Professor Kotohiro Nomura’s research group at Tokyo Metropolitan University has developed an efficient method for the exclusive depolymerization of PET (polyethylene terephthalate)*1, PET bottles and textile wastes, using alcohols and an inexpensive, readily available and earth-abundant iron catalyst. This method can provide a new possibility for the selective chemical conversion of polyesters, an important key technology for circular economy.
Plastic waste has been a serious environmental problem that needs to be resolved urgently. However, the current situation is that most of it is reused as fuel and the percentage of material reused is still low. Polyester*2, which is formed by repeated “ester bonds” created by the reaction of a carboxylic acid and an alcohol—particularly PET—has been a commodity plastic widely used for bottles, textiles, carpets, curtains, etc. PET bottles have been recycled mostly by material recycling (collection, sorting, reuse), but the quality of the recycle resin is generally inferior to the virgin resin. Therefore, the importance of developing a "chemical recycling*3" method that cuts the ester bonds and efficiently returns them to chemical raw materials has been recognized recently. However, the conventional methods require high temperatures and large amounts of acid and/or inorganic/organic base. Therefore, a simple, inexpensive, and environmentally friendly method has been desired.
The research team has now developed a simple acid- and base-free method for quantitative chemical recycling of PET waste bottles, textile waste by depolymerization with alcohol, using iron catalyst system producing the corresponding terephthalic acid diesters [dimethyl terephthalate (DMT), diethyl terephthalate (DET), bis(hydroxyethyl) terephthalate (BHET) etc.] exclusively (99.7 to 99.9 % yield) even under scale-up conditions. Addition of a minuscule amount of amine enhanced the catalytic activity without compromising selectivity. The catalyst system consisting of iron(III) chloride (FeCl3), which is inexpensive and widely available, and a certain amine demonstrated superior catalyst performance at 120-180 ºC. The method also enables the selective depolymerization of PET from a mixture of cotton and other plastics. This method of exclusive chemical recycling of PET from plastic wastes offers a promising solution for achieving a circular economy.
The research was conducted under the Japan Science and Technology Agency (JST) CREST program, Research Area “Precise Material Science for Degradation and Stability,” Research Theme “Development of Bio-Based Advanced Polymers and their Depolymerization, Chemical Recycle.”
The research paper is as follows. “Quantitative Chemical Conversion of PET Waste Bottles, Textile Wastes by Exclusive Transesterification with Alcohols by FeCl3–Amine Catalyst Systems,” ACS Sustainable Resource Management, November 12, 2025,
doi: 10.1021/acssusresmgt.5c00447
＜Notes＞
(*1) PET (polyethylene terephthalate)
Commodity plastic widely used as bottles, textiles, carpets, curtains, etc. PET, poly(ethylene terephthalate), consists of the ester bond (described below) between terephthalic acid and ethylene glycol.
(*2) polyester
The chemical bond (R'COOR) formed by dehydration of the hydroxyl group (ROH) of an alcohol and the carboxy group (R'COOH) of a carboxylic acid is called an ester bond, and a polymer formed of repeating units of ester bonds is called a polyester.
(*3) chemical recycling
A recycling method in which used resources are chemically treated and converted into other chemical substances for reuse. In this case, it means converting used plastics into raw materials before manufacturing (synthesis).
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