Reactor Engineering (CEN 3002)
Problem Set 1
1. For the second order reaction, A+B C , what is the integrated rate expression when
the initial concentration of A, [A]0 is equal to the initial concentration of B, [B]0?
2. Determine the units of the rate constants (k’s) in the following rate expressions. Using
meters for length, moles for material quantity, grams for weight, and minutes for
time.
k [A]
a) -ra= k 1+[A]
2
b) -ra = k [A]2
k1 [A][B]
c) -ra = k
1+ 1 [B]
k2
3. The pyrolysis of acetaldehyde is proposed to follow the sequence of elementary steps
below. The radicals formed in the elementary steps can be considered to be reactive
intermediates.
𝑘𝑘1
CH3CHO → CH3* + CHO*
𝑘𝑘2
CH3* + CH3CHO → CH3* + CO + CH4
𝑘𝑘3
CHO* + CH3CHO → CH3* + 2CO + H2
𝑘𝑘4
2CH3* → C2H6
a) Express the overall reaction with the correct stoichiometry.
b) For each elementary step of the reaction, write a rate law expression. What are the
units of the rate constants?
c) Use the PSSH to derive an expression for the rate of disappearance of
acetaldehyde(-rAC). What are the units of your lumped kinetic constant?
d) Under what conditions would your rate expression, -rAC, reduce to:
-rAC = k C3/2AC , where k= k2 k10.5 k40.5
4. Consider an isothermal, continuous flow reactor where the following reaction occurs
in the liquid phase: 2A 3B + C. You are to design the reactor to have 95 %
conversion of A at steady state. The initial concentration of A is 10 mol L -1 and the
volumetric flow rate is constant at 7 L h-1. For the following assumed rate equations
(rA), calculate the reactor volume required for both a (i) CSTR and (ii) PFR:
a. -rA = k CA , where k= 0.9 h-1
b. -rA = k CA-2 , where k= 0.4 mol3 h-1 L-3
c. -rA = k , where k= 0.4 mol h-1 L-1
5. The gas-phase reaction shown below is to be carried out isothermally. The molar feed
is 50% H2 and 50% N2, at a pressure of 16.4 atm and 227 ⁰ C in a flow system.
1/2 N2 + 3/2 H2 NH3
a) Construct a complete stoichiometric table. Make sure to choose the
limiting reactant as the basis. Call the limiting reactant A, the other
reactant B, and the product C.
b) Calculate CA0 , δ, and ε. Determine the concentrations of reactant and
product when the conversion (as defined on the basis of the limiting
reactant) is 50%.
6. The production of methyl bromide is an irreversible liquid-phase reaction that follows
an elementary rate law. The reaction shown below, is carried out isothermally in a
semi-batch reactor (pictured)
CNBr + CH3NH2 CH3Br + NCNH2
(A) (B) (C) (D)
A solution of methylamine (B) in extra dry ethanol at a concentration of 0.025 mol
dm-3 is to be fed at a rate of 0.05 dm3 s-1 to a solution of bromide cyanide (A) in extra-
dry ethanol contained in a glass-lined reactor. The initial volume of fluid in the vat is
to be 5 dm3 with a bromine cyanide concentration of 0.05 mol dm-3. Assume that the
specific reaction rate constant is k = 2.2 dm3 mol-1 s-1 and the reaction can be
described with the elementary rate law. Use MATLAB to solve for and plot the
concentration of a) bromine cyanide and b) methyl bromide.
CB0 = 0.025 mol dm-3
VR0 = 5 dm3
v0 = 0.05 dm3 s-1
CA0 = 0.05 mol dm -3
