Chemical Forums
Specialty Chemistry Forums => Chemical Engineering Forum => Topic started by: curiouscat on March 26, 2015, 03:21:00 AM
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What are ways to prevent foaming inside a vacuum evaporator? We get particularly bad foaming when a vacuum is applied. That causes colored entertainment into the normally clear condensate. If we try atmospheric evaporation the problem isn't as bad.
Any tips?
In terms of chemical anti-foaming agents what chemicals are worth a shot? The pH is alkaline. Dissolved organics in the system are ~1%.
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Years ago I used 1-octanol. But never tried it on large scale.
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Years ago I used 1-octanol. But never tried it on large scale.
Thanks! I will try that.
Right now I'm also tending towards silicones. Lot of alkaline waste-water applications seem to use silicones.
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Polydimethylsiloxane or simethicone are often used as anti-foamers in food & pharmaceuticals and are completely non-volatile (varying MWs) so will remain in your rotary flask. Not sure if you would rather the added defoamer go with your condensate but with enough vacuum & temperature 1-Octanol should be evaporated and collected in condensate (BP=195 C).
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Polydimethylsiloxane or simethicone are often used as anti-foamers in food & pharmaceuticals and are completely non-volatile (varying MWs) so will remain in your rotary flask. Not sure if you would rather the added defoamer go with your condensate but with enough vacuum & temperature 1-Octanol should be evaporated and collected in condensate (BP=195 C).
Either way is fine. I don't much care whether it ends up in condensate or bottoms so long as doseage isn't huge. i.e. ppm range.
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@disco
Do you happen to remember what dose you had needed? Approximately.
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The best antidefoamer is polydimethylsiloxane, hands down.
We use it for controlling the foam in dispersant agent so a lot of foam is expected, but with only a dosis of 0,5% v/v the product didn't present foam at all, so maybe you could try with your product a dose of 1ppm?
We sell it around the world for using it in a lot of different water types -including alkalines-.
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The best antidefoamer is polydimethylsiloxane, hands down.
We use it for controlling the foam in dispersant agent so a lot of foam is expected, but with only a dosis of 0,5% v/v the product didn't present foam at all, so maybe you could try with your product a dose of 1ppm?
We sell it around the world for using it in a lot of different water types -including alkalines-.
Thanks. 0.5% would be closer to 5000 ppm right?
Is PDMS heat stable? Our temperature is approx. 100 C with pH around 12.
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Thanks. 0.5% would be closer to 5000 ppm right?
I recommend making trials adding 1 ppm every time, till the moment you had no significant level of foam.
I was refering to the fact that even a product designed to disperse and make foam didn't make foam at all when you add 0,5%, so maybe your product (I don't know) would only require 1ppm?
Is PDMS heat stable? Our temperature is approx. 100 C with pH around 12.
My PDMS is presented in a really dilluted aquose emulsion solution, so the boiling point of the solution is ≈100ºC -I don't think it will have impact on your system if it's water-based-.
Sorry I don't have any idea about the PH effects.