gas- solid reaction, Fe3O4(s) +4H2(g) →3Fe(s) +4H2O(g). Develop the relationship between time, radius of the unreacted core and conversion ifdiffusion through ash layer and gas film controls, using UCM and state assumption. (or) 14. Spherical particles of zinc blende of size R = 1 mm are roasted in an 8% oxygen stream at 900°C and 1 atm. The stoichiometry of 2ZnS  3O  2ZnO  2SO the reaction is (s) 2( g ) 2 assuming that reaction proceeds by the shrinking-core model calculate the time needed for complete conversion of a particle and the relative resistance of ash layer diffusion during this operation. Data: Density of solid, p, = 4.13 gm/cm3 = 0.0425 mol/cm3 Reaction rate constant, k" = 2 cm/sec 2 For gases in the ZnO layer, De= 0.08 cm /sec Note that film resistance can safely be neglected as long as a growing ash layer is present.

15. Hydrogen is dissociatively adsorbed on the surface of the catalyst while toluene adsorbed on the catalyst. The reaction occurs between the two adsorbed sites and form the product of methane and benzene. Then the methane and benzene desorbed from the surface. If the desorption of benzene is the slowest step, then the derive the overall rate expression and mention the kinetic term, driving force, and adsorption term. (or) 16. (a) Comparison between physical adsorption and chemisorptions (b) Explain the mercury penetration method to find the pore size of the catalyst.

17. The First order reaction A→B was carried out over two different- sized pellets. The pellets were contained in the spinning basket reactor that was operated at sufficiently high rotation speeds the external mass transfer resistance was negligible. The results of two experiment runs were made under identical conditions are as given in below. (i) Estimate the Thiele modulus and effectiveness factor for each pellet. (ii) How small should the pellets to be made to virtually eliminate all internal diffusion resistance? Measured rate(obs) Pellet (mol/g cat .s) x 105 Radius(m) Run 1 15 0.022 Run 2 75 0.0022

(or) 18. Derive conversion expression for mass transfer limited reaction in packed beds. 19. Derive an expression for conversion as a function of time in case of irreversible second order reaction which is carried out isothermally in a batch reactor on a catalyst that is decaying as a result aging. Assume second order decay. (or) 20. Derive the design equation for the three phase fluidized bed reactor.