Washington DC [US], September 21 (ANI): Scientists at Oak Ridge National Laboratory have developed a relatively simple method to convert polyethylene, the widely used plastic found in shopping bags and cutting boards, into gasoline- and diesel-like fuels.
The process uses inexpensive aluminum-based molten salts to break down the plastic’s long molecular chains into smaller hydrocarbons, yielding around 60% gasoline under relatively mild conditions.
According to the ScienceDaily website, 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 aluminium 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, reported the ScienceDaily website.
Additional experiments using isotopic labelling 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, as quoted in ScienceDaily website.
“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,” added Zhenzhen.
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.
According to ScienceDaily website, 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 labelling 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 per cent 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.”
Tracking the Chemistry Atom by Atom
At ORNL, Luke Daemen used neutron scattering to help identify the hydrocarbon products created when different polymer chains reacted. Felipe Polo-Garzon analyzed the products with gas chromatography-mass spectrometry, a technique used to separate and identify individual chemical compounds.
When polyethylene interacted with an aluminum catalytic site, the reaction produced a positively charged carbon ion. Qiu, Yang and Dai tagged that carbon ion with deuterium, an isotope of hydrogen, allowing them to follow what happened to it as the reaction progressed.
The team also used neutrons at ORNL’s Spallation Neutron Source to monitor hydrogen within the system.
“The polymer contains a lot of hydrogen,” Dai said. “Neutrons are ideal at discerning light elements including hydrogen and its isotopes, such as deuterium.”
Researchers also needed to determine how the aluminium sites themselves changed during the process.
Yang travelled to the Advanced Light Source at Lawrence Berkeley National Laboratory, where she worked with Min-Jae Kim and Jinhua Guo. Using soft X-rays, the researchers examined interactions between aluminum and polyethylene at both the atomic and electronic levels. Soft X-rays are especially useful for studying relatively lightweight elements such as aluminum, as per ScienceDaily website.
“The aluminum edge shifted to the low-electron-density edge, which means some electron-rich intermediates formed,” Yang said.
“We compared the findings with other techniques and confirmed an aromatic ring intermediate can coordinate with aluminum and cause a binding-energy change,” added Yang.
That shift provided evidence that the aluminum sites were actively catalyzing the chemical reaction.
Simulations and Advanced Imaging Reveal the Mechanism
Back at ORNL, Bobby Sumpter of the Center for Nanophase Materials Sciences used computer simulations to study the energy changes taking place during the reaction, including how stable carbon ions formed and were transferred into hydrocarbon products.
At UTK, Michael Koehler used in situ X-ray diffraction to follow changes in the phases of the reaction mixture as the chemistry unfolded. Carlos Alberto Steren used nuclear magnetic resonance to investigate the aluminum catalytic sites.
ORNL’s Tao Wang contributed expertise in molten salt chemistry, while ORNL’s Logan Kearney supplied high-density polymers and provided expert guidance on possible routes for converting them into higher-value products.
A Remaining Challenge: Keeping the Salts Stable
Although the aluminum-based catalytic system is inexpensive and chemically active, it has an important limitation. The material is hygroscopic, meaning it readily absorbs water. That moisture can reduce its stability.
The researchers now want to investigate ways to confine the molten salts, potentially using halogens or carbon-based materials, which could make the salts easier to separate and process while improving their stability. (ANI)
