A team of scientists from Tokyo Metropolitan University have devised a new chemical process that can upcycle polyesters, such as the polyethylene terephthalate (PET) in plastic water bottles, to morpholine amide. The reaction process is both high yield and waste-free, does not need chemicals, and is also easily scalable, helping to break the often expensive closed-loop recycling of plastic waste.

 

Recycling is key to fighting the mounting problem of plastic waste, but can be expensive since the recycling of polyesters tends to need power to make the required chemical reactions sufficiently hot, or strongly alkaline conditions that generate chemical waste. By the end of this process there are intermediate compounds that are used to make the same products they came from. This is often a wasteful process as well as not being very economically viable.

 

However, upcycling can break this closed loop and produce compounds from plastic waste that are more valuable and useful. Such an “open-loop” scheme is a crucial element of way to achieve the transition to a greener society. As detailed in the journal ACS Organic & Inorganic Au [Ogiwara, Y. and Nomura, K. ACS Org. Inorg. Au. (2023) DOI: 10.1021/acsorginorgau.3c00037], here a virtually waste-free approach to converting polyesters into morpholine amide, which is a useful building block that can then be converted into a variety of valuable chemical compounds, was developed.

 

Morpholine and a small amount of a titanium-based catalyst were used to turn polyesters into morpholine amides. In addition to being converted into intermediate compounds for making more polyester, they can also be easily reacted to produce ketones, aldehydes and amines, which are important families of chemicals for making many other compounds.

 

This new process does not need expensive reagents or harsh conditions, and is mostly free from chemical waste, offering an extremely high yield, with unreacted solvent being easily collected, and simple filtration working to separate the product. It is crucial that the main reaction is carried out at normal pressure, which means that no special reaction vessels or devices are used, making the reaction easily scalable.

 

The researchers, Yohei Ogiwara and Kotohiro Nomura, demonstrated the process by taking 50g of a PET material from a PET beverage bottle and reacting it with morpholine, getting more than 70 grams of morpholine amide, a yield of 90%. With global plastic waste being an increasing problem around the world, such innovative approaches will be needed to process and redeploy plastics.