A new technology turns waste plastics into valuable chemicals

Researchers transformed a plastic bag and bottle cap into a type of chemical used in pharmaceuticals, detergents, paints, and other products.

Charles Q. Choi, contributor

(Inside Science) – A novel technique can simultaneously break down the most commonly used form of plastic and synthesize valuable, widely used molecules, possibly by recycling some plastic waste and making it more attractive and Makes it practical, finds a new study.

Roughly 300 million metric tons of plastic waste is produced each year, with approximately 12 billion metric tons of such waste expected to pollute the planet by 2050. The molecule polyethylene, often used in packaging and grocery bags, is the largest component of plastic waste, and can decompose for many centuries, said senior author Susanna, a chemical engineer at the University of California, Santa Barbara Study Scott.

One problem with plastic is that it is cheap and easy to produce and has to be thrown away. Products made from recycled plastics often have inferior properties to new ones, and breaking plastics into their original building blocks is often complex and requires too much energy or chemicals, so the resulting product often costs processing costs. Do not retrieve

One possible way to address this economic barrier is to “upcycle” plastic waste – turning it into valuable chemicals. However, this often involves an energy-intensive, laborious step of breaking down the plastic to its original components before synthesizing the desired compounds.

Now Scott and his colleagues have developed a simple, low-energy technology to convert polyethylene into alkylaromatic compounds, the basis of many detergents, lubricants, paints, solvents, pharmaceuticals, and other industrial and consumer products, and are currently $ 9 billion support the market. . They successfully tested their method on real polyethylene waste made from plastic bags and water bottle caps.

“Polyethylene is one of the most used and produced plastics in the world – did not participate in this study, but wrote in a perspective,” said Bert Weckhuysen, a chemical engineer at the University of Utrecht in the Netherlands, who wrote a huge waste stream . ” Article on research for the journal. “They are able to convert a low-value product into a high-value product.”

Only moderate temperatures are required – while traditional methods for manufacturing alkylaromatics typically demand temperatures of 500 to 1,000 ° C (about 930 to 1,830 ° F), this new process simply requires about 300 ° C (approx. 570 ° F) is required. It also does not call for water or any other solvent – it simply requires polyethylene brewing with a common type of catalyst made of platinum nanoparticles on alumina grains, long used in oil refining.

This new strategy relies on two different chemical reactions that operate in tandem. One uses hydrogen to separate polyethylene into small pieces, breaking strong molecular bonds by holding the plastic together, while the other synthesizes alkaliotic compounds. The latter reaction produces hydrogen which can help drive the former reaction. Only small amounts of byproducts are produced – light gases such as methane, which can be lit to help provide energy to drive the process.

Scott said, “The most surprising is that polyethylene is actually a better starting point for making alkylaromatic molecules than the normal starting point, which is that the molecules come directly from the oil.” They reported that this new method of making alkylomatics requires much less heat than conventional methods.

“In this sense, plastic is not the best to use, but is actually preferred, and it gives a new way of looking at the value of plastic waste,” Scott said. “We are reminded that plastic is a highly engineered and processed material whose energy and chemical content represent a disadvantage rather than an opportunity to overcome.”

A drawback of this new technique is that the catalyst loses activity over time as the substance shines on it. However, Scott said that anyone can refresh it by, say, heating the catalyst in the presence of air to burn anything present on the surface.

Although the catalyst itself is expensive, “its cost is the huge amount of refinement of the product that it can produce over many years,” Scott said. Weckhuysen said future research could develop a cheaper alternative.

Future research could not only explore ways to make this catalyst more effective, but also examine various catalysts that can break down other plastics or produce other valuable products, Scott said. This can help lead to a future where plastic is not considered to be worthless, but rather a valuable raw material, Weckhuysen said.

Scientists detailed their findings in the October 23 issue of the journal Science.

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