The global accumulation of plastic waste is an ever-growing problem. At least five billion tons of the stuff has accumulated on land and sea and is even showing up in the bodies of animals and humans. Recycling plastic instead of making even more of it seems like an essential thing to do but it has proven to be extremely challenging.
The main problem is that plastics come in many different varieties and the ways of breaking them down into a form that can be reused are very specific to each type of plastic. Sorting plastic waste by plastic type is extremely impractical at large scale. Certainly, most consumers can’t do it themselves. As a result, most plastic gathered in recycling programs ends up in landfills.
New research at MIT has developed a chemical process using a catalyst based on cobalt that is very effective at breaking down a variety of plastics, including polyethylene and polypropylene, which are the two most widely produced plastics. The MIT process breaks plastics down into propane. Propane can be used as a fuel or as a feedstock for making many different products, including new plastics.
Plastics are hard to recycle because their long-chain molecules are very stable and difficult to break apart. Most chemical methods for breaking their chemical bonds produce a random mix of different molecules which would somehow have to be sorted out in order to be useful for anything.
The new process uses a catalyst called a zeolite that contains cobalt nanoparticles. The catalyst selectively breaks down various plastic polymer molecules and turns more than 80% of them into propane.
The researchers are still studying the economics and logistics of the method, but it looks quite promising.
Photo, posted April 25, 2016, courtesy of NOAA Coral Reef Ecosystem Program via Flickr.