High performance catalyst that dissolves polyester and achieves chemical recycling

Professor Kotohiro Nomura’s research group at Tokyo Metropolitan University has developed two high-performance catalysts for efficient synthesis of value-added chemicals (fine chemicals, monomers) from polyester(1) and vegetable oil(2). Their main discovery is that the simple heating of a mixture of polyester and alcohol could make it possible to obtain exclusively raw materials.

Plastic waste is a huge environmental problem that needs to be solved immediately, but the amount of plastic reused (material recycling) is still small, especially chemically recycled into raw materials (called chemical recycling).(3)) is currently extremely low. Polyesters, made up of repeated “ester bonds”(1) formed by the reaction of carboxylic acid and alcohol, is used in plastic bottles and clothing. If these ester bonds could be completely broken, the polyester could be converted back into its raw materials. However, conventional processes require high temperatures and large amounts of acidic and/or basic materials. Therefore, a simple, inexpensive and environmentally friendly method is desired.

The research group has developed catalysts to facilitate the synthesis of high value chemicals (i.e. an oxide catalyst and a titanium catalyst. These catalysts are effective in breaking down polyester based on the same chemical reaction ( transesterification) and have been shown to be able to convert polyester into raw materials with nearly 100% selectivity.(4)

Calcium oxide, cheap and easy to acquire, has proven itself in industrial applications. However, the idea of ​​this research group to apply a catalyst used to convert vegetable oil esters directly as a polyester cracking catalyst is unprecedented in the research literature. In addition, its implementation is inexpensive with a low environmental impact. Moreover, because these titanium catalysts with their excellent catalytic performance have enabled a wide range of applications, strongly suggesting promise in the synthesis of polymeric materials and various fine chemicals from vegetable oil, as well as the upcycling(5) from plastic waste to high added value chemicals.

This research was conducted under the auspices of JST’s Strategic Basic Research Programs and Strategic International Collaborative Research Program (SICORP). The research involving the calcium oxide catalyst was conducted in collaboration with Prof. Boonyarach and Prof. Kitiyanan from Petroleum and Petrochemical College, Chulalongkorn University, Thailand. Both are Thai co-researchers of a joint international research project at SICORP, which is supported by both JST and the National Science and Technology Development Agency of Thailand (NSTDA).

The joint research paper is: “CaO Catalyzed Transesterification of Ethyl 10-Undecenoate as a Model Reaction for Efficient Conversion of Plant Oils and Their Application to Depolymerization of Aliphatic Polyesters,” ACS Sustainable Chemistry & Engineering. Published online, September 15, 2022, Doi: 10.1021/acssuschemeng.2c04287

(1) Polyester, ester linkages

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 from repeating units of ester bonds is called a polyester.

(2) Vegetable Oil

Vegetable Oils are obtained by extracting and refining the lipids contained in plants. The main component of fats and oils is triglyceride, which is a three-carbon alcohol called “glycerin” and a carboxylic acid with a chain structure of several carbon atoms, collectively called “long-chain fatty acids”. linked by ester bonds. . Long chain fatty acids (saturated and unsaturated) are obtained by the decomposition of glycerides (ester exchange reaction and transesterification with alcohols).

(3) Chemical recycling

A method of recycling in which used resources are chemically treated and converted into other chemical substances for reuse. In this case, it involves transforming used plastics into raw materials before manufacturing (synthesis).

(4) Selectivity

The ratio of target compound to reacted substrate (raw material).

(5) Recycling

Recover waste or unused products that would otherwise have been discarded into new products. In this case, it means converting used plastics into chemicals with higher added value than the raw material.

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