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Che 442 Finals_Dec'02

# Che 442 Finals_Dec'02 - l ChE 442 Final Examination A...

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Unformatted text preview: l. ChE 442 Final Examination A ceramic tube is coated in the inside with a layer of catalyst and placed inside a differential CSTR reactor. The gas phase concentration of the feed stream is equal to CA1). A first order irreversible reaction takes place in the tube. E“Mum-Inn Develop the differential equation describing the phenomena of diffusion and the reaction inside the tube. ( Hint : Take the differential volume and write the mass balances. Consider diffusion only in the axial direction and reaction on the surface of the catalyst.) Define the Thiele Modulus and express the effectiveness factor as a function of the Thiele modulus. A first order reaction takes place inside a spherical catalyst particle. As a function of temperature the reaction rate behave as follows: A 5,3 (:09 B l/ T If for a given temperature in the region A the effectiveness factor is equal to 0.1, calculate the rate constant. The effective diffusivity at the same temperature is D6 = 0.1 cmz/sec and the particle size dp = 0.2 cm. 3. A single catalyst pellet 0.2 cm in diameter is suspended inside a differential ﬂow reactor. The concentration of the stream exiting the reactor is CAb = l mol/lit. The liquid velocity is 0.2 m/s, the kinematic viscosity is 10'6 m2/s and the liquid diffusivity is 10'9 mZ/s. If the porosity is a = 0.5, the tortuosity is 4 and the rate constant is 0.1 s'1 (for a ﬁrst order reaction), then calculate the overall effectiveness factor. Take constriction factor as 1. 4. The catalytic reaction A2 + B _> C2 + D obeys the following mechanism k-a A2 + ZS ___>‘_" 2A.S ka 1(4) B + S .__.>‘ B.S kb k-r 2A.S + BS .3— 2C.S + D.S kr kc 2C.S ._>"_‘ C2 + ZS k-c kd D.S 4:, D + 3 hi Assuming the surface reaction (3) as the rate-limiting step, derive the overall reaction rate expression. (1) (2) (3) (4) (5) 5. For the following rate expression kpCA 1 + kA.CA you are given the following rate data Estimate the values of kr and KA r4 6. A CSTR reactor operates at steady state at 2500C. A first order reaction occurs inside the reactor. The rate constant is 0.1 min'1 and the activation energy is 20 kcal/mol. The reactor space-time is 5 min‘. Suddenly the temperature controller malfunctions and the temperature is lowered to 2300C. Calculate the new conversion. How long will it take to reach within 70% of its new final conversion? f = k.CA The following reaction takes place inside an adiabatic flow reactor A _>B r = k( CA — CB/ke) Pure A is fed to the reactor at a temperature of 500C. The residence time in the reactor is long enough so that the reaction reaches equilibrium. Calculate the conversion and the exit _ temperature. Data: kc: 1.5 *104 @ T=25°C HA = -45 kcal/mol HB = -65 kcal/mol CPA = 60 cal/molK CpB = 60 cal/molK Reactor Volume V = 1000 lit Flow Rate of Pure A = 100 lit/min ...
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Che 442 Finals_Dec'02 - l ChE 442 Final Examination A...

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