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2003 Course Chemical Reaction Eng. - II

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Total No. of Questions : 12] [Total No. of Pages : 4 P1490 [3764]-322 B.E. (Chemical Common to Biotechnology) CHEMICAL REACTION ENGINEERING - II (2003 Course) Time : 3 Hours] [Max. Marks : 100 Instructions to the candidates: 1) Answers to the two sections should be written in separate books. 2) Neat diagrams must be drawn wherever necessary. 3) Figures to the right indicate full marks. 4) Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. 5) Assume suitable data, if necessary. SECTION - I Q1) The reduction of iron ore of density B = 4.6 gm/cm3 and size R = 5 mm by hydrogen can be approximated by unreacted core model. 4H 2 + Fe3O 4 4H 2O + 3Fe With rate approximately proportional to the concentration of hydrogen in 24000 RT cm/sec . Taking D = 0.03cm2/ the gas stream. ks = 1.93 105 e e sec, calculate the time necessary for complete conversion of a particle from oxide to metal at 600 oC. Does any particular resistance control? If not what is the relative importance of various resistance? [18] OR Q2) A solid feed consisting of 20 % of 1 mm particles 30 % of 2 mm particles and 50 % of 4 mm particles is to be passed through a rotating tubular reactor, some what like a cement kiln, where it reacts with gas of uniform composition to give hard nonfriable solid product. Experiments show that the progress of conversion can reasonably represented by reaction control for unreacted core model and that the time for complete conversion of 4 mm particles is 4 hrs. Find the residence time needed in the tubular reactor for (a) 75% conversion of solids (b) 95% conversion of solids and (c) 100% conversion of solids. [18] P.T.O. Q3) The concentration of an undesirable impurity A in air is to be reduced from 0.1% to 0.02% by absorption in pure water. Find the height of tower required for counter current operations. All the data is in moles meters and hr. For packings : kAga= 32000 mol/hr.m3 atm kALa = 0.1/hr, HA=125 10 6 atm.m3/mol, L= L = 7 105 mol/hr.m2, G= G =1 105 mol/hrm2 at = 1 atm, molar density of liquid CT = 56,000 mol/m3.. [16] OR Q4) For the problem given in Q.3 replace the unreactive absorbent with reactive liquid which contains a high concentration of reactant B, CB1 = 800 mol/m3 (0.8N). A(g) +B(l) Product. The reaction takes place in the liquid and extremely rapid. Assume diffusivities of A and B in water are the same. kAl = kBl = kl. Determine height of column. [16] Q5) a) The chemisorption of hydrogen on copper is given as below at 25oC. What kind of isotherms fit these results. [8] H2 Pressure 1.05 2.95 5.40 10.65 21.5 45.1 95.8 204.8 mm Hg Vol. adsorbed cm3 at 0oC & 1 atm 0.239 0.564 0.659 0.800 0.995 1.160 1.300 1.471 b) Derive expression of effectiveness factor for cylindrical pore in a catalytic pellet with 1st order irreversible reaction. State the assumptions. [8] OR Q6) a) A gaseous reaction with a solid catalyst is carried out in a flow reactor. The system is isothermal, but it is believed that mass transfer resistance are important. (i) Would increasing the turbulance in the gas region next to the catalyst surface increase or decrease the global rate? (ii) If the system is not isothermal and reaction is exothermic would increasing the turbulance increase or decrease the global rate? [6] b) Describe determination of surface area by BET method. [6] c) Write short note on poisoning of catalyst. [4] [3764]-322 -2- SECTION - II Cat Q7) a) For the catalytic reaction A + B C derive the rate expression for the case of surface reaction as rate controlling step. [8] 1 1 1 Cl2 + H 2O with CuCl 2, KCl, b) For the reaction HCl + O 2 4 2 2 SnCl2 on silica catalyst, in differential and integral reactors. The rate of disappearance of HCl could be correlated by r= [ 1 ( K )C 4 K CHCl CO2 1 [1+ K 1 1 2 Cl2 CHCl + K 2 CCl2 1 2 CH ]2 2O ] Devise series of fundamental steps of adsorption and surface reaction which will give above rate expression. [10] OR Q8) a) For the catalytic reaction A + B C + D derive the rate expression for the case of adsorption of A is rate controlling step. [8] b) What is Thiele s modulus? When is mass transfer resistance is greater?[6] c) Explain preparation of Catalyst. [4] Q9) The liquid phase hydrogenation of -methyl styrene to cumene has been studied in a recycle batch reactor at 80 lb/in2 at s and 55oC. [16] H 2 (dissolved) + C6H5C(CH3 ) = CH2 (l) C6H5 CH(CH3 )2 (l ) The reactor was packed with 18 in Al2O3 spheres containing 0.5 at % palladium on the outer surface of catalyst. Data for two runs with different initial styrene concentration is follows. Run C4 Run C5 Moles of -methyl styrene t = 0 29.0 27.9 Moles of catalyst in reactor, 9 30.7 30.7 t, h Mole fraction cumene 0 0.0264 0.1866 4 0.0530 0.2114 8 0.0810 0.2332 10.5 0.0995 0.2552 17.5 0.1518 21.5 0.1866 [3764]-322 -3- For the integral changes in composition (during a run) shown, a plot of cumene mole fraction V/s time might be expected to be curved, yet the data show a linear relationship. What does this signify about the kinetics of the reaction? Calculate rates of hydrogenation from the data given. The solubility of hydrogen in the liquid is very low. OR Q10) The Catalytic reaction A 4R is studied in a plug flow reactor using various amounts of catalyst and 20 lit/hr of pure A feed at 3.2 atm and 117oC. The concentration of A in the effluent stream is recorded for the various runs as follows. Runs 1 2 3 4 5 Catalyst used, kg 0.02 0.04 0.08 0.12 0.16 CA,out , mol/liter 0.074 0.060 0.044 0.035 0.029 Find the rate for the reaction using differential and integral method of analysis. [16] Q11) The second order reaction A R is studied in a recycle reactor with very large recycle ratio and the following data are recorded: Void volume of the reactor: 1 liter, Weight of catalyst used : 3 gm, Feed to the reactor CA0 = 2 mol/liter, V0 = 1 liter/hr, CA, out = 0.5 mol/liter. Find the rate constant for this reaction. How much catalyst is needed in a packed bed reactor for 80% conversion of 1000 liter/hr of feed of concentration CA0 = 1 mol/liter. [16] OR Q12) a) Derive Michaelis-Menten kinetics. How the constansts Vm and Km are determined? [8] b) Discuss design of adiabatic reactor. rrr [3764]-322 -4- [8]

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