Hard-to-recycle thermoset waste plastics reborn as hydrogen

A research team has successfully developed the Republic of Korea’s first continuous oxy-fuel combustion-based process for producing high-quality syngas from waste plastics, including hard-to-recycle thermoset resins. The team was led by Dr. Chong-Pyo Cho from the Energy Convergence System Research Department at the Korea Institute of Energy Research (KIER).

With the global climate crisis and resource depletion emerging as pressing issues, plastic waste recycling technologies are drawing increasing attention. As a result, the global waste plastic recycling market, valued at approximately 100 trillion KRW in 2023, is projected to grow at an average annual rate of 8.1%, reaching 173 trillion KRW by 2030.

Plastics are generally categorized into two types: thermoplastics, which can be reshaped when heated, and thermoset plastics, which become hard after curing and are difficult to decompose. Among these, thermoset plastics are known for their high heat resistance and chemical stability, making them useful in composite forms for automotive and electronic applications.

However, due to their decomposition requiring extremely high temperatures, they are often disposed of through landfilling or incineration after use, making them a major contributor to environmental pollution.

Dr. Chong-pyo Cho and his research team at the Korea Institute of Energy Research have developed an oxy-fuel combustion-based gasification process that converts mixed thermoset waste plastics into syngas, a key feedstock for hydrogen production.

For the first time in Korea, the team established a continuous process, improving process efficiency and successfully reducing tar, a byproduct of gasification, by 93.4% compared to the level typically required for commercial-grade syngas.

The research team implemented an oxy-fuel combustion control technology that removes nitrogen from air to minimize heat loss, along with a regenerative melting furnace system that retains heat within the gasifier. These innovations enabled the maintenance of high temperatures reaching 1,300°C. As a result, they established a continuous process from feedstock input through pretreatment to gasification, significantly maximizing overall process efficiency.

The amount of tar generated during the process was also drastically reduced. Tar, a byproduct of the process, has high viscosity and tends to stick to the process lines, hindering continuous operation.

Effective decomposition of tar requires temperatures above 1,000°C, but conventional plastic waste processing typically operates below 800°C, resulting in large amounts of undecomposed tar. While separate purification systems can be installed to remove tar, they significantly increase the overall process cost.

By maintaining high temperatures continuously through the integrated process, the research team succeeded in reducing tar generation to just 0.66 mg/Nm³ (milligrams per normal cubic meter) without the need for a separate purification system. This represents a 93.4% reduction compared to the tar concentration threshold required for syngas used in chemical fuel synthesis processes.

The developed process was demonstrated using a pilot plant capable of processing one ton of mixed thermoset waste plastics per day. The system showed a hydrogen production capacity of 0.13 kg per 1 kg of mixed waste plastics. Based on these results, the research team secured three domestic patents and filed one international patent, laying the foundation for commercialization.

Dr. Chong-pyo Cho, the lead researcher, stated, “This achievement is significant in that it greatly improves gasification efficiency and drastically reduces tar generation using entirely domestically developed technology. We plan to scale up the process to a capacity of 2 tons per day and continue related research to move toward commercialization.”