Researchers at Tokyo Metropolitan University have developed a new chemical process that recycles polyesters, including PET from plastic bottles, into morpholinamide, a valuable and versatile building block that can be used to synthesize a wide range of compounds. The reaction is high-yield, waste-free, requires no harmful chemicals, and is easily scalable. The team successfully broke out of the often costly closed-loop recycling cycle of plastic waste and cycled upwards, producing more valuable products.
Traditional recycling and upcycling
In the fight against plastic waste, recycling plays an integral role. But at what cost? In the case of polyester recycling, which includes polyethylene terephthalate (PET) in plastic bottles, electricity is often required to bring the required chemical reactions to high enough temperatures, or strongly alkaline conditions are required to create chemical waste. Finally, the intermediate compound we get is used to make the same product. Not only would this be wasteful, it would also be economically unfeasible.
This is where the "upward" cycle comes from. Scientists have been working to break this closed cycle and create compounds from plastic waste that are more valuable and useful to society. "Open-loop" programs like this are an important part of a practical strategy to help us transition to a green society.
Breakthroughs in Chemical Transformations
Now, a research team led by Associate Professor Yohei Ogiwara and Professor Mitsuhiro Nomura of Tokyo Metropolitan University has proposed a method that generates almost no waste to convert polyester into a multifunctional building block that can be converted into a variety of valuable compounds. They used an inexpensive solvent called morpholine and a small amount of a titanium-based catalyst to convert the polyester into morpholinoamide. Not only can they be converted into intermediate compounds that make more polyester (recycling), they can also easily react to produce ketones, aldehydes, and amines, all important families of chemicals that can be used to make a host of other more valuable compounds (upcycling).
The new process requires no expensive reagents or harsh conditions and produces almost no chemical waste. Yields are very high and any unreacted solvent can be easily collected. They also found that only a small amount of catalyst was needed to drive the reaction at a reasonable rate, and all that was needed to isolate the product was simple filtration. A key point emphasized by the research team is that the main reaction occurs at normal pressure, which means no special reaction vessels or equipment are required. This makes the reaction easily scalable even in the laboratory. The research team proved this by extracting 50 grams of PET material from an actual PET beverage bottle, reacting it with morpholine, and obtaining more than 70 grams of morpholinamide, with a yield of 90%.
Impact and future potential
As the global plastic waste problem grows, bold new strategies are needed to deal with plastic and reintegrate it into society. As a low-cost, waste-free upcycling option, the team's findings may soon be applied to convert polyester waste into specialty chemicals.