A new method to convert low-density plastic waste to fuel and raw materials promises to help close the carbon cycle. Credit: Art by Melanie Hess-Robinson | Pacific Northwest National Laboratory
There's a lot of potentially useful raw materials bound up in used face masks, grocery bags and food wrap. But it has been much cheaper to keep making more of these single-use plastics than to recover and recycle them.
Now, an international research team led by the Department of Energy's Pacific Northwest National Laboratory has cracked the code that stymied previous attempts to break down these persistent plastics. They reported their discovery in today's issue of Science (Feb. 23).
Low temperature and reaction control
Typically, recycling plastics requires "cracking" or splitting apart the tough and stable bonds that also make them so persistent in the environment. This cracking step requires high temperatures, making it expensive and energy intensive.
The novelty here is combining the cracking step with a second reaction step that immediately completes the conversion to a liquid gasoline-like fuel without unwanted byproducts. The second reaction step involves what are known as alkylation catalysts. These catalysts provide a chemical reaction currently deployed by the petroleum industry to improve the octane rating of gasoline.
Crucially, in the current study, the alkylation reaction immediately follows the cracking step in a single reaction vessel, at near room temperature (70 degrees C/158 degrees F).