It is a process by which the waste is chemically and/or thermally treated to obtain chemical products of industrial interest that can be the starting monomers or mixtures of compounds with possible applications as fuels or raw materials for the chemical industry.
The processes of chemical recycling of polymeric wastes can be classified into two main groups: thermolysis and chemolysis or chemical depolymerization.
In thermolysis, the polymeric residue is converted by heat into high-value products in the refinery, such as naphtha, hydrocarbons or synthesis gas. This type of chemical recycling is mainly used for addition polymers.
● Pyrolysis: is the cracking of molecules by heating in a vacuum. This process generates liquid or solid hydrocarbons that can then be processed in refineries.
Chemolysis makes it possible, using a chemical reagent, to completely depolymerize plastics (obtaining monomers) and subsequently re-synthesize the original polymer or other polymers. In this way, starting from waste, after chemical recycling, the necessary precursors can be obtained to obtain a polymer again, which would be indistinguishable and would have the same characteristics as the virgin polymer. Some chemical recycling methods offer the advantage of not having to separate types of plastic resin, i.e. they can take mixed plastic waste, thus reducing collection and sorting costs and obtaining final products of very good quality.
● Hydrogenation: in this case plastics are treated with hydrogen and heat. The polymer chains are broken and converted into a synthetic oil that can be used in refineries and chemical plants.
● Gasification: plastics are heated with air or oxygen. This results in the following synthesis gases: carbon monoxide and hydrogen, which can be used for the production of methanol, ammonia or even as agents for steel production in venting furnaces.
- Chemolysis: this process is applied to polyesters, polyurethanes, polyacetals and polyamides. It requires high quantities separated by type of resins. It consists of the application of solvolytic processes such as hydrolysis, glycolysis or alcoholysis to recycle and transform them back into their basic monomers for repolymerization into new plastics.
Source: Final Project "Recycling of Polypropylene" Olazar Oviedo, Solange López, Gonzalo Eliel