Oak Ridge National Laboratory Team Turns Polyethylene Waste into Fuel Using Aluminum-Based Molten Salts

Key facts

• Researchers at the Department of Energy's Oak Ridge National Laboratory (ORNL) developed a method to transform polyethylene, one of the world's most common plastics used in shopping bags and white cutting boards, into gasoline- and diesel-like fuels.
• The ORNL team's method combines the plastic with molten salts containing aluminum chloride, which act as both the reaction medium and the catalyst driving the chemical conversion.
• The experiments achieved a gasoline yield of about 60 percent under relatively mild reaction conditions.
• Unlike traditional techniques, the process did not require noble-metal catalysts, organic solvents, external hydrogen, or a catalytic initiator, and is the first time molten salts were used to produce high-value-added chemicals from waste at a temperature below 200 degrees Celsius.
• Using soft X-ray spectroscopy and nuclear magnetic resonance, the team found that charged aluminum atoms bind with three other atoms, creating highly acidic catalytic sites that split polyethylene's long molecular chains into smaller hydrocarbons; simpler polymer chains produced gasoline-like compounds while more complex chains generated diesel-like fuels.
• The team also used neutrons at ORNL's Spallation Neutron Source to monitor hydrogen within the system, as neutrons are ideal at discerning light elements including hydrogen and its isotopes such as deuterium.
• The researchers have applied for a patent for the technology, and the findings were published in the Journal of the American Chemical Society.
• A key limitation is that the aluminum-based material is hygroscopic, readily absorbing water that reduces its stability; researchers want to investigate confining the molten salts, potentially using halogens or carbon-based materials, to improve stability.