South Korean researchers have developed a method for hydrogen storage using polystyrene waste, turning plastic into liquid organic hydrogen carriers with dual benefits.
Hydrogen storage from plastic waste
A new strategy to achieve safe hydrogen storage is emerging from the world of waste. A team of engineers and chemists at the Ulsan National Institute of Science and Technology (UNIST) in South Korea has succeeded in converting discarded polystyrene into liquid organic hydrogen carriers (LOHC). The process could deliver a double benefit: offering a competitive low-cost system for transporting hydrogen and creating a new upcycling pathway for plastic waste.
The challenge of recycling polystyrene
Polystyrene, also known as expanded polystyrene (EPS), remains a significant environmental challenge at end of life. This thermoplastic polymer is widely used in packaging and building insulation and is highly resistant to degradation. In the absence of sunlight, EPS can persist in the environment for millennia, while full photochemical oxidation requires hundreds of years.
Post-consumer recycling of polystyrene is therefore essential, but in practice remains fraught with difficulties. Obstacles include large waste volumes, costly pre-treatment steps, and the low market value of recycled products, all of which undermine economic viability. In some conditions, recycled EPS also degrades, losing its key properties.
LOHC from styrene and toluene
The UNIST team, led by Professor Kwangjin An of the School of Energy and Chemical Engineering, designed a closed-loop system that converts polystyrene waste into liquid organic hydrogen carriers. These molecules store hydrogen within their cyclic chemical structures, allowing safe storage at ambient temperature and pressure.
The process leverages the aromatic composition of polystyrene. When heated, the polymer breaks down into low-molecular-weight aromatics such as styrene and toluene. At high temperatures, these compounds can react with hydrogen and bind it in a stable form. To release the hydrogen, catalytic dehydrogenation is applied.
Hydrogen storage and release with platinum catalysts
The researchers used platinum as a catalyst to facilitate hydrogen release, discovering that performance varied depending on the catalyst’s support structure.Platinum-based catalysts on alumina nanosheet assemblies demonstrated higher reactivity and stability, significantly improving reaction efficiency.
Challenges remain, however. Polycyclic compounds in the LOHC derived from polystyrene caused catalyst deactivation through coke formation. This was resolved by adding a distillation step to remove impurities. The team also optimized the process from an energy-economic perspective by recovering and reusing waste heat.
“The life-cycle assessment and techno-economic analysis confirmed that upcycling polystyrene waste into liquid organic hydrogen carriers provides both environmental advantages, including a negative carbon footprint for LOHC production, and economic sustainability through competitive transport costs,” the scientists explained.
Their findings were published in ACS Catalysis under the title Upcycling Post-Consumer Polystyrene Waste into Liquid Organic Hydrogen Carriers.
