Pyrolysis is retrieving oil from plastic - generally, waste plastic and/or tires. Many types of plastic waste can be processed to yield back the petroleum it was originally made from.
Simply, this is a very clean process generating extremely low emissions of any type while waste plastics are 'distilled' or vaporized in a closed, air-tight vessel. The resulting vapor is then condensed, leaving oil in the process.
The only by-products are carbon black or black char and flammable gas. (Tires leave recyclable metal as well) The char is a non-toxic, marketable product for industry and the gas is a source of heat to continue the Pyrolysis process in the plant.
The resulting extracted oil is of higher quality than pump-grade diesel and burns with far less sulfur emission. This is a thoroughly tested industrial process with numerous plants operating 7 X 24 around the world.
Jobs are created while reprocessing vast quantities of generally free feed stock. Much of the floating, ocean-borne plastic waste can be relatively easily gathered. The plastic can even be handled when dirty. For example, waste mined from landfills. Separation of plastics in the home is best plus education about limiting the use of plastics/Styrofoam in the first place!