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Author: Subject: Formaldehyde from plastic(report)
Hexabromobenzene
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[*] posted on 14-1-2022 at 18:09
Formaldehyde from plastic(report)


DANGER!!!Pyrolysis polyoxymethylene gives very high formaldehyde emission! Do not do it in home!
About 15 kilograms of plastic polyoxymethylene was pyrolysed in 4 times.
Pyrolysis setup is stell retort and water Double-step absorber. Absorber is simple container with water with a tube to the bottom of the vessel, which includes pyrolysis gases. Container are connected sequentially. First absorbers must be made of metal due to high gas temperature.
Volume of retort 12 liters. Loading plastic 4-6 kg. Volume of 1 absorber 5 liters. Second absorber 10 liter PE canister filled at half

Retort heated in furnace from steel barrel in which firewood burns.

Approximately 30 liters of formaldehyde concentration of about 12% were obtained. The resulting formaldehyde has a yellow-orange color and is contaminated by impurities of formaldehyde oligomer as paste like mass.

Formaldehyde was concentrated by freezing during frost -25C(cold winter). Liquid was separated from ice. About 10 liter formaldehyde with concentration about 30% was obtained. Formaldehyde and water have eutetic point -19.5 with concentration about 30%.

Conclusion: Pyrolysis polyoxymethylene gives low yield formaldehyde and resulting product is crude. It also dangerous. DO NOT INHALE smoke stands out during pyrolysis. Do not to be less than 10-20 meters from the leeward side from pyrolysis setup. Use gas mask to throw firewood into the furnace.

About 80%( More 10 kg) formaldehyde was emitted in atmosphere. Not more 30% formaldehyde was absorbed

Pyrolysis polyoxymethylene bad way to prepare formaldehyde. Hydrolysis in boiling sulfuric acid is more friendly. Pyrolysis of plastic gives too much stream formaldehyde which does not have time to dissolve in water . It also gives crude product


[Edited on 15-1-2022 by Hexabromobenzene]
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[*] posted on 15-1-2022 at 15:40


Quote: Originally posted by Hexabromobenzene  


About 80%( More 10 kg) formaldehyde was emitted in atmosphere. Not more 30% formaldehyde was absorbed

Pyrolysis polyoxymethylene bad way to prepare formaldehyde. Hydrolysis in boiling sulfuric acid is more friendly. Pyrolysis of plastic gives too much stream formaldehyde which does not have time to dissolve in water . It also gives crude product


[Edited on 15-1-2022 by Hexabromobenzene]


Why did you have this low yeald? Didn't you try to minimize emissions? I think your apparatus mightn't be efficient enough!!
What would the result of such a hydrolysis process be other than formaldehyde?
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[*] posted on 15-1-2022 at 22:30


I gave low yield because formaldehyde stream very high. I use 2 absorbers sequentially but it did not help. I can decrease formaldehyde stream if decrease heat. But pyrolysis will take many time up to 10-20 hours instead 1-2 hour. Also heat control is difficult if you use wood as fuel

Pyrolysis also produces some formaldehyde oligomer and dioxalane because it contains up to 1% ethoxy groups. Hydrolysis is more clean but i think it slowly
You can use boiling sulfuric acid 10-50% concentration

[Edited on 16-1-2022 by Hexabromobenzene]
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[*] posted on 30-1-2022 at 00:47


Have you also done this with sulfuric acid?
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[*] posted on 1-2-2022 at 13:11


I have no opportunity. But you can do it yourself.

POM plastic is difficult to crush. You will need bolt cutter, saw on metal, Pickaxe or heavy hammer. To protect against fragments, use a polycarbonate faceplate for the face
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[*] posted on 25-5-2022 at 03:29


I did another experiments with this plastic. The plastic was broken into pieces and 40% sulfuric acid was added for a week. No changes. Then the container with the plastic and acid was heated to 70 degrees. It began to smell of formaldehyde from her and irritates her nose strongly.

For hydrolysis of plastic, it must be boiled with sulfuric acid. Nothing happens at room temperature. I also stay plastic at 10% hydrochloric acid at 2 months. Also nothing happend

Or plastic can be pyrolysed as written above

[Edited on 25-5-2022 by Hexabromobenzene]
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[*] posted on 25-5-2022 at 07:32


I'm kind of surprised you're not trying to dissolve the polymer in a solvent, even weakly, before reaction. I'm guessing that the heat+acid reaction starts when the polymer softens. Going by the chart:

https://www.calpaclab.com/acetal-polyoxymethylene-chemical-c...

it appears that POM is severely degraded by GAA, which is also acidic, so might help depolymerization. Other solvents might include DMF, diphenyl ether, chlorobenzene, isopropyl acetate (but not ethyl?!), methylene chloride (but not chloroform), or limonene.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 25-5-2022 at 07:58


It makes no sense. The use of solvents is all the same as expensive as dichlormethane or DMF, in addition to a waste of solvent, leads to contamination of reaction products.
Solvents should be used only where necessary. Hydrolysis of plastic with sulfuric acid during boiling a pure process. Sulfuric acid is a cheap reagent that acts as a catalyst and can be used as many times

Before hydrolysis, plastic can be broken with a hammer or sledgehammer
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[*] posted on 25-5-2022 at 09:58


Quote:
The use of solvents is all the same as expensive as dichlormethane or DMF, in addition to a waste of solvent, leads to contamination of reaction products.

The solvent to try would obviously be acetic acid, which is around the same price as sulfuric acid, I just listed the others because I felt like it. The reason would be to lower the reaction temperature, which means that the gas stream will be cooler, and easier to condense/capture.




[Edited on 04-20-1969 by clearly_not_atara]
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