swan
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Rubber decomposition in molten zinc
A method for recycling car tyres is being developed that immerses tyres in molten zinc at around 430 C.
Can anyone speculate possible reactions with molten zinc and polymers of styrene-butadiene, polyisoprene and polybutadiene? Are any organozinc
compounds likely to form? Will the molten zinc have any catalytic cracking characteristics?
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unionised
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I think they are using zinc to transfer heat rapidly to the tyres.
Molten metals are good conductors of heat and reasonably stable. I guess they chose zinc because it's fairly cheap, melts easily and its compounds are
not very toxic.
I doubt there are any chemical reactions involving the zinc.
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bbartlog
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If the rubbers contain any sulfur or chlorine, I'd expect it to end up as ZnS or ZnCl2.
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ScienceSquirrel
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I suspect the original poster is referring to this process that uses a bath of molten zinc chloride, not molten zinc;
http://nepis.epa.gov/Exe/ZyNET.exe/2000THMJ.txt?ZyActionD=Zy...
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swan
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A liquid heat transfer medium whether it be molten zinc metal or zinc chloride is not in contact with the decomposing polymer because it is shielded
by the matrix of carbon black (around 40%) mixed with the rubber.
Vapourisation of smaller species and detachment of oligomers is occuring in the polymer melt zone and these vapours are diffusing thru the surrounding
carbon layer to form bubbles at the interface with the molten zinc.
We assume the polysulphide vulcanising crosslinks will break early in the process. The bulk of the vapour seems to consist of isoprene, styrene,
dipentene, butadiene etc. It’s the likely reactions when the vapour is moving up thru the molten zinc metal as a bubble that are of interest.
As the bubbles break the surface, a spongy floatation layer forms indicating possibly sulphides and organozinc compounds.
The differences between using molten zinc chloride as with the 1984 project and molten zinc metal are still to be determined.
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