Dissolved oxygen removal from fluids (both inorganic and organic) 5

[lcms]

Dear Fellows,

Dissolved oxygen can be considered the most important poison of any REDOX polymerization initiation system. It reacts very rapidly with the reductor component of the REDOX system, deactivating it and suspending the reaction start until all the oxygen has been consumed (AKA "lag time" or "induction period"). It may take hours before the reaction begins even when there is only small amounts of oxygen present in one of the raw materials.

My first concern relies on the recycle Butadiene which, I suspect, has huge amounts of dissolved oxygen that enter through the low pressure section of my recovery system (leakages, as you may know well).

Therefore, I would kindly ask if there is anyone that have already used (or at least had already heard about) any kind of oxygen removal (chemical or mechanical) from this kind of product (hydrocarbons). So far I have studied two alternatives: - Nitrogen blanketing and membranes, but all of them presents some big disadvantages, as pressure build up (Nitrogen) or cost and clogging potential (membranes).

Thanks in advance,

Best Reagards,

LCMS.

 

[Latexman]

Icms,

You have much bigger concerns than a retarded or sluggish polymerization if oxygen gets in your BD. It's called peroxide formation and it's shock sensitive! This is why you want to inert with Nitrogen to raise the pressures so oxygen will NOT get in.

Good luck,
Latexman

 

[lcms]

First of all, thank you Latexman for your quick help.

By your answer I can clearly see that you are an experienced engineering in rubber polymerization (I have been working in this area as process engineering since ´86), and I fully agree with you. As a matter of fact, I can not understand well why we have not had any accident related to this problem so far (when I study this matter - Butadiene storage and handlind, mainly the subject of popcorn formation and peroxide - people allways warn about the major risks involved with these contaminants). Probably because we have been on a NALCO program that use an antipopcorn agent (NALCO 5222) and a strict cleaning popcorn routine (once a quarter we open all the equipment and remove all the solids - popcorn and peroxides - keep them in water until its final disposal - incineration). Even so, I desperataly need to install another system to remove the remaining oxygen, and you have already ranked a reason better than mine to making it. Do you, or any of our friends of eng-tips, have any experience with one of this systems? The way you referred to Nitrogen blanketing it seem to me it is a traditional approach (we do not use it yet, I am thinking about install one). Is it?

Looking forward to hear from you soon,

LCMS,

 

[Compositepro]

Butadiene and styrene require a free-radical inhibitor like tert-butyl catechol (ppm levels) to prevent the liquid from polymerizing in storage. Popcorn is polymerized resin and occurs in areas where monomer vapors tend to condense. The inhibitor is in the liquid phase and there in none in the vapor phase. Some level of oxygen is required for the inhibitor to work. Developing explosive levels of peroxide is not possble because peroxides are polymerization catalysts.

There are some very good handbooks on safe storage of these materials prepared by their manufacturers and they are on the internet if you search.

I think that the answer to your original question is that you should measure and control the oxygen and inhibitor level in your butadiene but it should not be zero. Nitrogen purging is used to prevent excess oxygen.

 

[Latexman]

Compositepro,

Tertiary butyl catechol (TBC) scavenges oxygen and free radicals, therefore it does not require oxygen to inhibit BD polymerization. Some monomer/inhibitor combinations do require oxygen for the inhibitor to be active, like an acrylate with MEHQ, but BD with TBC does not require oxygen.

Good luck,
Latexman

 

[Latexman]

LCMS,

Injecting inhibitors such as tertiary butyl catechol (TBC) and diethylhydroxylamine (DEHA) will scavenge oxygen and free radicals that are formed. There are some other proprietary inhibitors for oxygen and free radical scavenging sold by specialty chemical companies too.

However if you are looking at doing this as a result of an incident (runaway reaction), adding inhibitors to recyle BD will inhibit the polymerization too, so beware! If too much inhibitor is added, then the fix may cause another incident! Personally, I don't like this option.

Have you considered stripping the reactor charge with nitrogen prior to initiation?


Good luck,
Latexman

 

[Latexman]

Developing explosive levels of peroxide is not possble because peroxides are polymerization catalysts.

Besides just being wrong, this could lead someone to do an extremely unsafe act. I advise you follow your own advice and consult a BD manufacturer's literature, like Shell's PRODUCT STEWARDSHIP GUIDANCE MANUAL, which says "Butadiene and oxygen readily react to form thermally unstable butadiene peroxide. (The oxygen source can be either air or oxidizing agents.) Butadiene peroxides are extremely dangerous, particularly when concentrated and heated.

Butadiene peroxide is comprised of C4H6- and oxygen (-O-O-) units. This material is a viscous, oily liquid that is heavier (denser) than liquid butadiene. These peroxides are explosive, sensitive to heat and can initiate rapid polymerization. When concentrated, a fire or explosion can occur as a result of attaining a critical mass of these peroxides. Mechanical shock can also result in the explosive decomposition of these peroxides.

Peroxides are only slightly soluble in liquid butadiene, and can drop out and form a second liquid phase under the liquid butadiene. They have a solubility limit in butadiene in the range of 120-125 ppm but the solubility is dependent on the molecular weight of the peroxides. As the peroxides age, the molecular weight tends to increase and the solubility in butadiene tends to decrease. Also as they phase separate from the butadiene, the peroxides tend to accumulate in process low-spots since they are denser and only slightly soluble in the liquid butadiene. As a result, analysis of peroxides in the butadiene phase will not account for those peroxides that have already phase separated and collected in low spots in the storage/piping network."

Good luck,
Latexman

 

[lcms]

Latexman and Compositepro,

Both are right, I mean, I have already read some articles explaining the role of oxygen on TBC polymerization inhibition, and that is why we are strongly advised not to inject Nitrogen on liquid phase of styrene tanks storage in order to avoid complete oxygen depletion and deactivation of TBC (It is true, Latexman, I will look for this article on my material and send you a copy as soon as I can). On the other hand, you (Latexman) got exactly the point when have pointed out that the TBC presence would retard more my futher use (reaction) since I do not have a caustic wash system to remove it before reactor charge (I receive the pure Butadiene already washed - with 10 ppm of TBC content - from a closer suplier, and that is why I do not mix it with my recycled Butadiene as in any other else ordinary rubber manufacturer).

The approach I like most was Latexman to add EDTA (I did not remenber that could act so) or another oxygen scavenger designed not to interfere with its further use. Could you, please, name one or, at least, one suplier (NALCO?).

Thank you mates for all your valuable help.

Truly Yours,

LCMS

 

[ash9144]

Yes NALCO has a very good line of the amine inhibitors. I work at styrene plant and that is our supplier, it is more effective in Styrene than the tbc.

 

[Latexman]

LCMS,

Also try Mallinckrodt.

Styrene + TBC + oxygen is more effective than just styrene + TBC.

Butadiene + TBC is more effective than Butadiene + TBC + oxygen, and it's safer.

Good luck,
Latexman

 

[lcms]

Thank you all fellows for the help.

I sure will contact both companies (NALCO and MALINCKRODT) to select the most suitable oxigen scavenger for my aplication.

I hope one day I could help you as much you have helped me.

Regards,

LCMS.