From time to time, people here talk about the potential for burning plastic waste in a rocket mass heater or other stove that reaches high temperatures. And almost always, the conventional response is that one should not do this because one risks forming dioxins by doing so.
I certainly do not wish to take the problem of dioxins lightly, and I understand that "backyard barrel" burning of plastic trash leads to a significant portion of all the dioxin pollution produced worldwide. However, I think that this question calls for serious analysis by an expert in chemistry and/or chemical engineering, and that it likely is safe to burn some types of plastic if the proper precautions are taken. Often the concern about dioxin ignores that different plastics are wildly different in chemistry.
Unfortunately, I am not an expert in chemistry, so I would be very interested if one can critique the following argument:
- Toxic dioxins all contain chlorine, fluorine, or bromine atoms. If there is no source of one of these halogens, no dioxins can be formed.
- Clean polyethylene and polypropylene are some of the most common waste / single use plastics, and have a very simple molecular structure, essentially the same as paraffin wax (or, for that matter, diesel fuel) only much longer and larger. They should burn cleanly if heated hot enough.
- There should not be any source of halogens in these fuels, so no dioxins should be able to be formed.
- Dioxins are mostly a concern when PVC or other plastics that contain halogens or halogen-containing additives are burned.
I can see the following potential issues:
- Do "clean" polyethylene and polypropylene actually contain significant quantities of additives or contaminants that do provide enough halogens to form dioxins?
- Or will the wood or other surface or atmospheric contaminants provide enough halogens? Does the plastic have to be immaculately free of salt for this to work?
- Are there non-halogen-requiring toxins of sufficient potency that the whole project should be dropped (and burning kerosene or wood shouldn't be)?
- Is identifying safe plastic waste to burn a futile task?
I DON'T KNOW the answer to any of these questions, and I think the topic deserves a serious, critical investigation as opposed to the cautionary approach that's been taken so far.
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