Chemistry Reference
In-Depth Information
modes of operation: (a) In batch (B) polymerization all reactants were
added at once. (b) In monomer addition (M ADD), 10% of the monomer
was added to the precharge of all the other ingredients. The addition of the
remaining 90% of the monomer was started 5 min after the precharge was
added. Monomer addition was completed in 90 min. (c) In emulsion addi-
tion (E ADD), 10% of the monomer and 10% of the surfactant solution
were added in the precharge. The balance of the monomer and emulsifiers
was added in a time schedule like that for monomer addition.
B
100
80
60
40
20
0
15
30
45 60
Time (min)
75
90 105 120
Describe the differences you would expect in the molecular weight of
the polymer produced and in the particle size distribution. [
Hint:
From the
plot above it can be seen that the rate of monomer addition in cases (b)
and (c) was low enough that there was little unconverted monomer in the
system at any time. The rate of polymerization was evidently controlled
by the rate of addition of monomer rather than by the normal kinetics
described in Chapter 11.] Note from this example how changing the opera-
tion of the emulsion reaction with a fixed recipe is an effective way to
vary properties of polymers and latexes.
12-5
Consider an emulsion polymerization in a CSTR. The feed contains 6 mol
monomer per liter of liquid (monomer
water) phase. The initial volumes
of monomer and water have volume ratios of 2
/
1, and the ratio of the densi-
ties of polymer and monomers is 1.27. The reactor volume is 50 m
3
.The
rate of polymerization in interval II of the emulsion polymerization is 50%.
(a) What flow rate is required to produce an average conversion of 50%
in the reactor?
(b) What fraction of the exiting material is in the reactor for a time less than
the mean residence time? Assume a perfectly stirred isothermal CSTR.
1
12-6
Propylene can be polymerized in liquid monomer with a TiCl
3
/Al
(C
2
H
5
)
2
Cl catalyst. Typical pressures are about 400 psi, to keep propylene
in the liquid phase at 60
C. Catalyst is continuously fed to the reactor and
the slurry of polymer, which is at about 30
50% solids, is continuously
