Spinning Disc Reactor for Green Processing and Synthesis - Process Intensification for Green Chemistry - page 78

UV intensity: 25 mW/cm 2
[PI]= 2% w/w
Disc temperature: 40°C
Disc diameter: 0.2 m
2.1 s

100

90

Range of tres: 0.2 -
Range of film thickness: 40- 210 microns

80

70

60

50

40

1 ml/s

30

20

5 ml/s

10

0

0 200 400 600 800 1000 1200

Disc speed (rpm)

Figure 3.18 Effect of disc rotational speed on the conversion of n-butyl acrylate in the SDR at
different feed flow rates. Reproduced from [ref 40] 2003 American Chemical Society.

#

polymerization but the shear forces developed within the film would promote excellent
mixing conditions.
N-butyl acrylate was chosen as the test monomer by which to evaluate the perfor-
mance of the SDR for photopolymerization [40]. With a propagation rate constant of

16 000 l/mol.s at 30 C and a temperature of polymerization of 77.4 kJ/mol, the bulk
polymerization of n-butyl acrylate presents significant challenges as a fast, highly
exothermic reaction system.
It was observed that the rate of photopolymerization in the SDR was extremely fast.
Conversions in excess of 90% were achieved in one SDR pass at 200 rpm disc rotational
speed, 1ml/s feed flow rate (giving a residence time of approximately 2 s) and a moderate
UV intensity of 25mW/cm 2 (Figure 3.18). It has been suggested that the high polymeri-
zation rates may be accounted for by the uncoiling of polymer chains subjected to the high
shear rates and radially directed centrifugal force on the rotating disc (Figure 3.19). This
effect would cause the chains to remain active for longer, thereby encouraging more
monomer molecules to be consumed [51]. Narrow MWDs of the polymer, inferred from
polydispersity indices (PDIs) in the range of 1.8-2.1, reflect the good temperature control
achieved in the SDR.

shear field

Entangled polymer coils Distentangled, extended polymer chains

Figure 3.19 Effect of shear on polymer coils Reproduced from [ref 52] by permission of
Oxford University Press, Inc 1999.

#