Learn why stirring is one big innovation for a more sustainable future of chemical plastic recycling.
The Stirring Solution
Plastic residues have become a global problem, with hundreds of millions of tons being produced every year. New recycling methods are being developed around the clock and one of these up-and-coming solutions is chemical recycling.
As opposed to classical mechanical recycling — where each cycle can result in quality degradation — chemical recycling de-polymerises the plastic molecules into their basic constituents (monomers). From there, the monomers created can be pieced back together to create a new, virgin-quality plastic in a truly cyclical fashion.
The solution that unlocks the near-full potential of chemical recycling is mixing an obvious element. Scientists at ETH Zurich have found that the liquid plastic agitates during recycling is more than enough to determine how well and how fast you can recycle everything.
The Art of Stirring
Chemical recycling converts the molten plastic which is very viscous to a near crystal-like state when it comes out of the extruder heads. This poses a major challenge for optimal mixing of the catalyst powder and hydrogen into the mixture. Otherwise, if stirring is not proper then chemical reactions will not be as efficient and there may be formation of byproducts due to uneven distribution.
Earlier studies did not provide detailed information on mixing techniques, but researchers from ETH Zurich found that an axial blade impeller was the most beneficial stirring method to use. This design guarantees less flow vortices and a more homogeneous mixing much better than that obtained with typical angled blades or turbine-shaped stirrers.
However, the velocity of the stirrer is equally important. It should be neither too slow nor too fast but it needs to be around 1000 revolutions per minute. The researchers carefully modulated the stirring speed and geometry to develop a mathematical model characteristic of the complete chemical recycling process-kinetics concerning almost all parameters involved in it.
It marks a breakthrough for the chemical recycling sector, providing researchers with a new formula to estimate how changes to stirrer design and speed impact the PBH process efficiency. This paves the way for future experiments to be designed and aimed at conflating two different catalyst performances directly, now that mixing is managed.
Conclusion
Developers have not tested the recycling of the material, but the researchers at ETH Zurich believe they can use it to change plastic chemical recycling. They have effectively opened the door of stirring olefins, paving the way for a more reasonable and efficient recycling process that can transform plastic waste into good quality goods. In the years to come, as the scientific community hunts for even better catalysts and further develops the ideal chemical recycling technique, this finding could ultimately help lead us towards an actual circular economy in which plastic waste becomes a valuable instead of burdensome resource.
