Inspenet, March 15, 2023
Researchers at the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) have developed a new method for converting low-density plastic waste into fuel and raw materials. A solution that could close the carbon cycle. The team published the results of their discovery in the journal Science.
Recycling plastics typically requires “breaking” or separating the strong, stable bonds that also make them so persistent in the environment. This cracking step requires high temperatures, which makes it expensive, as well as consuming a lot of energy.
The new model combines the cracking step with a second reaction process that immediately completes the conversion to a gasoline-like liquid fuel without unwanted by-products. The second reaction step deploys what are known as alkylation catalysts.
These catalysts provide a chemical reaction currently used by the oil industry to improve the octane number of gasoline.
“Cracking just to break the bonds results in another one forming in an uncontrolled way, and that’s a problem in other approaches,” said Oliver Y. Gutierrez, study author and PNNL chemist. “The secret formula here is that when you break a link in our system, you immediately create another one in a specific way that gives you the final product you want. That is also the secret that allows this low-temperature conversion.”
In their study, the research team, co-led by scientists from the Technical University of Munich (TUM), Germany, noted that there are recent developments separate from the oil industry to commercialize the second part of the new recycling process.
“The fact that the industry has successfully implemented these emerging alkylation catalysts demonstrates their stable and robust nature,” said Johannes Lercher, lead author of the study, director of PNNL’s Institute for Integrated Catalysis and professor of chemistry at TUM. “This study points to a practical new solution to close the carbon loop for plastic waste that is closer to implementation than many other proposals.”
The researchers stressed that there is a limitation to their findings. The process works for Low Density Polyethylene (LDPE, plastic resin code #4) products, such as plastic films and squeeze bottles, and polypropylene (PP, plastic resin code #5) products that would not normally they are collected in recycling programs in the United States. In contrast, High Density Polyethylene (HPDE, plastic resin code #2) would require pretreatment to allow the catalyst access to the bonds it needs to break.
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