US researchers discover new “industry-changing” advanced recycling method

(Image credit: Joel Hallberg).

14 Aug 2023 --- Chemical engineers at the University of Wisconsin-Madison, US, are turning low-value waste plastic into high-value products with a new recycling technique. 

The method, described in the journal Science, could increase the economic incentives for plastic recycling and introduce the recycling of new types of plastic. The researchers estimate their methods could also reduce GHG emissions from the conventional production of olefins  by 60%. 

The scientists assert that the recycling industry could adopt the process soon. In recent years, at least ten large chemical companies have built or announced plans for facilities to produce pyrolysis oils from waste plastics. 

The researchers explain that many plants run the pyrolysis oil through steam crackers to produce low-value compounds. The new chemical recycling technique could provide a more sustainable and lucrative way to use those oils.

A low-energy intense process
The technique relies on existing chemical processing techniques. The first is pyrolysis, in which plastics are heated to high temperatures in an oxygen-free environment. The result is pyrolysis oil, a liquid mix of various compounds. 

The scientists recover olefins from pyrolysis oil and use them in a low-energy-intensive chemical process.Pyrolysis oil contains large amounts of olefins – a class of simple hydrocarbons that are a central building block of chemicals and polymers, including polyesters, surfactants, alcohols and carboxylic acids.

In current energy-intensive processes like steam cracking, chemical manufacturers produce olefins by subjecting petroleum to extremely high heat and pressure. 

In the newly researched process, the scientists recover olefins from pyrolysis oil and use them in a low-energy-intensive chemical process called homogeneous hydroformylation catalysis. The process converts olefins into aldehydes, which can be further reduced into important industrial alcohols.

“These products can be used to make a wide range of materials that are of higher value,” says George Huber, the chemical and biological engineering professor who led the work alongside postdoctoral researcher Houqian Li and PhD student Jiayang Wu.

Building on existing technologies 
The higher-value materials include ingredients used to make polymers, soaps and cleaners.

“We’re excited about the implications of this technology,” says Huber, who also directs the University of Wisconsin-Madison’s Department of Energy-funded Center for the Chemical Upcycling of Waste Plastics. “It’s a platform technology to upgrade plastic waste using hydroformylation chemistry.”

“Currently, these companies don’t have a really good approach to upgrade the pyrolysis oil,” says Li. “In this case, we can get high-value alcohols worth US$1,200-US$6,000 per metric ton from waste plastics, which are only worth about US$100 per metric ton. In addition, this process uses existing technology and techniques. It’s relatively easy to scale up.”

The study was collaborative across several of the university’s departments, Huber says. The next step for the team is to tune the process and better understand what recycled plastics and catalyst combinations produce which final chemical products.

“There are so many different products and routes we can pursue with this platform technology,” says Huber. “There’s a huge market for the products we’re making. I think it really could change the plastic recycling industry.”

Edited by Natalie Schwertheim

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