High Molecular Weight Product Formation in Polyolefin Chemical Recycling: A Comprehensive Review on Primary and Secondary Products

Annually, an enormous amount of plastic waste is produced worldwide. This waste should be appropriately managed to limit the environmental burden. However, only a small part of plastic waste is recycled; the rest is burned, is disposed of, or ends up in the environment. In the transition toward a circular economy, chemical recycling has emerged as a promising conversion technique. Much of the research in chemical recycling focuses on producing lightweight liquids and gases. However, it is crucial to emphasize that valuable heavy products, such as waxes and lubricants, can also be obtained through upcycling. This perspective examines the chemical upcycling of polyolefin plastics into high molecular weight products, primarily focusing on waxes and lubricants. The production of heavy fractions from polyolefin plastics has the potential to be a profitable conversion strategy as value-added products are obtained. Favorable life cycle assessments prove it to be a sustainable strategy. Literature shows that different techniques, such as metathesis and hydrogenolysis catalysis or thermal pyrolysis, can be used to obtain heavy fractions from polyolefin plastics. Among these methods, thermal pyrolysis has been the subject of extensive research and is the most mature technology today. Additional chemical reactions can be used to further fine-tune the desired compositional or product properties, to clean the pyrolysis products, or to obtain other secondary products such as fuels and light olefinic gases.