Researchers at the Department of Energy's Oak Ridge National Laboratory have developed a new way to transform polyethylene, one of the world's most common plastics, into gasoline- and diesel-like fuels. Polyethylene is widely used in products such as shopping bags and white plastic cutting boards, and large amounts of it ultimately end up as waste. The ORNL team's method combines the plastic with molten salts containing aluminum chloride.
These salts perform two jobs at once, acting as both the reaction medium and the catalyst that drives the chemical conversion. The researchers have applied for a patent for the technology, and the findings were published in the Journal of the American Chemical Society. How Molten Salts Break Plastic Into Fuel To understand why the process works, the scientists closely tracked the chemical reactions that convert the polymer into fuel molecules.
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. These sites can attack the long molecular chains that make up polyethylene and split them into smaller hydrocarbon molecules. Additional experiments using isotopic labeling and neutron scattering showed how the structure of the starting polymer influences the resulting fuel.
Simpler polymer chains tended to produce gasoline-like compounds, while more complex chains generated diesel-like fuels. If the method can eventually be scaled beyond laboratory experiments, the researchers say it could contribute to U.S. energy security and strengthen industrial competitiveness. "We developed an efficient and selective polyethylene-to-gasoline conversion," said Liqi Qiu, a postdoctoral researcher at the University of Tennessee, Knoxville, who performed most of the study's experiments in the ORNL laboratory of Sheng Dai, of ORNL and UTK.
Dai, an ORNL Corporate Fellow and section head for separations and polymer chemistry, is a co-corresponding author of the paper. The experiments achieved a gasoline yield of about 60 percent under relatively mild reaction conditions. Plastic-to-Gasoline Conversion Below 200 Degrees Celsius One of the most notable features of the method is how little it requires compared with more conventional plastic-to-fuel technologies.
"We converted polymer waste to value-added fuels by using commercially available inorganic salts as the reaction media to provide the catalytic sites," said Zhenzhen Yang, an ORNL staff scientist who was also a co-corresponding author of the paper. "Unlike traditional techniques for converting polymer to fuel, the new process did not require noble-metal catalysts, organic solvents or external hydrogen. This is the first time molten salts were used as media to produce high-value-added chemicals from waste without any catalytic initiator or solvent and at a temperature below 200 degrees Celsius." Temperatures below 200 degrees Celsius are comparable to those found inside a conventional kitchen oven.
Extract — continue reading at the source.
