< (From left) Kyeongmin Choi (MS-Ph.D. integrated course, Department of Chemistry), Dr. Beomsoon Park, Professor Soonhyuk Hong, Dr. Kyeongil Cho >
Billions of tires are discarded globally every year, and this is identified as one of the major causes of serious environmental pollution. The research team at KAIST Department of Chemistry has succeeded in selectively converting waste tires into high-purity cyclic alkenes, which are high-value chemical raw materials used as raw materials for rubber or nylon fibers. This is evaluated as a new turning point in the field of waste tire recycling.
Professor Soonhyuk Hong's research team from the Department of Chemistry at KAIST announced on June 26th that they have effectively solved the waste tire problem by developing a dual-catalyst-based continuous reaction system.
Waste tires are composed of a complex of synthetic and natural rubber, and their physical strength and durability are maximized by including additives such as silica, carbon black, and antioxidants. In particular, cross-linking between rubber chains is formed through the vulcanization process, giving them a structure resistant to heat and pressure, which is one of the main reasons why chemical recycling of waste tires is difficult.
Until now, waste tire recycling has mainly relied on pyrolysis or physical crushing recycling methods. The pyrolysis method is a technology that decomposes polymer chains at high temperatures of 350-800°C to convert them into fuel oil, but it clearly has limitations such as high energy consumption, low selectivity, and the production of low-quality hydrocarbon mixtures.
To solve these problems, the research team developed a method to convert waste rubber into useful chemicals using two catalysts. The first catalyst helps to break down rubber molecules by changing their bonding structure, and the second catalyst creates cyclic compounds through a ring-closing reaction.
This process shows high selectivity of up to 92% and a yield of 82%. The produced cyclopentene can be recycled back into rubber, and cyclohexene can be used as a raw material for nylon fibers, making them industrially very valuable.
The research team successfully applied the developed system to actual discarded waste tires, achieving selective conversion into high-purity cyclic alkenes. Unlike the existing pyrolysis method, this is evaluated as a new turning point in the field of waste tire recycling as it can produce high-value chemical raw materials through low-temperature precision catalytic reactions.
Furthermore, this technology can be widely applied to various types of synthetic rubber and waste rubber, drawing attention as a key original technology that can contribute to the realization of a resource-circulating economy.
< Figure 1. Development of a Catalytic Method for Chemical Recycling of Waste Rubber >
Professor Soonhyuk Hong stated, "This research presents an innovative solution for the chemical recycling of waste tires, and we plan to develop next-generation high-efficiency catalysts and establish a foundation for commercialization to enhance economic viability," continuing to say, "Our goal is to contribute to solving the waste plastic problem through basic chemistry."
This research, in which Beomsoon Park, Kyoungil Cho, and Kyungmin Choi of KAIST Department of Chemistry participated, was supported by the National Research Foundation of Korea and was published online in the internationally renowned academic journal 'Chem' on June 18th.
※Paper Title: Catalytic and Selective Chemical Recycling of Post-Consumer Rubbers into Cycloalkenes
※DOI: 10.1016/j.chempr.2025.102625
