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Nitrogen pipe used for reactor purging keeps clogging. Please help

Nitrogen pipe used for reactor purging keeps clogging. Please help

Nitrogen pipe used for reactor purging keeps clogging. Please help

Hello guys,

my name is Alex. I am currently working with two glass jacketed batch reactors - one 0.75 L and one 11 L. In those two reactors i am doing a simple step growth polymerization of polyethersulfones (substances used Bis A,DCDPS and K2CO3) consisting of two steps in NMP as a solvent at 190 degrees.

The reaction is done under inert atmosphere (nitrogen) for two reasons:
1. enables better removal of water and shifts the reaction to the product side
2. prevents side reactions with oxygen

The nitrogen pipe is inside of the liquid as by doing that the water removal outside of the reaction medium is better (especially when viscosity rises) and for better stirring of the medium.

Now to the problem:
In the first 2 hours of the reaction, the pipe gets constantly clogged with the substances because of the poor solubility of K2CO3 in NMP. In the beginning just small cloggings and after some time more and more, when eventually is totally blocked and i need to remove the pipe from the reactor, clean it and put it again inside of the reactor but this time above the reaction medium - at least for those two hours or so.

As explained earlier, it is not the best option to keep it above the r. medium and i don't know now what to do.
I tried pipes with smaller and bigger diameters, tried increasing the nitrogen-flow rate, then tried a pipe with small holes on the sides and the end being welded but nothing helps. To increase the temperature or change the recipe isn't an option.

I know there is probably a simple trick for that but i can't think of any. Could you guys help me and propose a couple of ideas?

Thank you very much in advance for your answers!
Replies continue below

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RE: Nitrogen pipe used for reactor purging keeps clogging. Please help

I cannot find it on the internet now, but I had a reactor with an injection quill that had a flush poppet valve at the tip. I believe it was Swagelok stainless 1/4" NPT on one end and on the other was a flat outer surface of the poppet. The poppet had a tapered sealing surface with an o-ring groove (shape similar to automotive engine intake/exhaust valves). It may have been called a check valve or a relief valve. A spring held the poppet closed with a 25 psi cracking pressure. It worked very well in not clogging and being easy to clean. It was used to inject a quenching liquid in case the thermoset resin being mixed went into an uncontrolled exotherm.

The closest I can now find with a similar function is this: https://saftflo.com/videos/saf-t-seal/

RE: Nitrogen pipe used for reactor purging keeps clogging. Please help

Dear Compositepro,

thank you very much for your answer! Sorry, me being a chemist, didn't quite understand half of the things you wrote. :D Do you maybe have pictures of that items that you used? I just looked at the link that you have sent. The problem could potentially for me lie in the types of rubbers used for the production of those tips - because first I have 190°C operating temperature for 10h and secondly, doing the reaction in NMP so i don't know if the rubber would stand long period of time undamaged.

Thank you very much for your answer!


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