Polyolefin plastics like

https://en.wikipedia.org/wiki/Polyethylene

and

https://en.wikipedia.org/wiki/Polypropylene

and even

https://en.wikipedia.org/wiki/Polystyrene

are "solid hydrocarbons" but most plastics are more complex than that. One reason we quit burning trash in many places is the presence of

https://en.wikipedia.org/wiki/Polyvinyl_chloride

which produces HCl which eats the incinerator. [1] Sure you can build a chemically tougher incinerator and add lime but practically stripping toxins from incinerators is a function of building a stripper tuned to whatever toxins are expected to be in the particular waste and frequently adding something that reacts with them. You can't really "burn up" heavy metals and certain other poisons and those either go up the stack or are part of the ash that has to be disposed of.

A technology you hear about more than you hear about real implementations is "chemical recycling of plastics" through pyrolysis which implement more or less controlled combustion and captures petrochemical molecules that can be used either for fuel or to make plastics and other chemicals: these manage to capture or consume most of the products but some of the polycyclic aromatic hydrocarbons that are produced when you burn plastic are practically drugs that cause cancer

https://en.wikipedia.org/wiki/Benzo(a)pyrene

[1] Plenty of others contain oxygen: https://en.wikipedia.org/wiki/Polyethylene_terephthalate or nitrogen such: https://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styren... and https://en.wikipedia.org/wiki/Nylon

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ars 2 days ago | parent [-]

Most disposable plastic is not PVC. Because Chlorine prolongs the life of the plastic, it's specifically used on things that you don't throw out.

In any case incinerators can handle the chlorine - it's so reactive that it's actually very easy to filter.

> You can't really "burn up" heavy metals

There are no heavy metals in plastic, and very little in consumer waste as a whole.

> are "solid hydrocarbons" but most plastics are more complex than that

But those 3 you listed are the vast majority of the thrown out plastics.

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PaulHoule 2 days ago | parent [-]

Municipal waste has a large fraction of waste from demolished buildings which includes wood, concrete, bricks, all sorts of stuff. PVC is a significant part of that waste because it is used for siding, floors, etc.

In a consolidated municipal waste stream heavy metals are a concern because they concentrate in the ash which has to be carefully stored. This kind of system

https://en.wikipedia.org/wiki/Plasma_gasification

is supposed to encapsulate heavy metals into slag particles that aren't very mobile and can be incorporated into roads, building aggregates and such but people have struggled to make them work, part of it is that the syngas plant and whatever uses the syngas and cleans up the syngas and/or the products of using the syngas is a chemical factory that depends on the inputs having a certain composition and the composition of a municipal waste stream is not at all constant.

PET is a major thrown-out plastic that's not a hydrocarbon, it's also the most recycled. Polystyrene, funny enough, is easy to chemically recycle but not through pyrolysis, it's the sort of thing you might even demo in a high school chemistry class if styrene wasn't so carcinogenic. It's never caught on because expanded polystyrene is hard to handle, transport and bring back to a chemical factory large enough to efficiently consume.

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ars 2 days ago | parent [-]

How is PET not a hydrocarbon (for the purposes of burning it)? It's (C10 H8 O4)n the oxygen makes it not technically a hydrocarbon, but it will burn just fine and cleanly.

Your point about building waste is valid, but I think most of that stuff goes in dumpsters and can be directed to a different wasting handling.

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lstodd 2 days ago | parent [-]

Hah.

We burned shavings/rejects from a polyester-resin+glass boat building.. in a 200L drum.

That was quite smoky and smelly, but still I think better than just shipping it all off for burying in a landfill. And fiberglass decomposed basically into fine sand too.

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kragen 2 days ago | parent [-]

Environmentally speaking, shipping it off to a landfill would have been orders of magnitude better; burning it released thousands or millions of times more pollution. Most polyester resins are aromatic, so incomplete combustion can produce a wide variety of quite toxic substances.

	▲	lstodd 2 days ago \| parent [-]
		I guess we did release some. Mostly soot and half-burned hydrocarbons to be decomposed by solar UV. Still, thinking of all this just being buried for like 2e6 years ... that seems even more wrong.