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New process could reduce cost of manufacturing plastic

By Allen Cone
New process could reduce cost of manufacturing plastic
A new filtering material that can separate purified ethylene out of ethane, could reduce the environmental cost of manufacturing plastic. Photo by kalhh/pixabay

Oct. 26 (UPI) -- Scientists have developed new filtering material that could reduce the environmental cost of manufacturing plastic by separating purified ethylene out of ethane.

By extracting the key ingredient in the most common form of plastic from a mixture of other chemicals, they believe their process consumes far less energy than other methods. The metal-organic framework developed by the National Institute of Standards and Technology was published Friday in the journal Science.

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The plastic and petroleum industries manufacture around 170 million tons of ethylene worldwide each year by pulling the material out of a mixture with ethane in the oil refining process.

For years, scientists have been searching for an alternative method to the current high-energy process that cools down the crude to more than 212 degrees below zero Fahrenheit.

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Industries would prefer to wring out ethylene, which is the molecule needed to create polyethylene used to make shopping bags and other everyday containers.

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"It's very difficult to do," Dr. Wei Zhou, a scientist at the NCNR, said in a press release. "Most MOFs that have been studied grab onto ethylene rather than ethane. A few of them have even demonstrated excellent separation performance, by selectively adsorbing the ethylene."

From an industrial perspective, they would prefer to do the opposite if feasible. "You want to absorb the ethane byproduct and let the ethylene pass through," he said.

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Under a microscope, the metal-organic framework looks like a half-built skyscraper of girders and no walls, according to the scientists. The girders surfaces contain certain hydrocarbon molecules that will stick to firmly. A mixture of two hydrocarbons poured through the right MOF can pull one kind of molecule out of the mix and allowing other hydrocarbon to emerge in pure form.

The scientists built their system at the University of Texas at San Antonio and China's Taiyuan University of Technology.

In 2012, other researchers at the NCNR found that a particular framework called MOF-74 separated a variety of hydrocarbons, including ethylene.

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"A huge topic in chemistry is finding ways to break the strong bond that forms between carbon and hydrogen," said team leader UTSA professor Banglin Chen. "Doing that allows you to create a lot of valuable new materials. We found previous research that showed that compounds containing iron peroxide could break that bond."

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To break the bond in a hydrocarbon molecule, the compound would first have to attract the molecule. By modifying MOF-74's walls to contain a structure similar to the compound, the molecule it attracted from their mixture was ethane.

By using neutron diffraction, they found what part of the MOF's surface attracts ethane.

"Without the fundamental understanding of the mechanism, no one would believe our results," Chen said. "We also think that we can try to add other small groups to the surface, maybe do other things. It's a whole new research direction and we're very excited."

The researchers said they need to further develop the process before it is adapted.

"We proved this route is promising, but we're not claiming our materials perform so well they can't be improved," Zhou said. "Our future goal is to dramatically increase their selectivity. It's worth pursuing further."

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