Chemo-biological process overcomes drawbacks of waste plastic pyrolysis

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A joint research team has developed a technology to produce high-value-added plastic raw materials called dicarboxylic acids (α,ω-diacids) by recycling mixed waste plastics. The work is published in the Journal of Cleaner Production.

The team was led by Dr. Sang-Goo Jeon from the Bioenergy and Resources Upcycling Research Laboratory at the Korea Institute of Energy Research (KIER) and Dr. Jung-Oh Ahn from the BioProcess Engineering Center at the Korea Research Institute of Bioscience and Biotechnology (KRIBB)

Plastics are produced from fossil fuels like petroleum and natural gas, and waste plastics are recycled by shredding and melting them to make new products. However, during the production and processing stages, wastewater and harmful substances are released, causing serious environmental impacts.

To address these problems, many countries and companies are striving to establish a plastic circular economy. In particular, technologies that recycle plastics in an environmentally friendly manner through chemical methods such as pyrolysis are gaining attention recently.

However, the pyrolysis method is not a perfect solution either. This is because only 30% of the naphtha component in the pyrolysis oil produced during pyrolysis is recycled as raw material for plastics, while the majority is utilized as low-grade fuel that emits greenhouse gases during combustion.

The Korean research team proposed a chemo-biological process that combines chemical and biological methods to overcome the limitations of traditional chemical recycling techniques. Instead of using pyrolysis oil as a low-grade fuel, the developed process purifies it into normal paraffins which serve as raw materials for microbial reactions and utilizes them as feedstock for microorganisms to produce plastic raw materials.

By utilizing the chemical pretreatment technology developed by the Korea Institute of Energy Research (KIER), it is possible to selectively purify only normal paraffins from pyrolysis oil. When the pyrolysis oil reacts with a catalyst in a high-temperature environment at 400°C filled with hydrogen, impurities and toxic substances are removed, converting it into normal paraffins.

After the purified normal paraffins are utilized as food for microorganisms, they are ultimately converted into dicarboxylic acids—high-value-added plastic raw materials used in products like polyester (PES), polyamide (PA), and polyurethane (PU).

The research team predicted that utilizing this technology could reduce the production cost of plastic raw materials by up to 40% compared to existing petrochemical-based production technologies. Additionally, by recycling 30% of the pyrolysis oil that is typically used as low-grade fuel into plastic raw materials, it offers advantages for national greenhouse gas reduction.

Dr. Jeon stated, "This technology overcomes the limitations of existing chemical plastic recycling methods and is an achievement that can greatly contribute to establishing a plastic circular economy and realizing carbon neutrality. We are currently conducting verification procedures for synthesizing plastics using the dicarboxylic acids produced, and we plan to pursue technology transfer and commercialization through collaboration with interested companies."

More information: In-Seok Yeo et al, Integrating chemical and biological technologies in upcycling plastic waste to medium-chain α,ω-Diacid, Journal of Cleaner Production (2024). DOI: 10.1016/j.jclepro.2024.141890

Journal information: Journal of Cleaner Production

Provided by National Research Council of Science and Technology