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aga
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On taking the rig to bits, a large volume of HCl escaped.
Clouds of it everywhere.
0.08[M] HCl collected roughly equals 13% of the available Cl extracted (2.84g / 21.44g).
Some of the PVC has disintegrated into fine black dust/grains.
A lot of it is still in a solid, porous, pliable mass, and looks black and shiny.
Definitely not PVC as we know it anymore.
Reminds me a lot of the shiny rock stuff in steel slag.
That lump wouldn't come out or break up, so i stuffed handfuls of dry weeds in with it to let it have another go.
I'd expect the temperature to about 300C ish in the pot.
Definitely need some bigger square steel section 
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blogfast25
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Quote: Originally posted by aga  | 0.08[M] HCl collected roughly equals 13% of the available Cl extracted (2.84g / 21.44g).
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Correct. And going by the escaped gas, considerably more.
Going by the rest, it looks like significant decomposition was achieved, but I'm surprised there didn't seem to be much condensable organic matter.
Perhaps more time would achieve that.
Perhaps a cold trap after the HCl trap might also reveal more low boiling organics?
[Edited on 29-9-2014 by blogfast25]
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aga
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The idea was to use a 10 gallon steel tank and multiple burners, at least 2 condensers and some other stuff.
Oxirane beat me to it with his steel pot, so i *had*to rig this up and try it.
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blogfast25
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Palavering a bit more, since as we're reasonably sure HCl comes off, the following structural rearrangement (HCl elimination reaction) must at least
in part take place:
[-CHCl-CH2-]<sub>n</sub> --- > [-CH=CH-]<sub>n</sub> + n HCl
... giving rise to oligomeric structures like -CH=CH-CH=CH-CH=CH-CH=CH- etc.
Cyclisation of this conjugated structure could give rise to benzene and a plethora of other stuff, as suggested in the paper Oxirane linked to on the
previous page.
[Edited on 29-9-2014 by blogfast25]
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Oxirane
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Gotta get you guys some pics on my setup next time I go to my workshop.
But my outcome was somewhat similar to aga's. The PVC was not much disintegrated and actually most part of it was quite intact. This is because I did
not bring the process to an end but stopped it when there became those minor issues I mentioned. The vapor tube from the receiver which was PVC tubing
got full of black tar and I was afraid of it blocking and causing burst from the receiver connector, and major amounts of HCl gas was released to
atmosphere from the HCl water flask because of temp increase. This was quite un-scientific proof-of-concept-work in which I just dumped some PVC in
and heated it up, but it gave the most important result: it does generate HCl and it does it in very good yield.
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aga
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That it does !
Question is, What to chuck in there with the PVC to push the reaction(s) towards Benzene (or whatever) as well ?
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blogfast25
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This could also be the object of a smaller, more quantitative lab test: boiling tube with PVC (heated by furnace of Bunsen), leading to small Liebig
condenser, leading into anti-suck back trap (trapping also stuff like benzene), leading to HCl water trap, leading to cold trap.
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blogfast25
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| Quote: Originally posted by aga | | Question is, What to chuck in there with the PVC to push the reaction(s) towards Benzene (or whatever) as well ? |
Something that favours cyclisation. Need to look at some catalysts for that...
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aga
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Iron wool, bits of verdigris-covered copper tube then !
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blogfast25
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Huh?
A starting point for choice of catalyst is to understand the cyclisation reaction itself better, of course.
[Edited on 29-9-2014 by blogfast25]
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blogfast25
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One can try to imagine a possible cyclisation reaction as the bridging between carbon atoms 1 and 6, in 'badly drawn boy', here:
Can't be that hard, now cannit? 
[Edited on 29-9-2014 by blogfast25]
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aga
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Nah. Lose some H and it's given.
What likes H more than C does, but isn't O or Cl ?
Oh yeah. OH.
So lob some NaOH in with the PVC ?
OH attack on pos 1 pushes electron density into the (left) CH, ejecting it, straining the ring, consequently rippling back and ejecting the CH on pos
6, leaving 1 and 6 nowhere to go but each other's open arms.
(I just made that up. It's unlikely to be reasonable, let alone true.)
Edit:
Forgot it's OC for second. All above fantasy via 10 intermediates.
[Edited on 29-9-2014 by aga]
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blogfast25
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An unusual way to prepare NaCl?
Last night I was doodling some more possible conformations of highly unsaturated, conjugated oligomers (residue from HCl elimination reactions) and
came up with one that could be the most promising for cyclisation. Will upload tonight.
Any catalyst we throw in there had better be cheap because catalyst recovery from the gunk will be near impossible.
[Edited on 30-9-2014 by blogfast25]
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aga
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Doh !
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blogfast25
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Latest doodlings.
Imagine a longish stretch (at least 8 C atoms long) of PVC that has been subjected to HCl elimination reactions.
Imagine this now in the top conformation. By, erm, thermal rearrangement [cough!] atoms 1 and 6 could then link up to form benzene and more conjugated
bonds are left in the part that was split off.
The dotted line between 2 and 5 represents the conjugated double bonds between 2 and 3 and between 4 and 5.
1 tentative mechanism for 1 compound, 49 or so to go!
[Edited on 30-9-2014 by blogfast25]
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aga
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Seems that in this polymer, the Position of the Cl is random, so randomly twisted chains would randomly allow two Cl to meet, possibly causing them to
eject as Cl2 , leaving the remaining C-H to latch on to other local C-H, occasionally forming Benzene, most times forming other stuff.
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blogfast25
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| Quote: Originally posted by aga | | Seems that in this polymer, the Position of the Cl is random, so randomly twisted chains would randomly allow two Cl to meet, possibly causing them to
eject as Cl2 , leaving the remaining C-H to latch on to other local C-H, occasionally forming Benzene, most times forming other stuff.
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Possibly but it seems most chlorine leaves as HCl, not Cl<sub>2</sub>.
Also, you'd still have to break two strong C-Cl bonds, for instance:
-CH<sub>2</sub>-CHCl-CH<sub>2</sub>-(add some units)-CH<sub>2</sub>-CHCl- [twisted conformation] ===>
Cl<sub>2</sub> + cyclic compound
would have a positive ΔH, according to the bond enthalpies. The entropic term - TΔS would then have to save the day. It's not impossible, it just
doesn't seem to happen much in reality.
[Edited on 30-9-2014 by blogfast25]
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aga
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| Quote: Originally posted by blogfast25 |
Possibly but it seems most chlorine leaves as HCl, not Cl<sub>2</sub>.
.. you'd still have to break two strong C-Cl bonds ...
... would have a positive ΔH, according to the bond enthalpies.
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[CH3Cl]n -> Sos + HCl
Perhaps the HCl is the most stable product that can be detected easily, and forms as a result of various intermediate reactions, of which there will
probably be a great many.
The +ΔH is fine : we're pouring energy into this thing.
OC must be at least Partly guesswork to have gotten anywhere.
It's simply far too complex to be totally certain.
The PVC chain is 100s of 1000s of vinyl groups long.
How do OC chemists cope with thinking about the multitude of possible side reactions ?
Is this where NMR, GC etc became Required just to get a clue ?
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blogfast25
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Another strong argument against Cl<sub>2</sub> is the following. Take 1,6 dichlorohexane: Cl-(CH<sub>2</sub><sub>6</sub>-Cl. On heating it does not split off chlorine.
But use a Cl scavenger like an alkali metal and then:
2 K + Cl-(CH<sub>2</sub><sub>6</sub>-Cl === >
(CH<sub>2</sub><sub>6</sub> [cyclohexane] + 2 KCl becomes
highly thermodynamically favourable (I'm not claiming this is a practical method to prepare cyclohexane, I don't know that).
(Don't try this at home: mixtures of haloalkanes and alkali metals are known to be explosively unstable!!)
Good point about the +ΔH!
Unravelling OC reaction mechanisms require some guess work, yes. More so here with this myriad of possibilities (see the paper Oxirane linked to for
pyrolysis products of PVC).
All kind of analytical techniques can assist in solving the puzzle, including IR, GC, NMR and mass spectrometry (among others).
| Quote: Originally posted by aga | Perhaps the HCl is the most stable product that can be detected easily, and forms as a result of various intermediate reactions, of which there will
probably be a great many.
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We know from literature that the Cl is almost quantitatively recoverable but as HCl. Chlorine is also easy to detect (use nose but sparingly!)
[Edited on 1-10-2014 by blogfast25]
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Little_Ghost_again
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Really interesting way to get Hydrochloric acid! Great thread
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aga
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I must have been designed for OC as i have a Big nose (plenty of tests before dissolution)
Got a bloke making me 6 bigger burners for the 10 gallon tank.
Ready by Friday evening he says ...
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blogfast25
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| Quote: Originally posted by aga | [Got a bloke making me 6 bigger burners for the 10 gallon tank.
Ready by Friday evening he says ... |
Natural Gas? (I'm thinking of your BB...)
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Oxirane
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You might wanna go look for BBQ burners. Those bitches breath up to 6000 watts of heat. Remember also that insulating the reactor will significantly
ease the heating. I use normal rockwool. Didnt remember to take pics. 
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Little_Ghost_again
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Ok I am going to stop reading this thread now, I found some PVC pipe off cuts in a shed . The temptation to have a go is increasing, so for the sake of safety I will follow no more . good luck though, its a really neat way to do something with a waste product
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aga
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Insulation yes. Not Rockwool, but a star-wars-ti-fighter arrangement to duct the hot air.
It will certainly raise the 'reactor' temperature a bit.
I drilled a hole and welded a sealed stainless steel pipe into the 'reactor' so a thermometer can get in there - isn't Science with no measurements.
Least Fuel possible, hence the rocket stoves.
The Fuel can be the Reactant as well.
Collect some twigs, burn some, pyrolyse the rest.
Temptation is to pyrolise a few kg PVC, but wood seems more interesting (got enough HCl at the mo).
Weight the Total mass, split it into Reactants and Fuel, all weighed, then see what the results are.
All Good. Roll on Saturday.
Quick Vote : pyrolise Wood or PVC first ?
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