Upcycling waste PET bottles into raw pharmaceutical materials

Joint study by professor Kyoung Heon Kim’s group with Ewha Womans University

Published in the December issue of American Chemical Society (ACS) Sustainable Chemistry and Engineering (IF:6.97)

▲ Professor Kyoung Heon Kim of the Korea University Division of Biotechnology (left, corresponding author) 

and Dr. Hee Taek Kim (right, first author).

A million plastic bottles are bought and eventually disposed of around the world every minute. In answer to this growing environmental crisis, a technology to upcycle PET bottles into raw materials of pharmaceuticals was developed.

The technology enables one to chemically degrade polyethylene terephthalate (PET), the main ingredient of most plastic bottles, and biologically convert it into useful materials. Professor Kyoung Heon Kim’s group in the Korea University Division of Biotechnology has developed technology to convert PET into the water materials of pharmaceuticals and plastic products through collaboration with Dr. Hee Taek Kim, Jeong Chan Joo, Hyun Gil Cha’s group at the Korea Research Institute of Chemical Technology and with Professor Si Jae Park’s group from Ewha Womans University.

The joint study team designed a strategy to degrade PET into monomers (unit molecules) by an environmentally friendly method using water and to convert the resulting monomers into useful materials by using microorganisms. First, PET is chemically degraded into terephthalic acid and ethylene glycol through a reaction with water in a microwave reactor at 230℃. The yield of the products was as high as 99.9%. The acquired terephthalic acid and ethylene glycol are then converted into useful materials by using microorganisms. The terephthalic acid is converted into gallic acid (92.5%), catechol (90.1%), pyrogallol (20.8%), muconic acid (85.4%) and vanillic acid (29.4%), and the ethylene glycol into glycolic acid (98.6%). Gallic, muconic, vanillic, and glycolic acids and pyrogallol are materials used as raw materials for pharmaceuticals, plastic products and aromatic chemicals. For example, gallic acid is used as an intermediate of a pharmaceutical (antioxidant), muconic acid as a plastic monomer and vanillic acid as an aromatic ingredient of pharmaceuticals and cosmetics.

Since PET can be converted into various materials, the newly developed technology may be used to improve the low productivity of the conventional PET recycling method, contributing to a reduction of PET waste. Conventional PET recycling involves mechanical and chemical methods. The mechanical methods include mechanical treatments, such as crushing, washing and drying, as well as thermal treatment to recover PET fibers for use in a new product. However, as the fiber length is shortened during the processing, the quality of the new products is lowered. The chemical methods include PET fiber degradation, monomer recovery and re-polymerization. However, the high cost of the chemical methods decreases the economic feasibility of this type of recycling.

The present study provides a step forward for acquiring raw materials for other products from plastic waste, which used to be considered only trash. More studies are expected to be conducted to upcycle plastic waste, including PET, to obtain useful resources and materials.

The results of this study were published in the December issue of ACS Sustainable Chemistry & Engineering (IF:6.97), an international journal published by the American Chemical Society (ACS). The study was supported by the Midcareer Researcher Program and the Korea Bio Grand Challenge Program from the National Research Foundation of Korea and the Korea CCS 2020 Program from the Ministry of Science, ICT & Future Planning.

*Title of Article: Biological Valorization of Poly(ethylene terephthalate) Monomers for Upcycling Waste PET (ACS Sustainable Chem. Eng. 2019, 7, 24, 19396-19406)

[Figure]

▲ The waste PET is chemically degraded into terephthalic acid and ethylene glycol. Then, a microorganism is used to convert the terephthalic acid, via protocatechuic acid as the key intermediate, into gallic acid, pyrogallol, catechol, muconic acid and vanillic acid. Ethylene glycol is converted into glycolic acid by using a strain that metabolizes ethylene glycol.