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Author: Subject: Terephthalic acid from PET
chromium
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[*] posted on 12-12-2005 at 16:51
Terephthalic acid from PET


Terephthalic acid can be made by saponification of polyethylene terephthalate (PET). Polyethylene terephthalate is common polyester, readily available as plastic from drink bottles.

Saponification usually takes place if ester is heated with hydroxides. For example we could take NaOH solution in water and heat PET pieces in it. This however is less practical as takes hours or days to complete and product is harder to separate. It was possible to saponify thin pieces of PET at room temperature with month or less if solution of small amount of NaOH in 75% methanol was used. Saponification is trully fast if NaOH is dissolved in ethylene glycol and this solution is heated nearly to its boiling point (195...200C). Description of very similar process is given in [1].

C6H4(COOCH2)2 + 2NaOH = C6H4(COONa)2 + (CH2OH)2
192x + 80x = 210x + 62x

Reagents:
Ethylene glycol 55ml
NaOH 12.0g
PET 22.0g
sulfuric acid 5 mol/l solution 30ml

NaOH was taken with some excess over theoretical amount. Ethylene glycol is just solvent and does not take part in reaction. 55ml seemed fair amount for this reaction.

Mixture of ethylene glycol, PET and NaOH was well stirred in stainless steel beaker. Beaker was placed onto hotplate and heating applyed.

Hotplate was switched off as soon as mixture started to boil and was switched on again when boiling ceased. Boiling point of this mixture was near to 200C. Mixture was continuously stirred with steel rod. This process lasted 20 minutes. During this liquid turned milk-white and pieces of plastic gradually decomposed.

Beaker was removed from hotplate. After some cooling 200ml water was added and mixture was well stirred. More water was added and stirring was continued to dissolve all solid substance. Even though there were some white pieces that had inital shape of plastic parts it all dissolved. Almost 400ml water was needed for this. Solution was filtered with coffee filter.

5 mol/l sulfuric acid was added dropwise to filtered solution. White precipitate at once appeared. Ph was checked and no more sulfuric acid was added when ph 2 was reached. Adding of sulfuric acid must be done in well ventilated area as some dioxane may be involved. Testing of ph is not strictly necessary as amount of sulfuric acid can be easily computed. One needs 0.5 mole of sulfuric acid for each mole of NaOH initially taken. Mixture was well stirred and left to stand for 30 minutes.

White precipitate was separated at first by filtration. It still contained a lot of liquid that was impossible to remove this way. Impure and wet terephthalic acid was placed together with filter paper onto piece of strong cotton fabric. This fabric was folded as bag and pressed hard until no more water separated. This crude terphtalic acid was mixed again with 500ml water and separated by filtration and pressing to get still purer product.

Yield of terephthalic acid is almost theoretical. Ethylene glycol can be concentrated from aqueous solution by boiling and used repeatedly. Concentrating must be done in fume hood as some dioxane may be formed because of sulfuric acid.

Terephthalic acid is almost insoluble in water. When clean it is odorless. It is not deliquescent but somewhat hygroscopic. Heating is needed to dry it completely and remove last traces of organic solvents.

References:

1. A. Oku *, L.-C. Hu, E. Yamada, "Alkali decomposition of poly(ethylene terephthalate) with sodium hydroxide in nonaqueous ethylene glycol: A study on recycling of terephthalic acid and ethylene glycol", J. Appl. Polym. Sci. 1997,. 63, 595



[Edited on 13-12-2005 by chromium]

[Edited on 13-12-2005 by chromium]

[Edited on 13-12-2005 by chromium]

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Polverone
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[*] posted on 12-12-2005 at 23:22


Interesting, Chromium. I will turn this into a PDF. It is possible to do the same in a strong aqueous solution, though. With enough NaOH the temperature can be raised well above 100 C without boiling. Overnight heating seems sufficient to decompose plastic this way. I noticed the same phenomenon where the plastic stays in chunks even though it turns white and dissolves easily when more solvent is added.



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chromium
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[*] posted on 13-12-2005 at 00:27


I did this once in aqueous solution but problrem was that PET started to decompose with reasonable rate if near-boiling NaOH solution was almost concentrated. Lot of NaOH is needed for this and such solution corrodes even stainless steel, although verry slowly. I had no idea how to separate sodium terephthalate or terephthalic acid from concentrated NaOH solution without reacting lot of NaOH with acid. So i looked for better way.

[Edited on 13-12-2005 by chromium]
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[*] posted on 13-12-2005 at 12:00


.....in aqueous solution but problrem was that PET started to decompose .........

Were you able to identify the decomposition products? or
Venture a quess perhaps?

Seems that benzoic acid as from pyrolysis of PET would be formed also here to some extent if decomposed.
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chromium
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[*] posted on 13-12-2005 at 12:13


Quote:
Originally posted by bio2
.....in aqueous solution but problrem was that PET started to decompose .........

Were you able to identify the decomposition products? or
Venture a quess perhaps?

Seems that benzoic acid as from pyrolysis of PET would be formed also here to some extent if decomposed.


No-no this decomp was just saponification as with ethylene glycol.
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[*] posted on 13-12-2005 at 15:20


FYI, the industrial deesterification process involves high-temperature water or ethylene glycol in an autoclave. I forget typical processing times.

Tim




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[*] posted on 13-12-2005 at 16:00


Here is an interesting article on the subject.


http://www.mhi.co.jp/tech/pdf/e401ex/e395254.pdf
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[*] posted on 14-12-2005 at 14:48


I have made a PDF version of your article. It can be found at http://www.sciencemadness.org/member_publications/terephthal.... Once it has been looked over it will be added to the article index like the others were. I made a small addition to the article: I included a picture of the recycling symbol that indicates an article is made of PET. I do not know if this symbol is used worldwide or just in the US. If non-US members inform me that it is unfamiliar, I will add a note that it is not an international symbol.



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[*] posted on 14-12-2005 at 16:32


I was wondering why a mad scientist would want terephthalic acid.
It doesn't seem all that useful to me.
Would it be terribly interesting to make polyester at home? Certainly the aim is not PET if that is the starting material.

What are some of the mad uses for it in the amateur world?
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[*] posted on 15-12-2005 at 05:51


Well, I can think of two uses for TPA.

1. Potassium hydrogen terephthalate makes very nice pyrotechnic whistles (with KP oxidizer) and has the advantage of being just about completely non-hygroscopic.

2. If you can decarboxylate benzoic acid to benzene, you should be able to do the same with TPA. It will of course require twice as much alkali.
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smile.gif posted on 14-4-2006 at 17:27
From my notebook


Three 500mL PET bottles were cut up into ~1cm.sq bits and massed to 22.0grams. The greenish(dyed) impure ethylene glycol was placed in a 250mL flask and heated with mag. stirring. 12 grams NaOH was added and white fuming and foaming was seen. The color changed to a light orange tint. Then the plastic bits were added slowly. The flask had to be removed for a bit many times to prevent foam from spilling over but despite this the addition was easy. Then 500mL d-H<sub>2</sub>O was added to get the mass out and was poured into a beaker and stirred then filtered. 30% sulfuric acid was added slowly to produce a milky white precipitate and this was stopped once the pH was ~2. The precipitate was filtered with a cotton shirt and some was lost due to mechanical errors. This was then washed with more water and refiltered. Then it was placed in a glass dish and dried at low heat in the oven.

I only got 6.8 grams total and this seems to be a shitty yeild so I may try again some time. I also wonder if DMSO would work as the solvent.




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chromium
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[*] posted on 15-4-2006 at 05:08


Maybe more time and mixing when terephtahlaic acid is precipitated?

I do not know if this is related to your results but i did notice only very litle foaming when NaOH was added.

I did this in stainless steel vessel because NaOH at nearly 200C can probably dissolve glass.

[Edited on 15-4-2006 by chromium]
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[*] posted on 17-6-2006 at 18:01


Quote:
Originally posted by Quantum
I only got 6.8 grams total and this seems to be a shitty yeild so I may try again some time. I also wonder if DMSO would work as the solvent.


Quantum it has been awhile since this post. By any chance have you tried DMSO instead. I am having issues finding pure Ethylene Glycol but I can acquire DMSO no problem.


DMSO's boiling point is ~189 Celcius (wiki as source). hmmm 11c short. I'll give this a shot anywho. I just hope no DMSO/NaOH gets on me:o.

[Edited on 18-6-2006 by DeAdFX]
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[*] posted on 4-8-2006 at 13:19


Quote:
Originally posted by DeAdFX
DMSO's boiling point is ~189 Celcius (wiki as source). hmmm 11c short. I'll give this a shot anywho. I just hope no DMSO/NaOH gets on me:o.


It's also been awhile since you last posted DeAdFX, I was wondering what the results were using DMSO as the solvent?

I'm just curious, as I bought some DMSO (for another purpose, actually) and remembered that you were going to try using DMSO as the solvent.
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[*] posted on 25-11-2006 at 15:36


My Hero!

Some time ago I started compulsivly collecting PET, in the theory that it is more valuable or will become more valuable then say aluminium scap. Its a speciality chemical. I have 1000 projects on the shelf but but your refining the goods.


I hope this will inspire me to buy a grinder and go threw the 15 garbage bags that are now in my way.

Why PET?!!!! Try buying a 50 foot+ square PET tarp. Not the weave stuff, a mono film tarp. Only NASA has them, prove me worng so i can buy one.

An inflatable dome that is PVC will run you $4000+ (china inflatable)

Ok so work with me on how to get a tarp.

I want to dissolve the TPA in toulene(tobedetermined) and let the film spread out over a pond of water ( inside or whatever) then the linker (ethylene glycol) with acid or base catylst shall be sprayed in a fine mist causing the film to polymerize. If it was clear that would be nice and preferable. For use with greenhouses or personal blimps.

The other option is making or purchasing( i'd rather just collect it for free) PET rolls of any thickness and up to 8 foot across http://petfilm.com/

then ironing/glueing them together

Time time precious time..... i cant bloody do half of it

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[*] posted on 9-1-2007 at 17:27


Awesome synthesis, very OTC!

Is it possible to prepare phthalic anhydride from terephthalic acid?

I would like to use it in making Fluorescein

thanks,

Mericad
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[*] posted on 9-1-2007 at 20:00


I don't think terephthalic acid can be converted to phthalic anhydride, at least by any simple means. I read that phthalic acid dehydrates at 210C to the anhydride. Phthalic acid can (supposedly) be made by oxidizing napthalene, available as mothballs, using chromate or permanganate.



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[*] posted on 9-1-2007 at 21:54


Quote:
Originally posted by mericad193724
Awesome synthesis, very OTC!

Is it possible to prepare phthalic anhydride from terephthalic acid?

I would like to use it in making Fluorescein

thanks,

Mericad


No, this isn't possible. YOu'd have to change the entire ring-connectivity to achieve that.

Since an intramolecular anhydride of terephtalic acid cant exist (the benzene ring is not flexible, thus the distance between the carbonyls at 1 and 4 positions cant be bridged), I wonder whether an *inter*molecular anhydride of terephtalic acid can be prepared? This would be a polymer essentially. What happens upon excessive heating of terephtalic acid?




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[*] posted on 9-1-2007 at 22:14


I'm pretty sure TPA sublimes when heated enough. The oxidation of napthalene seems workable I think. You would probably produce a mix of the isomers though (I know next-to-squat about organic chem) Use alcohol to remove the meta and ortho forms and leave behind the terephthalic acid. Heat the mix to 284C so pure phthalic anhydride vaporizes out of the mix and condense it (somehow). I suppose an alcohol wash would take any solid off the equipment afterward.



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[*] posted on 21-12-2008 at 08:56


I have made two batches of TPA from PET bottles.
The only problem i have faced however is the drying of the TPA.
I find however many times i wash the crystals with cold water ( i did it about 7 times) there is always some remainding ethylene glycol which makes it extremly difficult to dry the crystals.
I have tryed squeezing it close to dry between cloth but it does nothing but loose precious TPA and its only removes a bit of the water/ethylene glycol.
Has anyone else had this problem and how did they sort it?
thanks
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[*] posted on 21-12-2008 at 10:41


Picric- Why not dissolve in sodium hydroxide solution, dilute to several times the original volume, and acidify. It wont dry it out for you, but it'll get rid of the ethylene glycol. Can it be recrystallized directly from methanol or iPrOH?

[Edited on 12-21-08 by UnintentionalChaos]




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[*] posted on 21-12-2008 at 11:30


I viewed the crystals under a microscope and they look like little sponges, no wonder they shrink to about 1/5th of their volume upon drying :P
UnintentionalChaos - Yes the dissolving in NaOH soloution workes but it takes longer, more acid and more alkali, so not really worth it.
I was looking for a way to try change their crystal structure, but i doubt there is a way. If anybody know anything that may help i think it would start an usefull conversation.
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[*] posted on 21-12-2008 at 17:40


Drop the crude TPA in about 20 ml of water per gram of TPA, add a few drops of concentrated hydrochloric acid. Heat until on the edge of boiling, stirring well for at least 5 minutes and longer if it's easy. Let slowly cool, then chill if practical, filter.

Prolonged boiling seems to give a bit denser product, and gives the glycol a chance to diffuse out into solution. The added acid is to insure no alkali salts of TPA are left. The TPA does retain the solution, a second treatment omitting the HCl should reduce the amount of glycol and mineral acids quite low.
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[*] posted on 10-1-2009 at 17:35


If I'm correct PET is made by the reaction of terephthalic acid and ethylene glycol. Why doesn't the TPA react with the ethylene glycol solvent to form PET?



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[*] posted on 10-1-2009 at 18:35


You're essentially driving the esterification equilibrium (Le Chatelier''s, remember?) towards acid+alcohol instead of the ester. Also, a saponification like what chromium described is not likely to go backwards.

sparky (~_~)




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