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Unformatted text preview: CE 561 Homework 12: Assigned 11/30/09, due 12/07/09
(1) Consider the reactions
(1) A + ½ B → C + 2 D, with r1 = k1CACB
(2) A + 2 B → E + 2 F, with r2 = k2CACB
(3) A + F → C + 3 D, with r3 = k3CACF
Where species C and D are desired products, while species E and F are undesired
byproducts. These reactions occur in an adiabatic CSTR at a constant density of 500
kg/m3. The feed stream contains species A and species B, in a 2 to 1 ratio (stoichiometric
ratio for reaction 1) in an inert solvent. The specific heat of the mixture is 2.5 kJ/(kg K).
Reaction (1) is slightly exothermic, with Hr,1 = -36 kJ/mol. Reaction (2) is highly
exothermic, with ∆ Hr,2 = -890 kJ/mol. Reaction (3) is endothermic, with Hr,3 = 206
kJ/mol. The rate constants are given by:
k1 = 2×105 exp( -80 kJ mol-1/(RT)) L mol-1 s-1
k2 = 1×1011exp(-200 kJ mol-1/(RT)) L mol-1 s-1
k3 = 2×1015exp(-220 kJ mol-1/(RT)) L mol-1 s-1
(a) For a fixed feed temperature of 810 K, and fixed residence time of 0.2 s, find and plot
the steady state temperature and species concentrations in the reactor for feed
concentrations of species A from CAo = 2 mol/L to CAo = 5 mol/L. Always keep the
feed concentration of B equal to half the feed concentration of A (CBo = ½ CAo). Plot
CAo on the horizontal axis. Plot the temperature or composition on the vertical axis.
(b) For a feed temperature of 810K, residence time of 0.2 s, and feed concentration CAo =
4 mol/L, analyze the stability of all possible steady states.
Note that this problem is a slight variation on problem 2 of HW 10, which many of you
were not able to complete. Having the solution to that problem in hand, I am hopeful
that you will have much greater success with this one. ...
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- Fall '09