Scientists Figured Out How to Recycle Plastic by Vaporizing It

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A new technique could prevent tons of waste in the future—if it can scale.

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 UC 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 gases at room temperature. Those gases 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.

Breaking It Down

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.

While isomerizing ethenolysis had been tried by the same researchers before, the previous catalysts were expensive metals that did not remain pure long enough to convert all of the plastic into gas. Using sodium on alumina followed by tungsten oxide on silica proved much more economical and effective, even though the high temperatures required for the reaction added a bit to the cost.