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Plastic waste is one of the most pressing environmental problems in our time. Classifying different types of plastic waste makes recycling difficult.
Now, engineers at the Massachusetts Institute of Technology (MIT) have developed an effective new catalyst that can decompose mixed plastics into propane, which can then be burned as fuel or used to make new plastics.
Plastics are ubiquitous in our modern world, which means that a large number of plastics will eventually enter the environment, and it is worrying that few places are not affected. Now, plastic can be found from the South Pole to the North Pole, from the sea bottom to the top of Mount Everest, and it is moving up the food chain, so that now we can also find plastic in our bodies.
Plastics have very strong carbon bonds, which make them elastic and reliable in use, but it is very troublesome to recycle them. Even worse, different types of plastics require different recycling methods, making it difficult to classify and recycle them on a large scale. But MIT's research team has now proposed a new technology that can handle a variety of plastics mixed together and convert them into propane, which has many uses.
The key to solving the problem is a catalyst, which consists of a porous crystal called zeolite, filled with cobalt nanoparticles. The researchers pointed out that other catalysts will break the carbon bond in unpredictable places to produce different final products, while new catalysts will only break the carbon bond in a specific, repeatable location
This position means that it basically cuts off the propane molecule, leaving the remaining hydrocarbon chain, ready to repeat the process. This applies to many types of plastics, including the most commonly used plastics, such as polyethylene (PET) and polypropylene (PP).
In the test of mixed plastic samples in the real world, the research team found that this process can convert about 80% of plastic into propane, without producing methane as a by-product. Methane is the second largest greenhouse gas producer after carbon dioxide (CO2).
The resulting propane can be directly used as a relatively low impact fuel, or as a raw material to manufacture new plastics in a partially closed cycle system.
Most importantly, the catalyst components (zeolite, cobalt and hydrogen) are relatively cheap and readily available. This research result has been published in the journal JACS Au recently.
Although this research is very attractive, the researchers said that future work will need to focus on how this technology is applied in the real world plastic recycling stream, and how pollutants such as glue and labels affect this technology.