New approaches enable chemical upcycling of polyethylene and polypropylene plastics

In two studies, researchers present new ways to convert common waste plastics, polyethylene (PE) and polypropylene (PP), into high-value chemical products, including alcohols, aldehydes, surfactants, and detergents. The approaches provide a pathway toward creating a circular plastics economy and the ability to produce high-value chemicals more sustainably. Waste plastics are increasingly being considered a potentially abundant source of feedstock to produce valuable chemical compounds. However, some plastics, particularly polyolefin plastics like PE and PP – widely used commodity plastics that account for nearly 60% of the world’s plastic production – are notoriously difficult to break back down into their original monomers. In one study, Houqian Li and colleagues demonstrate how waste polyolefin plastics can be converted into olefins via thermal depolymerization reactions such as pyrolysis. Traditionally, olefins are produced using energy-intensive methods and fossil fuel feedstocks such as natural gas and crude oil. Here, Li et al. show that the olefin mixtures produced by the pyrolysis of waste PE plastic can be converted into aldehydes, which can be reduced further into high-value oxygenated chemicals, including alcohols and diols. In another study, Zhen Xu and colleagues report a method for transforming PE and PP plastics into fatty acids, which can be converted further into highly valuable and commercially important surfactants and detergents. By controlling temperatures precisely during heating of polyolefin plastics, Xu et al. show that violent pyrolysis reactions, vaporization, and complete degradation to small molecules through difficult to control free-radical chemistry can be avoided, producing waxes. According to the authors, these waxes can be transformed into fatty acids through oxidation and saponification, which can be used to produce high-value surfactants. In a related Perspective, Kevin Van Geem highlights these methods and discusses how they could help close the loop on a circular plastics economy.

For reporters interested in trends, a July 2021 Special Issue of Science highlighted the rapidly growing plastic pollution problem and included a Review that focused on how innovation in plastic recycling and polymer upcycling could help promote closed-loop plastic recycling.