Chemistry Reference
In-Depth Information
60
50
40
30
20
10
0
0
100
200
300
400
500
600
700
800
r
Fig. 21 Simulation results for the Baker Williams column according to the molecular weight,
where the original polymer has a two dimensional distribution according (
16
)
is described using the Stockmayer distribution function (
15
), the operative condi-
tions are:
33
Z
¼
T
0
¼
480 K
D
T
¼
2
:
5
v
Max
¼
0
:
25
:
(71)
If the original copolymer is described by the distribution function given in (
16
),
the operative conditions are:
75
Z
¼
T
0
¼
400 K
D
T
¼
5
v
Max
¼
0
:
4
:
(72)
Figure
21
represents the simulation results for the BW run, where five fractions
are formed having an equal amount of the original polymer with a distribution
according (
16
). The obtained fractions show a clearly lower polydispersity than the
fractions obtained by successive fractionation methods. The maxima of the distri-
bution functions for the fractions are very close to the original distribution function.
This permits an accurate determination of the original distribution function. The
last fraction in Fig.
21
has a relative large nonuniformity. However, this can be
improved very easily by making more fractions from this material. One advantage
of the BW column is the possibility to vary the amount of polymer in the
corresponding fraction arbitrarily, without any limits given by the thermodynamics
or by the operative parameters of the column. R¨tzsch et al. [
50
] simulated the
fractionation of homopolymers having Schulz Flory distribution functions. They
could obtain fractions having a nonuniformity smaller then 0.01. This value could
not be reached if copolymers were considered. Usually, the nonuniformities lie
between 0.01 and 0.05 for copolymers.
In Fig.
22
, the fractionation effect of the BW method with respect to the
chemical composition is plotted for a copolymer having a distribution function
