Dirty Plastic Can Be Turned Into Oil by Heating It Without Oxygen

When plastics can be sorted and reworked with reasonable effort, standard recycling is still the first choice. But a large share of waste cannot be handled economically that way.

That includes multilayer packaging, contaminated films, mixed polyolefins, the common plastics used in much packaging, and certain industrial residues. They are too mixed or dirty to sort and remelt at a reasonable cost.

Chemical recycling, particularly a process called pyrolysis, is attracting attention as a complement for those materials. It heats the waste in an oxygen-free chamber, so the plastic does not burn, and the heat splits the very long molecules that form plastic into much shorter pieces.

The main product is a liquid called pyrolysis oil, alongside gas and solid fractions. That oil can be used as feedstock for steam crackers, the large furnaces that normally turn petroleum into the building blocks for new polymers.

That offers a possible path for material that would otherwise go to landfills, incinerators, or unmanaged dumps. Making the oil, however, solves just one step, and the approach is still being developed.

Mixed waste carries dyes, stabilizers, flame retardants, fillers, and food residues into the oil. Compounds containing chlorine, nitrogen, oxygen, and silicon can corrode equipment and deactivate the catalysts used in chemical plants.

Steam crackers can now co-process only relatively small amounts of this oil, diluted with conventional fossil feedstocks. Using higher shares will require much cleaner oil, so the challenge has shifted from producing oil to purifying it.