Scientists Find a Way to Break Polyethylene Plastics To Create High-Value Feed Stocks That Can Reduce Usage of Fossil Fuels

Polyethylene plastics, which include single-use bags and general-purpose bottles, are indestructible forever.

This also makes them difficult to recycle.

However, chemists have discovered a mechanism to degrade the polymer (a chain of around a thousand ethylene molecules) into three-carbon propylene molecules, which are in great demand for the production of another plastic, polypropylene.

The process could convert waste plastic into high-value feedstocks, reducing the need for fossil fuels in the production of propylene.

The process converts polyethylene bags

(Photo : SANJAY KANOJIA/AFP via Getty Images)

The technique, which is still in its early phases, would convert a waste product - plastic bags and packaging and all forms of PE plastic bottles - into a major product in great demand, as per ScienceDaily.

Previous techniques for breaking polyethylene chains needed high temperatures and produced combinations of components in considerably lower demand.

The novel approach might not only reduce the demand for fossil fuel production of propylene, also known as propene but also assist address a currently unmet need for additional propylene in the plastics sector.

Many polyethylene polymers are recycled and converted into low-quality products.

"You can't take one plastic bag and make another with the same properties," according to John Hartwig, the Henry Rapoport Chair in Organic Chemistry at UC Berkeley.

However, if you can return the polymer bag to its monomers, break it down into little bits, and depolymerize it, instead of drawing additional carbon from the earth, you may utilize that as a carbon source to manufacture other things, such as polypropylene.

The scientists would utilize less shale gas for that reason, as well as for other propane uses, and to address the so-called propylene gap.

Polyethylene plastics account for almost one-third of the global plastics industry, with more than 100 million tons produced annually from fossil fuels, including natural gas derived by hydraulic fracturing, sometimes known as shale gas.

Despite recycling initiatives (recyclable polyethylene plastic items are labeled with plastic numbers 2 and 4), only around 14% of all polyethylene plastic products are recycled.

Because polyethylene polymers are difficult to depolymerize or break down into their component components due to their stability, the majority of recycling includes melting it and molding plastic into other goods such as yard furniture or burning it as fuel.

Also Read: Scientists Creates Enzyme that Breaks Down Plastics Turning Centuries of Degradation Into Days

two kinds of catalysts

Hartwig specializes in inserting uncommon and reactive bonds into hydrocarbon chains, the majority of which are petroleum-based.

To generate new materials, novel chemical groups can be added to these reactive bonds.

Because of its general non-reactivity, the hydrocarbon polyethylene, which normally exists in a polymer chain of 1,000 ethylene molecules (each ethylene is made of two carbon and four hydrogen atoms), presented a problem to his team.

With the assistance of a U.S. To research novel catalytic processes, Hartwig and graduate students Steven Hanna and Richard J. "RJ" Conk devised the notion of using a catalyst to break two carbon-hydrogen bonds on polyethylene, originally with an iridium catalyst and then with platinum-tin and platinum-zinc catalysts, to generate a reactive carbon-carbon double bond that would function as an Achilles' heel.

With this breach in the armor of the polymer's carbon-hydrogen bonds, they could next unwind the polymer chain using ethylene and two more cooperatively reacting catalysts.

"We take a saturated hydrocarbon - all carbon-carbon single bonds - and remove a few molecules of hydrogen from the polymer to generate carbon-carbon double bonds, which are more reactive than carbon-carbon single bonds," Hartwig explained.

The addition of a second palladium catalyst allowed propylene molecules (three-carbon molecules) to be repeatedly cut off the reactive end.

The end result was that 80% of the polyethylene was converted to propylene.

Why Convert Plastic to Fuel?

According to some studies, less than 5% of produced plastic gets recycled each year.

Researchers estimated that it would take more than 450 years for this plastic to biodegrade if it ever did, as per Plug and Play.

The facilities involved in the plastic-to-fuel transition have the potential to create up to 39,000 new employment and about $9 billion in economic activity.

This has the potential to boost our economy while simultaneously giving innovative methods to repurpose plastic and save the environment.

This new method may also be less expensive than current recycling methods.

Currently, it costs upwards of $4,000 to recycle one tonne of plastic bags; to avoid these high costs, many people burn plastic or dispose of it in landfill.

Chemical recycling is a lot easier. There is no need to pre-sort garbage when everything is heated to high temperatures.