How does pyrolysis contribute to chemical recycling of plastics?

Pyrolysis is a thermal decomposition process that plays a significant role in the chemical recycling of plastics. It involves heating plastic waste in the absence of oxygen at high temperatures, typically between 300°C and 900°C. This intense heat causes the long polymer chains to break down into smaller molecules, such as a mixture of gases, liquids (oil), and solid residue (char). The specific composition of the products depends on several factors, including the type of plastic, the temperature, the heating rate, and the presence of catalysts. The liquid oil fraction, often referred to as pyrolysis oil, is a complex mixture of hydrocarbons that can be further refined and processed into fuels, chemical feedstocks, or monomers for producing new plastics. The gaseous fraction can be used as a fuel to provide heat for the pyrolysis process itself, reducing energy consumption. The solid char residue can be used as a soil amendment or as a filler in other materials. Pyrolysis is particularly useful for recycling mixed plastic waste and plastics that are difficult to recycle mechanically, such as contaminated plastics. While pyrolysis offers a promising route for plastic recycling, it also presents challenges, including the need for efficient separation and purification of the pyrolysis oil, the management of gaseous emissions, and the optimization of the process to maximize the yield of valuable products. For example, pyrolysis can be used to break down polyethylene (PE) into a mixture of alkanes and alkenes, which can then be used to produce new PE or other chemicals.