„dry foam“ prevention in suspension polymerisation process...foam in the production of pvc 4...
TRANSCRIPT
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„Dry Foam“ Prevention in
Suspension Polymerisation
Process
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Polymerization processes
Emulsion Polymerization
Suspension Polymerization
Emulsifier:
• Sodium alkylsulfate
• Sodium alkylsulfonate
• Ammonium alkylcarboxy acid
• Sodium sulfosuccinate
•Dosage: ~ 1%
Suspension Aid:
• Polyvinylalcohol
• Methylhydroxycellulose
•Dosage: ~ 0,1%
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Foam in the Production of PVC
Polymerization
Reactor
Blowdown
Vessel
Monomer
Recovery
(VCM, water,
surfactants, etc.)
Storage
Tank
Str
ipp
ing
Co
lum
n
Points where foam may occure
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Production Problems caused by Foam
An increased foam build up
• reduces the space time yield of the reactor
• may increase fouling in the reactor which results
in higher maintenance and cleaning costs
• reduces the cooling capacity and may build up
layers on the cooling surface of reflux condensers
• may slow down the speed of demonomerisation
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Evonik Antifoams for PVC
Designed for E-PVC and Micro S-PVC:
-TEGO Antifoam KS 53
-TEGO Antifoam KS 95
Designed for S-PVC:
-TEGO Antifoam KE 600
-TEGO Antifoam 2280
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Sintered glass
To start, the cycliner is filled
with 1 l of surfactant solution
+ defoamer
Time is noted when foam
reaches 2 l mark
The Sintered Glass Test
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Test Results in Suspending Agent and
Emulsifier Solution
0.1% PVOH solution 1% DBS solution
TEGO Antifoam KS 53
TEGO Antifoam KS 95
TEGO Antifoam KE 600
TEGO Antifoam 2280
120 s
150 s
600 s
660 s
960 s
840 s
300 s
240 s
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Wet and Dry Foam
Wet foam Dry foam
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Gas Bubbles in Pure Liquids
When the bubble reaches the
surface it bursts immedeately
No stable foam can be build
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Foam Formation
Introduction and dispersion of
gas or air - formation of bubbles
Stabilisation by dissolved
amphiphilic molecules
Rising of stabilised bubbles
Penetration of the surface
formation of the double
layer
1
2
3
4
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Defoaming: Mechanism Theory
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Defoaming: Entering-Spreading
Entering - E
Spreading - S
Destabilisation
+ viscous drag on the
underlying liquid
E = g w/a + g w/o - g o/a > 0
S = g w/a - g w/o - g o/a > 0
wo
a
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Dry Foam in S-PVC
Bubble
PVC particles
Dry foam
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Standard Antifoams can not enter the
Surface
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TEGOPREN 5890
TEGOPREN 5890
• is based on organomodifies siloxane (OMS)
• is a 100 % product
• is selfdispersable. Dilutions are long term stable
• can be used in food contact application
(EU Regulation 10/2011)
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TEGOPREN 5890
TEGOPREN 5890 will be
added
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Tests with PVC Slurry
Glass pipe
To start, the cycliner is filled
with 1000 ml of PVC Slurry
Antifoam is added hwen the
foam reaches 1500 ml mark
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Test Results in Dry Foam
0
100
200
300
400
500
600
700
800
900
1000
0 5 10 15 20 25 30
ml fo
am
time (min)
TA KS 95
TA KS 53
TA KE 600
TA 2280
TP 5890