Impurities Hindering Waste Plastic Recycling Identified... AI Reveals Why [Reading Science]

KRICT, Korea University of Technology and Education Compare 13 Impurities in Pyrolysis Oil
Nitrogen-Containing Compounds Reduce Catalyst Performance... Findings Expected to Help Manage Feedstock Quality

The types of impurities that reduce production efficiency when recycling waste plastics into petrochemical feedstocks, and how they work, have been identified. In particular, some nitrogen-containing compounds were found to occupy active sites on catalysts, hindering the production of plastic feedstocks. The findings are expected to help assess the quality of waste plastic pyrolysis oil in advance and improve recycling process efficiency.

The Korea Research Institute of Chemical Technology (KRICT) said on November 9 that a research team led by Dr. Kim Dokyung, in collaboration with a team led by Professor Kim Taeyong of Korea University of Technology and Education, had identified how 13 impurities in waste plastic pyrolysis oil affect catalyst performance through experiments and AI-based computational chemistry.

Technology overview. Created using AI by a research team at the Korea Research Institute of Chemical Technology.

Waste plastic pyrolysis oil is oil obtained by breaking down discarded plastics at high temperatures. It can be used as a feedstock to replace petroleum or naphtha. When processed using a catalyst, it can produce light olefins, the basic feedstocks for plastics and chemical products, including ethylene and propylene.

The problem lies in the impurities in pyrolysis oil. Depending on the types of waste plastics and additives, nitrogen-, sulfur-, chlorine- and oxygen-containing compounds can be present. If these compounds interfere with the catalyst's reactions, production efficiency may decline. Differences in the types and concentrations of impurities in each feedstock also make stable process operation difficult.

In 2024, the research team developed a circulating fluidized-bed catalytic cracking technology that converts waste plastic pyrolysis oil into light olefins without separate hydrotreatment. In this study, the team extended that research to analyze how catalyst performance changes with variations in impurity composition.

Nitrogen-Based Impurities Disrupt Catalytic Reactions... AI Reveals Why

The team separately added 13 nitrogen-, sulfur-, chlorine- and oxygen-containing impurities to actual waste plastic pyrolysis oil, then compared the yield and product distribution of light olefins using a zeolite catalyst.

The results showed that sulfur-, chlorine- and oxygen-containing compounds had relatively small effects, while some nitrogen-containing compounds significantly reduced catalyst performance. The effect of the nitrogen-containing compound 2-methylpyridine was particularly strong, while that of benzonitrile was relatively small. This indicates that not only the total amount of nitrogen in pyrolysis oil but also the forms of nitrogen compounds it contains are important.

Analyzing the Catalytic Adsorption Properties of Nitrogen-Based Impurities Through AI-Based Computational Chemistry; Research Team Uses AI in Development

To identify the reasons for these differences, the research team used machine learning potentials (MLPs), an AI-based computational chemistry technique. The team compared how strongly nitrogen-containing compounds and hydrocarbons bind to active sites inside the catalyst.

Zeolite catalysts have active sites that break down hydrocarbons. If certain nitrogen-based impurities occupy these sites first, hydrocarbons have fewer opportunities to react, reducing light olefin production. The team also confirmed that molecular size and the space inside the catalyst affect performance degradation.

As the concentration of nitrogen-based impurities increased, catalyst performance declined further, but raising the reaction temperature mitigated the effect. Catalysts whose performance had declined through repeated use also recovered their initial performance after regeneration treatment to remove carbon deposits.

The research team (from left): Professor Kim Taeyong of Korea University of Technology and Education; Tran Ngan Ha, a student researcher at the University of Science and Technology (UST); postdoctoral researcher Won Geunhye; UST student researcher Ngo Thi Thanh Ngan; Principal Researcher Kim Dokyung of the Korea Research Institute of Chemical Technology; postdoctoral researcher Tran Xuan Tin; and postdoctoral researcher Jung Dongjae. Photo provided by the Korea Research Institute of Chemical Technology.

This study provides a scientific basis for assessing feedstock suitability by considering not only the total amount of impurities in waste plastic pyrolysis oil but also their types. The findings are expected to help optimize impurity management, pretreatment processes and catalyst operating conditions.

"Before feedstock is introduced into a process, analyzing its impurity composition can help estimate the risk of declining catalyst performance. We expect these findings to be used to develop impurity management and operating strategies suited to the characteristics of each feedstock," said Shin Seokmin, president of the Korea Research Institute of Chemical Technology.

The findings were published as a cover article in the April 2026 issue of the international journal ACS Catalysis.

This content was produced with the assistance of AI translation services.