DFliyerz
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Polystyrene to Benzoic Acid
I'm away from home for a week and can't test this, but I wanted to run it by you guys before I attempted it. In my quest for benzene from household
chemicals, I came up with an idea to take polystyrene from say, plastic cutlery, crack it in a distillation apparatus (which should arrive by the time
I get home), and redistill the styrene. The next step would be to take potassium dichromate (which I got from a nearby pottery supplier), dissolve it
in water and oxidize the styrene monomer into benzoic acid, which could then be separated phasically with a separatory funnel as shown here. From there, it's an easy process to purify and convert the benzoic acid into benzene. So, what do you think?
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UC235
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A few points I could make here:
1) Dichromate isn't any less OTC than sodium benzoate, at least as far as I know. So, perhaps you are missing the point in your self-imposed exercise
and making way more work for yourself.
2) If dichromate even efficiently oxidizes alkenes to carboxylic acids, you will need a LOT of dichromate to do the job efficiently. Permanganate is
known to do this oxidation smoothly (though you'd be better off using toluene if available), is less toxic, and has fairly similar oxidizing capacity
per unit mass.
3) Redistillation of the styrene is probably wholly unnecessary and adds an extra yield reducing step. As long as it's liquid and can be efficiently
mixed with the oxidant solution, oligomeric material should be just as readily oxidized as monomer.
4) Have you considered hydrolysis of PETE plastic soda bottles with alkali hydroxide in a high-boiling polyol (there is a writeup in prepub). The
resulting terephthalic acid (or rather, disodium terephthalate made from it) should behave very similarly to benzoic in the standard dry distillation
as long as you use 2eq of NaOH and not 1 as is required for benzoic. Alternately, I remember seeing a paper where they simply mill the PETE finely,
mix with excess lime, and distill. The yield was not great, but it did produce benzene.
[Edited on 7-4-2015 by UC235]
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Zombie
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I'm not "tuned up" enough to comment on the process but it does seem an awful lot of work for a simple chemical, and very small yield.
I have a suggestion for a product I use daily that may simplify your process, and improve your yield.
Quote:
"This Styrene Wax is a 5% paraffin dissolved in styrene. When paraffin is added to resin, the wax will rise to the surface and protect the
curing resin from the inhibiting action of the air"
http://www.fibreglast.com/product/Styrene_Wax_71/Resin_Addit...
If Styrene is what you are after as a base for making Benzene... Make yourself an account with any supplier of fiberglass products. I pay 34.00 USD
per gallon for Styrene wax, and 15.00 USD per gallon of Benzene from the same supplier.
I do understand some chemicals are tougher to get in some areas but Fiberglass, and Polyester resins are universal. Most solvents are readily
available from these suppliers.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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DFliyerz
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For some reason, lots of chemicals are hard to get where I live. My local hardware stores don't sell toluene, sulfur, potassium permanganate, and a
lot of other things. Besides, I just want to be able to make chemicals from extremely common ones.
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Zombie
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I understand this.
That is why I suggested any fiberglass supplier. All the basics can be bought or converted for fun, and use.
They can all be bought at marine supply houses but for double the price or more. Stick with wholesale suppliers or create a wholesale account, and
order form the retailers.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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fusso
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Just ask: is it possible to oxidize PS directly to benzoic acid without pyrolysing to styrene?
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DraconicAcid
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Quote: Originally posted by UC235  |
4) Have you considered hydrolysis of PETE plastic soda bottles with alkali hydroxide in a high-boiling polyol (there is a writeup in prepub). The
resulting terephthalic acid (or rather, disodium terephthalate made from it) should behave very similarly to benzoic in the standard dry distillation
as long as you use 2eq of NaOH and not 1 as is required for benzoic. |
Apparently, this can also be done in water-ethanol
https://doors.doshisha.ac.jp/duar/repository/ir/15075/023052...
I might have to try this- I'm always on the lookout for new organic experiments for my students.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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JJay
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I am quite sure that potassium permanganate could oxidize styrene to benzoic acid.
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DraconicAcid
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Yes, but the question is about polystyrene.....
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Tdep
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Just thought I'd put forward my own efforts on this: https://www.youtube.com/playlist?list=PLnafk93vhO37mYIFCe8zQ...
You can make the terephthalic acid first, then do the decarboxylation, but the yields are quite low and the amount of benzene you get per amount of
time is very bad. So I shifted my focus to a 'one pot' reaction going from PET to benzene. I didn't have much success, but i'm sure there exists a set
of conditions that make this reaction worthwhile. Things to fix are:
- Getting fine PET. Grinding PET is impossible. If people could find some way of turning bottles into PET powder, it would improve this synthesis
dramtically
- Lower reaction temperature. It requires molten NaOH to proceed but at that temp the mix chars considerably, and sublimes off a yellow solid. If
somehow the reaction temp was brought down, say, with a eutectic mix maybe or some other catalyst, it would help yields a lot. No great sparks of
ideas for other options besides NaOH though.
- Keeping it one pot but somehow doing it in 2 steps. Maybe adding water, distilling off the water and then collecting the benzene? That extra time of
water + NaOH + PET would help to break up the PET a bit and start the hydrolysis, so the molten NaOH doesn't have quite as much 'heavy lifting' to do.
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Texium
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Thread Moved
9-5-2018 at 20:31 |
Rogueasset
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Has anyone tried putting the PET through a paper shredder repeatedly? How about a nutribullet? Coffee grinder? Freezing it with liquid nitrogen first
the one or all of the above?
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Rogueasset
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What about premelting it with a lot of nice clean sand. Enough so that you get a fine coating of melted PET on sand thus greatly increasing surface
area. Then cooling it and grinding it with one of the above methods.
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joseph6355
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Honestly, it would be much cheaper and easy to simply load a tin can with sodium benzoate and heat it in the stove until benzene vapors come out. Then
you just need to recondense it at the collecting flask.
Then I supposed you could use it as it or further purify it by redistilling it or washing it with water if you don't want to redistill it.
Oh, hello!  |
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Rogueasset
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| Quote: Originally posted by joseph6355 | Honestly, it would be much cheaper and easy to simply load a tin can with sodium benzoate and heat it in the stove until benzene vapors come out. Then
you just need to recondense it at the collecting flask.
Then I supposed you could use it as it or further purify it by redistilling it or washing it with water if you don't want to redistill it.
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What sort of yields are you getting with this process? Are you getting sodium benzoate cheap? I see all the free PET waste around and think that
bringing it back into service is better than it decomposing in landfill sites and clogging up the oceans and sealife.
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joseph6355
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| Quote: Originally posted by Rogueasset | | Quote: Originally posted by joseph6355 | Honestly, it would be much cheaper and easy to simply load a tin can with sodium benzoate and heat it in the stove until benzene vapors come out. Then
you just need to recondense it at the collecting flask.
Then I supposed you could use it as it or further purify it by redistilling it or washing it with water if you don't want to redistill it.
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What sort of yields are you getting with this process? Are you getting sodium benzoate cheap? I see all the free PET waste around and think that
bringing it back into service is better than it decomposing in landfill sites and clogging up the oceans and sealife. |
I can get Sodium Benzoate for 3.27 dollars a kilo.
NileRed reported a yield of 70%.
Actually, you will need sodium hydroxide too (I suppose other hydroxide salts will work too)
Honestly, what do you need benzene for? Maybe I need it too and just don't know what for yet.
Oh, hello! |
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