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It is well known that there are many potential valuable raw materials in used masks, shopping bags and food packaging, but the recycling and remanufacturing processes are usually energy-intensive and costly. Now, however, a new process is reported to produce fuel quickly at not too high temperatures and with few byproducts.

Normally, recycling plastics requires "cracking" or splitting the tough and stable chemical bonds that are the reason why plastics can persist so long in the environment. This cracking step requires high temperatures, high costs and energy intensive.

The latest process developed by the Pacific Northwest National Laboratory (PNNL) of the U.S. Department of Energy is different. Its novelty is that the cracking step can be combined with a second chemical reaction step (using an alkylation catalyst) to immediately complete the conversion to liquid gasoline-like fuel without unwanted byproducts.

The researchers pointed out that it was crucial in the current study that the alkylation reaction occurred immediately after the cracking step in a single reaction vessel at nearly 70 degrees Celsius. Their research results have been recently published in the journal Science.

"Previous processes simply broke chemical bonds, which causes them to form another bond in an uncontrolled way, and that's the problem," said Oliver Y. Gutiérrez, a chemist at PNNL and the study's author. "The secret here is that when you break one bond in our system, you immediately and specifically make another bond, giving you the final product you want. That's also the secret to achieving this transformation at low temperatures."

The fact that industry has successfully deployed these emerging alkylation catalysts is a testament to their stable, robust nature, said Johannes Lercher, senior author of the study and director of PNNL's Integrated Catalysis Institute. "This research points to a practical new solution to closing the carbon cycle for waste plastics, closer to implementation than many other proposals."

However, the new process currently has some limitations. The researchers say it works on low-density polyethylene products (LDPE), such as plastic films and squeezable bottles, and polypropylene products (PP), which are not typically collected in U.S. curbside recycling programs. In addition, high-density polyethylene (HPDE) requires pretreatment to allow the catalyst to invade the chemical bonds it needs to crack.