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New recycling process could find markets for plastic waste

New recycling process could find markets for plastic waste
Low-value waste plastic can be converted into high-value chemicals in a new process developed by UW–Madison researchers (photo courtesy Joel Hallberg).

Chemical engineering researchers at the University of Wisconsin–Madison in the United States are turning low-value waste plastic into high-value products. The new method could increase the economic incentives for plastic recycling and open a door to recycling new types of plastic as well as reduce greenhouse gas emissions from the conventional production of these industrial chemicals by roughly 60 percent.

Although many Americans dutifully deposit their plastic waste into the appropriate bins each week, many of those materials, including flexible films, multilayer materials, and a lot of colored plastics, are not recyclable using conventional mechanical recycling methods.

In the end, only about 9 percent of plastic in the United States is ever reused, often in low-value products.

With a new technique, however, University of Wisconsin–Madison chemical engineers are turning low-value waste plastic into high-value products.

The new method, described in the paper “Hydroformylation of pyrolysis oils to aldehydes and alcohols from polyolefin waste“, and recently published in the journalScience,可以增加塑料的经济激励ic recycling and open a door to recycling new types of plastic.

The researchers estimate their methods could also reduce greenhouse gas (GHG) emissions from the conventional production of these industrial chemicals by roughly 60 percent.

Build on existing processing technologies

The new technique relies on a couple of 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 including large amounts of olefins — a class of simple hydrocarbons that are a central building block of today’s chemicals and polymers, including various types of polyesters, surfactants, alcohols, and carboxylic acids.

Enter “homogenous hydroformylation catalysis”

Using a process called hydroformylation, Professor George Huber (left) and post-doctoral researcher Dr Houqian Li are able to recover the olefins in an oil made from waste plastic and transform them into high-value chemicals (photo courtesy Joel Hallberg).

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

In this new process, the UW–Madison team recovers olefins from pyrolysis oil and uses them in a much less energy-intensive chemical process called “homogenous hydroformylation catalysis”.

This process converts olefins into aldehydes, which can then be further reduced into important industrial alcohols.

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

These higher-value materials include ingredients used to make soaps and cleaners, as well as other more useful polymers.

Platform technology with potential

We’re really excited about the implications of this technology. It’s a platform technology to upgrade plastic waste using hydroformylation chemistry, said Professor George Huber, who also directs the US Department of Energy-funded Center for the Chemical Upcycling of Waste Plastics (CUWP).

TheCenter for the Chemical Upcycling of Waste Plasticsis a DOE-funded, multi-university center consisting of six universities, over twenty industrial partners, one industry association, and theNational Renewable Energy Laboratory(NREL).

Currently, there are limited options for cost-effective plastic waste recycling, and most generate a product with substantially lower value and quality than virgin plastic. This exciting new technology paves the way for truly sustainable plastics and a circular plastics economy, commented Dr Gayle Bentley, US Department of Energy (DOE)Bioenergy Technologies Office(BETO) Technology Manager for CUWP.

The recycling industry could adopt the process soon; in recent years, at least 10 large chemical companies have built or announced plans for facilities to produce pyrolysis oils from waste plastics.

Many of them 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.

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

Collaborative effort

The study itself was also a collaborative effort across a few different University of Wisconsin–Madison (UW–Madison) departments.

Clark Landis, Chair of the Department of Chemistry and a world expert on hydroformylation suggested the possibility of applying the technique to pyrolysis oils.

Chemical and biological engineering Professor Manos Mavrikakis used advanced modeling to provide molecular-level insight into the chemical processes, and chemical and biological engineering Professor Victor Zavala provided help analyzing the economics of the technique and the life cycle of the plastic waste.

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 so many routes we can pursue with this platform technology. There’s a huge market for the products we’re making. I think it really could change the plastic recycling industry, ended Professor George Huber.

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