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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“MumInn 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
ka
A2 + ZS ___>‘_" 2A.S
ka
1(4)
B + S .__.>‘ B.S
kb
kr
2A.S + BS .3— 2C.S + D.S
kr
kc
2C.S ._>"_‘ C2 + ZS
kc
kd
D.S 4:, D + 3
hi Assuming the surface reaction (3) as the ratelimiting 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 spacetime
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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 Fall '99
 Tsotsis

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