The Delusion of Advanced Plastic Recycling Using Pyrolysis — ProPublica (Jun 2024) Article

[Michael Harrop]

https://www.propublica.org/article/delusion-advanced-chemical-plastic-recycling-pyrolysis

The plastics industry is heralding pyrolysis as nothing short of a miracle: The “advanced” type of recycling uses heat to break plastic all the way down to its molecular building blocks.

Given the high stakes of this moment, I set out to understand exactly what the world is getting out of this recycling technology. For months, I tracked press releases, interviewed experts, tried to buy plastic made via pyrolysis and learned more than I ever wanted to know about the science of recycled molecules.

Under all the math and engineering, I found an inconvenient truth: Not much is being recycled at all, nor is pyrolysis capable of curbing the plastic crisis.

Not now. Maybe not ever.

Click to shrink...

Lesson 1
Most of the old plastic that goes into pyrolysis doesn’t actually become new plastic.

Lesson 2
The plastic that comes out of pyrolysis contains very little recycled material.

Lesson 3
The industry uses mathematical acrobatics to make pyrolysis look like a success.

Click to shrink...

At best, the world could replace 0.2% of new plastic churned out in a year with products made through pyrolysis.

Click to shrink...

 

[Michael Harrop]

There is a new article about a different method of chemical recycling that seems more promising:

‘Chemical recycling’: 15-minute reaction turns old clothes into useful molecules. Fast fashion creates millions of tonnes of waste each year — could clever chemistry help to tackle the problem? (Jul 2024) https://www.nature.com/articles/d41586-024-02210-1?

Researchers have developed a chemical-processing technique that can break down fabrics into reusable molecules, even when they contain a mixture of materials.

They used a chemical reaction called microwave-assisted glycolysis, which can break up large chains of molecules — polymers — into smaller units, with the help of heat and a catalyst. They used this to process fabrics with different compositions, including 100% polyester and 50/50 polycotton, which is made up of polyester and cotton.

For pure polyester fabric, the reaction converted 90% of the polyester into a molecule called BHET, which can be directly recycled to create more polyester textiles. The researchers found that the reaction didn’t affect cotton, so in polyester–cotton fabrics, it was possible to both break down the polyester and recover the cotton. Crucially, the team was able to optimise the reaction conditions so that the process took just 15 minutes, making it extremely cost-effective.

Click to shrink...

Chemical recycling of mixed textile waste (Jul 2024) https://www.science.org/doi/10.1126/sciadv.ado6827

Abstract​

Globally, less than 0.5% of postconsumer textile waste is recycled, with the majority incinerated or ending up in landfills. Most postconsumer textiles are mixed fibers, complicating mechanical recycling due to material blends and contaminants.

Here, we demonstrate the chemical conversion of postconsumer mixed textile waste using microwave-assisted glycolysis over a ZnO catalyst followed by solvent dissolution. This approach electrifies the process heat while allowing rapid depolymerization of polyester and spandex to their monomers in 15 minutes. A simple solvent dissolution enables the separation of cotton and nylon. We assess the quality of all components through extensive material characterization, discuss their potential for sustainable recycling, and provide a techno-economic analysis of the economic feasibility of the process.

Click to shrink...