Vaporizing Plastics Recycles Them Into Nothing but Gas

Arthur T Knackerbracket has processed the following story:

Our planet is choking on plastics. Some of the worst offenders, which can take decades to degrade in landfills, are polypropylene-which is used for things such as food packaging and bumpers-and polyethylene, found in plastic bags, bottles, toys, and even mulch.

Polypropylene and polyethylene can be recycled, but the process can be difficult and often produces large quantities of the greenhouse gas methane. They are both polyolefins, which are the products of polymerizing ethylene and propylene, raw materials that are mainly derived from fossil fuels. The bonds of polyolefins are also notoriously hard to break.

Now, researchers at the University of California, Berkeley have come up with a method of recycling these polymers that uses catalysts that easily break their bonds, converting them into propylene and isobutylene, which are gasses at room temperature. Those gasses can then be recycled into new plastics.

Because polypropylene and polyethylene are among the most difficult and expensive plastics to separate from each other in a mixed waste stream, it is crucial that [a recycling] process apply to both polyolefins," the research team said in a study recently published in Science.

The recycling process the team used is known as isomerizing ethenolysis, which relies on a catalyst to break down olefin polymer chains into their small molecules. Polyethylene and polypropylene bonds are highly resistant to chemical reactions because both of these polyolefins have long chains of single carbon-carbon bonds. Most polymers have at least one carbon-carbon double bond, which is much easier to break.

[...] The reaction breaks all the carbon-carbon bonds in polyethylene and polypropylene, with the carbon atoms released during the breaking of these bonds ending up attached to molecules of ethylene.The ethylene is critical to this reaction, as it is a co-reactant," researcher R.J. Conk, one of the authors of the study, told Ars Technica. The broken links then react with ethylene, which removes the links from the chain. Without ethylene, the reaction cannot occur."

The entire chain is catalyzed until polyethylene is fully converted to propylene, and polypropylene is converted to a mixture of propylene and isobutylene.

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