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mowsala
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[*] posted on 21-10-2010 at 02:55
Benzene from PET


Like so many others, I want to make some benzene. I have read the benzene production pdf at http://www.sciencemadness.org/member_publications/benzene_pr... , and I have been thinking that maybe I could generate the benzoates in situ from bits of PET soda bottle.

Reading the article on PET pyrolysis at http://www.pm-kbase.com/articles/PETsdarticle(21).pdf, I see that pyrolysis of PET can yield nearly 50% benzoic acid, terephthalitic acid, and derivatives, with most of the rest going to worthless gases. So my idea is to heat hard a mixture of ground PET and sodium hydroxide, which might generate benzoic acid, which reacts with the NaOH to make sodium benzoate, approximating straight heating of sodium benzoate and sodium hydroxide, as discussed in the old pdf. Then I can just distill off the benzene.

I'm gussing that disodium terepthalate will act pretty similar to sodium benzoate when formed in terms of breakdown to benzene and sodium carbonate.

What do you reckon, will it work? I'm not expecting great yield, but since empty soda bottles are free and sodium benzoate is not, I think it could be quite worthwile.

[Edited on 21-10-2010 by mowsala]
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[*] posted on 21-10-2010 at 04:22


Ok, I think I missed this... http://www.sciencemadness.org/talk/viewthread.php?tid=14200#...
Should have read that first :P

Still, does anyone think this one-pot method could work?
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[*] posted on 21-10-2010 at 04:35


I doubt it will work.
Might be worth a try with a small amount.
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[*] posted on 21-10-2010 at 09:39


Quote: Originally posted by ScienceSquirrel  
I doubt it will work.
Might be worth a try with a small amount.


Are you saying the TPA + NaOH will not work at producing benzene?
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mowsala
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[*] posted on 21-10-2010 at 09:48


Ok, I've just tried it :)

20g of chopped PET bottle and 30g NaOH prills (way too much for a first try on hindsight) were put in a 100ml conical flask and a makeshift condenser attached. Heated strongly for 10-20 mins. The distillate was about 3ml of an orange, semi opaque liquid that floats on water with a strong and sickening smell which I suppose I would describe as alkene like (I don't know what pure benzene smells like). I've attatched a pic of the distillate on water in a little bottle.

I could have heated it for longer and got a bit more, but it was starting to get all blackened in the flask. The residue broke my flask on cooling, but I was half expecting that.

Well, this does sound fairly similar to the results of the well documented heating of sodium benzoate with NaOH in the old PDF: orange liquid distillate, etc. I know the yield was awful, but I think it could be well improved- lots of the PET had barely even melted in the flask.

So, what do you all reckon? Could my crude distillate be high in benzene? It sounds promising to me, but I haven't really got enough to distill or check boiling point, not with my equipment anyway.

distillate.jpg - 114kB
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Picric-A
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[*] posted on 21-10-2010 at 10:17


That looks very similar to the product i got form decarboxylation of TPA so yes that seems very promising! Yields are rather terrible though!
Dont forget that will be mixed with ethylene glycol, which is miscible with benzene, so you can at least half the amount of crude benzene you have for pure benzene. Separation is easy though.
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[*] posted on 21-10-2010 at 16:55


Benzene smells really good to me. Not like alkenes (or worse, 6 membered cycloalkenes). I'd say like toluene except ... sweeter and "heavier". Yeah, I know that sounds stupid but I couldn't think of anything else.



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[*] posted on 22-10-2010 at 00:54


That looks pretty good :) See if you can find a can to do it in next time, seeing as you're using copper tubing you could just have a fitting through a hole in the lid and clamp the lid of the can between the male and female threading on one of those things that makes a flange and seals off copper tube (don't know what they're called :P) I did the same to seal up the can for my benzene still except I wedged a 24/40 still head into the opening from the fitting instead.
Jeez benzene smelling sweet? To me it smells sharp and awful, quite different to toluene. Perhaps mine is still impure :/
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[*] posted on 22-10-2010 at 02:46


I agree with MagicJigPipe, I think benzene smells sweet and heavy. Toluene is different, I really like that odour. I don't like xylene's odour, unlike benzene and toluene.

Sometimes I can't resist smelling from a bottle of paint thinner occasionally (once every 3 weeks I think, contains toluene). I don't do this with benzene though.
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[*] posted on 22-10-2010 at 09:42


Thanks for the replies all! I will try it in a metal can with copper pipe next time, if I can construct such a thing, after a week in sunny Cornwall :cool:, then hopefully I will have enough to redistill, check boiling point, etc.

As for the smell of benzene, maybe it could be highly subjective? But I'm sure there's loads of crap in my crude orange oil.

And Picric-A, when you say about removing the ethylene glycol, you mean just wash it out by shaking with water, yes? Looking at that pdf on PET pyrolysis though, (which seems to have just dissapeared from the net, but you can still get on Google's HTML cache), it indicates that most of the ethylene glycol gets decomposed in the pyrolysis, but maybe the NaOH will change this.
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[*] posted on 5-1-2013 at 11:48


There is a thread on the German 'Versuchschemie' which set me off to try this.

Here a small scale test tube try from me and some impure benzene appeared....

<iframe sandbox width="640" height="360" src="http://www.youtube.com/embed/JhUxaNesnxs" frameborder="0" allowfullscreen></iframe>


[Edited on 2013-1-5 by metalresearcher]

[Edited on 2013-1-5 by metalresearcher]
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[*] posted on 5-1-2013 at 12:32


This seems like a more accessible route to small amounts of benzene for some of us, good work. I might try it soon if I have the time :P

Quote: Originally posted by MagicJigPipe  
Not like alkenes (or worse, 6 membered cycloalkenes). I'd say like toluene except ... sweeter and "heavier".


Tell me about it....I was using cyclohexene (from a 500ml bottle) in the school lab a few weeks ago, running numerous test-tube scale reactions. I was nearly sick.

I do like the smell of toluene, and ethyl acetate too for that matter:)




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[*] posted on 14-1-2013 at 17:52


Dear Sciencemadnessists,

Has anyone heard of the yield in weight in this pyrolysis? Like how many kg's PET it takes to yeild a kg of benzene? If this is worth the effort, I'm pretty jealous at those aware chemistry interested from Schweiz; this country has no deposit on PET, so you can just pickup full in one afternoon. PET-flasks are totally worthless in Schweiz, and they are left everywhere.

I'm very sceptic to gain any profit of producing benzene from PET where those are 30-50 US-cent worth in deposit. The weight of one kind of our 2L PET-flasks here in Europe is 40 grams, and 1 kg of those flaskes are 25 pieces, which is 8,60 USD. I can imagine that for produce 1 kg benzene, it takes at least 10 times the weight of PET - which is very roughly at least 86 USD. This is expensive benzene.
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[*] posted on 15-1-2013 at 06:52
Benzene


Sodium Benzoate is a food additive readily available and cheap, so why waste time making it. You can get three pounds for around $20.00 on eBay.


Quote: Originally posted by mowsala  
Like so many others, I want to make some benzene. I have read the benzene production pdf at http://www.sciencemadness.org/member_publications/benzene_pr... , and I have been thinking that maybe I could generate the benzoates in situ from bits of PET soda bottle.

Reading the article on PET pyrolysis at http://www.pm-kbase.com/articles/PETsdarticle(21).pdf, I see that pyrolysis of PET can yield nearly 50% benzoic acid, terephthalitic acid, and derivatives, with most of the rest going to worthless gases. So my idea is to heat hard a mixture of ground PET and sodium hydroxide, which might generate benzoic acid, which reacts with the NaOH to make sodium benzoate, approximating straight heating of sodium benzoate and sodium hydroxide, as discussed in the old pdf. Then I can just distill off the benzene.

I'm gussing that disodium terepthalate will act pretty similar to sodium benzoate when formed in terms of breakdown to benzene and sodium carbonate.

What do you reckon, will it work? I'm not expecting great yield, but since empty soda bottles are free and sodium benzoate is not, I think it could be quite worthwile.

[Edited on 21-10-2010 by mowsala]




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[*] posted on 15-1-2013 at 07:43


if you have to, just oxidize toluene to it's terminal state, and proceed as above. if you can't find sodium benzoate on e-bay, it is sold by apple growers professional supply companies.
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[*] posted on 15-1-2013 at 18:00


Quote: Originally posted by mowsala  
Thanks for the replies all! I will try it in a metal can with copper pipe next time, if I can construct such a thing, after a week in sunny Cornwall :cool:, then hopefully I will have enough to redistill, check boiling point, etc.

As for the smell of benzene, maybe it could be highly subjective? But I'm sure there's loads of crap in my crude orange oil.

And Picric-A, when you say about removing the ethylene glycol, you mean just wash it out by shaking with water, yes? Looking at that pdf on PET pyrolysis though, (which seems to have just dissapeared from the net, but you can still get on Google's HTML cache), it indicates that most of the ethylene glycol gets decomposed in the pyrolysis, but maybe the NaOH will change this.


Did you distill into water, say was there water in the receiving flask from beginning?

For your picture and description of smell are almost exactly what I got when doing the benzoate/NaOH without water in the receiver. And for what reason I dunno, adding water later did not help so much, results with water from start were far better. I was not not the only one making this experience, but it is everything in the Benzene thread, somewhere, its a long one....
Redistillation of water/destillate gave perfect great smell benzene of high purity leaving a small residue of sharp smelling morning piss like colored gunk behind.

/ORG
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[*] posted on 20-1-2013 at 15:14


Quote: Originally posted by Palladium  
I'm very sceptic to gain any profit of producing benzene from PET where those are 30-50 US-cent worth in deposit. The weight of one kind of our 2L PET-flasks here in Europe is 40 grams, and 1 kg of those flaskes are 25 pieces, which is 8,60 USD. I can imagine that for produce 1 kg benzene, it takes at least 10 times the weight of PET - which is very roughly at least 86 USD. This is expensive benzene.


Here, we find PET bottles in the streets all the time. They are often crushed so the recycling machine would not accept it anyway.
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