Chemists Develop Process to Turn Previously Unrecyclable Plastics Into Propane

(Photo: Nick Fewings/Unsplash) Most of us have by now realized that conventional plastic recycling is more fantasy than reality. Despite our best attempts at separating out product packaging in the hope that some of it will be reused later, only 6 percent of the United States’ plastic waste is ever recycled. The rest of it ends up in landfills, in the ocean, or in other undesirable locations where it threatens local ecosystems and creates an unpleasant landscape.

Chemists are trying their hand at tackling that problem. A group of researchers at MIT have developed a process of turning previously unrecyclable plastics into propane, which can then be used as fuel or incorporated into a new product. Better yet, the process works for multiple types of plastic—a key element of any successful fight against plastic waste.

Disposable plastic goods don’t always share the same chemical makeup. Water bottles are made from a different type of plastic than milk containers, and your credit card is made up of a chemically different material than your red party cups. Sorting these materials not only takes time and money but also diverts some waste away from the recycling process entirely. But despite their differences, these plastics do have something in common: carbon and hydrogen, which make up a large portion of their chemical chains.

(Photo: Sigmund/Unsplash)

The chemists’ process, a type of hydrogenolysis, uses cobalt and zeolite (a grainy, porous substance) as a catalyst to break down polyethylene and polypropylene. In a reactor, the cobalt and zeolite work together to “edit” the plastics’ chemical makeup: The cobalt keeps the zeolite active as its pores limit the plastics’ molecular reactions. At the end of the process, a gas made primarily of propane emerges.

Propane has a number of uses, but its most recognizable is fuel, namely for household appliances, backyard grills, camping stoves, generators, and some farming equipment. It can also be used as a building block for new materials, like other plastics.

The process offers a way to recycle plastics that would otherwise be landfilled, but as with most things, it has its disadvantages. The reaction responsible for this chemical process is currently only done in small quantities, meaning it’ll need to be scaled up before it can be considered practical. Some plastics—like polyvinyl chloride, or PVC—would produce toxic gaseous byproducts if used alongside safer materials, so the process is far from perfect. Still, in a world with an increasingly problematic plastic waste problem, every bit helps.

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