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]

From my notebook

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.

[Edited on 18-6-2006 by DeAdFX]

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.

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
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.

Anhydrous oxalic acid? Obtained from an aqueous alkaline solution? Picric-A I think you might have some wires crossed lol! Really it seems a bit "idealistic green chemistry" kind of themed. You could always obtain your chemicals through your usual methods...

Quote: Originally posted by Paddywhacker

Edit:- The product was dispersed in 200 ml of boiling EtOH which was then chilled in the freezer and the slurry refiltered on buchner. The product, after drying for 8 hours in a vacuum, weightd 20.85 g. This is a yield of 110%. I wonder if there isn't some mono ethylene glycol ester of terephthalic acid in the product. [Edited on 3-3-2009 by Paddywhacker] [Edited on 4-3-2009 by Paddywhacker]

Hey, guys, let's not be too harsh. It may not be accessible to most amateurs, but it's something to read. Thanks, Picric-A.

Attachment: ie010563z.pdf (94kB)
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[Edited on 6/29/09 by bfesser]

I have a large beaker of disodium terephthalate solution awaiting further purification at the moment. I don't have my notes with me, but I'll add in some details later when I have a yield.

I used diethylene glycol as solvent with dry NaOH prills in 25% excess of theoretical. Approximately 100mL of DEG, 25g NaOH (.625mol), and 48g of PET (0.25mol) were used. Depolymerization proceeded smoothly with heating in a stainless steel reaction vessel under constant stirring. There was constant evaporation of ethylene glycol from the reaction mix while heating for 20 minutes.The resultant off-white slurry dissolved in 400mL of water and about 4g of PET had not reacted after becoming encased in disodium terephthalate. Either longer heating or more vigorous stirring is required.

90g of 92% NaHSO4 dissolved in about 200mL of water was used to precipitate the free acid from solution as flocculent, white material. This was collected by vacuum filtration and redissolved in 22.62g of NaOH and an arbitrary amount of water (@400mL). I will reacidify and boil to form a more compact precipitate later on.

The diethylene glycol was from this product, which is sold as a chafing dish fuel:



http://www.candlefuel.com/pdf/CLC_Deg.pdf

As the MSDS shows, the only ingredient is DEG, without any dyes or water. I found that each can yields about 235mL, but needs filtration through real filter paper to remove stray fibers from the wick material. Coffee filter allows short pieces of the material through and it's too viscous to pass through cotton. Of course, if you filter the mixture after the heating, this isn't necessary, but I mean this more for other reactions.

Purchased locally, each can costs me $1. It'd be a waste of my time to boil the waste down unless I was doing this on a massive scale, since less than half a can (100mL) is enough solvent to handle 0.25mol of shredded PET.

Update: Okay, someone else who's done this, take a small sample and heat it intensely, like on the surface of a hotplate. Does it char or leave black residue?

The reason beaing that I was drying some of my product with heat last night (very high sublimation point, so why not crank it up?) and noticed a good deal of charring on the bottom of the evaporating dish.

So, I ramped up the heat until I got white fumes and no more water was condensing on a watch glass, moved the sample to a crystallizing dish, and sublimated it under atmosphere.

I got pale yellow, fluffy crystals. A small spatula, placed directly on the ceramic of my hotplate sublimated without residue when heated strongly.

I'm not exactly happy about whatever the yellow is, but I've eliminated whatever was charring.

[Edited on 7-2-09 by UnintentionalChaos]

Copper salt

I prepared 16 Moles of Terephthalic acid by saponification with KOH in PG and then percipitate the TA with dilute H2SO4.

The TA was then washed with H2O and filtered a few times.

The Ta was then made in to its water soluble diamonium salt by a slight exes of ammonia.

The di amonium salt solution was left in a shed for some months to let the exes ammonia evaporate and the contaminant to aglomerate to some extent.

I suspect Bismuth used at about 2% as a catalyst in the polymerisation of TA to PET to constitute the colored contaminant. A 20 liter bucket of the crude di ammonium solution locks similar to tea in the color.

I then purified activated coal (Norit) by boiling in water so remove salts and other impurities as well as increasing its activity a few 100%

Repeated filtration with the purified activated coal made the solution clear.

I then purified an slight molar exes amount of copper sulfate solution by filtration with some purified activated charcol to eliminate insoluble (copperoxycloride and possibly som copperoxide?) and other cotaminating components.

The resulting clear blue solution was combined with the di ammonium terephthalic acid to percipitate a skye blue coppersalt of terephthalic acid.

Repeated washings and filtration trough a peace of cotton eliminated the soluble ammonium sulphate generated by the reaction. washings was repeated until the exes blue copper sulfate was no longer visible in the removed water.

(The particles are extremely small so filtration is rely a bitch!)

A half year after i started this i have quite a bit of a very pure non hygroscopic i insoluble copper salt with all its possible uses

Thanks for posting the info that made me realize i needed to do this

"TurboSnail"
>>>_@/"

Quote: Originally posted by UnintentionalChaos

Phthalic acid can (supposedly) be made by oxidizing napthalene, available as mothballs, using chromate or permanganate.

Quote: Originally posted by Waffles SS

What will be made if we use PP(Poly Propylene) instead of PET(Poly Ethylene)?

Nothing! Wrong reading !
*PET is Polyethyleneterephtalate thus a polyester ((-CH2-CH2-)n-O2C-C6H4-CO2-)
*PE is Polyethylene thus an alkane (-CH2-CH2-)n
*PP is Polypropylene thus an alkane (-CH(CH3)-CH2)n

Alkanes are relatively inert towards hydrolysis reagents what is not the case of polyesters!