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Polystyrene is relatively easy to depolymerize with enzymes, catalysts and moderate amounts of heat, see

https://pubs.acs.org/doi/10.1021/acssuschemeng.1c08400

The pyrolysis route they are using can be problematic because it produces carcinogenic aromatic compounds like

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

which has a metabolite which is almost a cancer-causing drug. In principle you could pyrolyze plastics all the way down to carbon monoxide + hydrogen syngas and then build that up to molecules you want with C1 chemistry

https://en.wikipedia.org/wiki/C1_chemistry

but most of the people who are trying chemical recycling by pyrolysis are trying to cook the molecules partially so the output fuel is a witches brew rich in hazardous aromatics. There is a lot of research into cleaner processes for chemical recycling such as

https://www.nature.com/articles/s41598-021-83659-2

and that one at the top but every large scale plant I've seen is a pyrolysis plant that's had to fight with environmentalists to start operations. From the viewpoint of a chemical engineer making fuel is for the birds because gasoline costs 50 cents a pound and (almost) any other chemical costs a lot more than that.



> Polystyrene is relatively easy to depolymerize with enzymes, catalysts and moderate amounts of heat

Wow. The paper from 2022 so surely noone is using this process yet, but are there any plans to? Any idea if it's practical? For expanded polystyrene?


That paper is not too remarkable, it's (1) the first one I found and (2) it uses extraordinarily mild conditions.

The gap between the bench and a commercial factory is immense and there are many areas where people write papers like this for decades but nothing really gets built. I think the usual excuse is that the factory is large enough that it needs to gather waste over a huge area and that transportation of EPS is prohibitively expensive. It doesn't help that styrene monomer is worth only 50 cents a pound, about the same as gasoline.




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