The widespread use of large volumes of plastics has created serious environmental issues. Polyethylene and polypropylene make up more than 60% of the total plastic content of municipal solid waste. These plastics originate primarily from fossil fuels.
Scientists in the United States and China have now developed a method of efficiently turning these plastics back into useful fuels and chemical feedstocks.
Polyethylene is the largest-volume plastic in the world, with annual production exceeding 100 million tonnes. It is remarkably inert and difficult to degrade without special treatment. Currently, thermal and catalytic pyrolysis at high temperatures (typically above 400°C) is required. These processes suffer from low energy efficiency and lack of product control, often resulting in the formation of complex product compositions, including hydrocarbon gas, oil, wax, and char.
Now scientists from the University of California Irvine and the Shanghai Institute of Organic Chemistry have developed a method for the highly efficient degradation of polyethylenes under mild conditions (at 175°C). In a two-stage process, using widely available, low-value, short alkanes, such as petroleum ethers, as catalysts, different types of polyethylenes with various molecular weights can be completely converted into useful liquid fuels and waxes.
The method allows common plastic wastes, such as polyethylene bottles, bags and films to be converted into valuable chemical feedstocks without any pretreatment.
The researchers are now aiming to improve the efficiency of the process, including increasing catalyst activity and lifetime, reducing running costs, and developing the processes to turn other types of plastic waste into usable products.