Chemical Plastics Recycling

 


Researchers are working on new ways to recycle plastic waste. Methods include ways to turn waste into high- quality products, enabling a genuine circular economy. 

Currently, most plastic waste is recycled mechanically. It is shredded and then melted down. This method results in more plastic products, but their quality is degenerated with each recycling step. 

Chemical recycling is a new method being introduced. It avoids the big drop in quality. The technique involves breaking down long-chain plastic molecules (polymers).  They are formed into fundamental building blocks (monomers). These monomers can be re-created into new high-quality plastics. This is a sustainable cycle! 

The initial methods of chemical recycling focused on breaking down polymer chains into usable products like liquid fuels or even lubricants.  Plastic waste then has a new life as engine oil or jet fuel. 

Researchers at ETH Zürich have made important discoveries about these new techniques. The goal is to engage in more localized and effective recycling. 

The scientists were led by a professor of catalyst engineering named Javier Perez-Ramirez. He researched how to break down polyethylene and polypropylene with hydrogen. 

They begin by melting the plastic in a large steel tank. The hydrogen is then introduced into the softened plastic.  

This research was recently recently published in Nature Chemical Engineering. 

The next step is critical. It involves adding a powdered catalyst. Scientists can increase the efficiency of the chemical reaction with the addition. The catalyst increases the formation of molecules with separate chain length and at the same time decreases methane or propane by-products. 

Antonio Jose Martin is a researcher in the Perez-Ramirez group. He states, “ The molten plastic is 1000 times thicker than honey. The key is how you stir in the tank to ensure the catalyst powder and hydrogen get mixed right through.” 

The research team discovered that the molten plastic is best stirred by using an impeller with blades parallel to the axis. Also discovered is that stirring speed is crucial, the perfect speed is approximately 1000 revolutions per minute. 

The scientists developed a mathematical theorem to describe the chemical recycling process. 

Perez-Ramirez reports, “ It’s every chemical engineer’s  dream to have a formula like this at hand for their process.” 

With this new formula, researchers can directly compare different catalysts for with the impact of mixing under control.

The hope is to move from the laboratory to large scale recycling plants! 

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