Less than a third of Europe's plastic waste is recycled, and most of that mechanically. The rest largely ends up in incinerators or landfill, even though it is a material made from crude oil. Chemical recycling offers a way to bring back into production the plastics that mechanical recycling cannot handle.
How mechanical recycling works
Mechanical recycling sorts, washes, shreds and melts plastic, then turns it back into pellets. The polymer molecules stay essentially the same; only the form of the material changes. It is a simple, energy-efficient route, and where the plastic is clean and of a single type, it should come first.
It does, however, have conditions. It needs clean, sorted streams of a single polymer, because a mix of different plastics will not melt into a good-quality material. And every time plastic is remelted, its properties deteriorate a little further.
Where mechanical recycling stops
A large share of plastic waste does not meet those conditions. It typically falls into four groups.
- Mixed plastics from separate collection that cannot be economically sorted by polymer.
- Contaminated plastics, such as packaging with food residue or used agricultural film.
- Multilayer packaging, where several different materials are bonded into a single film.
- Sorting residues left over once the valuable fractions have been picked out.
Today these materials mostly go to incineration or landfill. In the Czech Republic, Act No. 541/2020 Sb. bans the landfilling of recyclable and recoverable waste from 2030, so more and more companies and municipalities need another outlet. For anyone paying to dispose of such waste now, the obvious question is whether it could become a raw material instead.
How pyrolysis closes the loop
Chemical recycling, also called feedstock or tertiary recycling, works on the molecules of the plastic rather than its form. In pyrolysis, plastic is heated to 400–600 °C without oxygen and its long polymer chains crack into shorter hydrocarbons. The vapours condense into oil, the rest stays as gas, and a small amount of solid carbon remains in the reactor. Our article What pyrolysis is and how it differs from incineration covers the process in more detail.
The oil then goes to a petrochemical plant, where it is cracked into monomers such as ethylene and propylene. These are polymerised into new plastics that are chemically identical to plastics made from crude oil. The material returns to use without the loss of quality that repeated remelting brings.
According to the technology manufacturer, pyrolysis oil has up to 40% lower carbon footprint than the same feedstock from crude oil. For recycling statistics, though, the destination matters: only the route back into materials counts as recycling, while burning the oil in a boiler or CHP unit is energy recovery. We compare both routes in our article on what pyrolysis oil is used for.
Which plastics suit pyrolysis and which do not
Polyolefins and polystyrene work best, because they consist only of carbon and hydrogen. PET and PVC are a different matter: the oxygen in PET and the chlorine in PVC lower the quality of the oil, and chlorine also forms acid gases.
| Plastic | Typical sources | Suitability for pyrolysis |
|---|---|---|
| PE (polyethylene) | films, packaging | suitable |
| PP (polypropylene) | packaging, cups | suitable |
| PS (polystyrene) | cups, packaging | suitable |
| PET | bottles, trays | small shares only, otherwise separate beforehand |
| PVC | profiles, pipes | small shares only, otherwise separate beforehand |
Metals, glass and stone do not decompose in the reactor, and moisture lowers efficiency. That is why we analyse the waste composition before any feasibility study: it determines the yield and how much preparation the material needs before it goes in.
What plastics turn into
The mass balance of an industrial line running on plastics is 63% oil, 34% gas and 3% carbon. The oil has a lower heating value of around 39 MJ/kg, against roughly 43 MJ/kg for diesel, so even when it does not go to petrochemicals it has value as a fuel. Products registered under REACH can be sold as products rather than waste.
The gas fuels a CHP unit that covers the line's own demand of about 380 kW, so no permanent grid connection is needed. The carbon can be used as a filter sorbent, a concrete additive or an industrial raw material.
Mechanical and chemical recycling are therefore not competitors. Mechanical recycling handles clean, single-polymer plastics, and pyrolysis takes what would otherwise be burned or landfilled. Together they can return more plastic to use than either could on its own.
If you are looking for an outlet for plastics that mechanical recycling will not take, try a rough estimate in the calculator on our pyrolysis page.