Chemical Recycling of Plastics

The Chemical Recycling of Plastics can be split into three broad technology categories:

• Solvent Purification
• Chemical Depolymerisation
• Thermal Depolymerisation (also known as Catalytic depolymerisation, also known as thermal cracking and thermolysis)

Overview

The diagram below is reproduced from the same report and shows the potential application of the technologies to the plastics value chain:

Figure 1 of report by Eunomia for the Chem Trust on Chemical Recycling Technologies for plastics dated Dec 2020

Solvent Purification

The plastic is shredded and dissolved within a solvent that the polymer has high solubility in, but the contaminants have low solubility in. The contaminants will, therefore, remain solid and so can be separated off from the liquid fraction to purify the polymer. Once the purification process is complete, the polymer is extracted from the solution by placing in a non-solvent to re-solidify the polymer, in a process known as precipitation.

Chemical Depolymerisation

A polymer chain is broken down through the use of chemicals, with various names for the process including chemolysis and solvolysis. Once the depolymerisation has occurred, the monomers are recovered from the reaction mixture and purified, through distillation, precipitation and/or crystallisation, to separate them from contaminants and leave the pure monomer

Thermal Depolymerisation

Also known as Catalytic depolymerisation, thermal cracking and thermolysis, it is the process by which a polymer chain is broken down using heat treatment. This is further set out in the associated WikiWaste page and the processes are generally variations of pyrolysis.