plasticizers in nylon

[3800sc]

hello,

I am working as an engineering intern at a nylon production facility and am trying to determine how to capture caprolactam that is released from our pellets that are dried under heat and vacuum in a conical dryer.

The problem is that when it is released it moves into the vacuum lines causing clogs in the lines and over time makes its way into vacuum pumps and damages them.

The facility currently shuts down the entire drying system every three days or so and steams out the lines and dryers which is a considerable amount of down time as this takes at least 12 hours

Does anyone have any recomendations as to a trap or condensor that will work well to capture the monomer when it sublimes from a vapor to a solid

 

[patprimmer]

I thought it was water soluble, so a water based scrubber should remove it.

Regards
Pat
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[3800sc]

I was thinking along the same idea and both our chemical engineers here said we cannot put that in the line because moisture would migrate back to the drying chamber and increase drying times. Also at 29 inches of mercury vacuum the water would constantly boil off

 

[Demon3]

A cold trap should also work. They are commonly used to condense chemicals in vacuum systems.

Looks like this:

http://en.wikipedia.org/wiki/Cold_trap

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Demon3]

Also some vacuum pumps can be run in purge mode which lets the volatiles vents out of the hot oil and the pump runs. You don't get as low vacuum in that mode but it keeps the oil cleaner.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Compositepro]

There are several approaches you could take. A cold trap could work but it needs to be located right at your dryer to keep things out the piping. The better your vacuum, the better your drying, but the less effective the cold trap will be. You will collect things in your trap (like water as well as caprolactum) which will need to be removed frequently. Heat transfer in a vacuum is very poor.

Are you sure that you even need a vacuum? Stripping the pellets with a flow of hot air maybe all you need. That is standard practice at the extruder.

Since your are producing the nylon I would think that you would use steam stripping to remove all residual monomer and then dry the pellets. Perhaps your problem is with the steam stripper, if you have one.