Commingled Recycling

Chemical and Thermal Recycling

An emerging approach to recycling used plastics may offer a means of significantly increasing the overall quantity ofplastics that can be recycled.

Chemical and thermal recycling processes yield a variety of end-products that form the building blocks from whichplastics are made. By actually unlinking or disassembling plastics (polymers) to their original molecular components,recyclers can produce a refined petroleum product that can be made into monomers - the basic units from whichplastics are made - or a number of other petroleum products. In other words, the recycled products are virtuallyidentical to the current feedstocks and monomers used to produce new plastics , synthetic fibres and many otherpetroleum - based products.

These recycling technologies - currently being tested and commercialized in North America, Western Europe andJapan for use with post-consumer plastics - will augment existing mechanical systems as part of an integratedapproach to recycling to increase the volume of post-consumer plastics diverted from the waste stream. This willexpand the variety of plastics that are recycled into new and useful products, and conserve natural resources.

These processes are similar in many ways to the recycling technologies used for other materials, such as steel.Used steel cans are heated and converted back to raw steel that is then used to make products such as auto bodies,construction beams and new steel cans. In comparison, these plastics recycling systems convert post-consumerplastics back to raw materials which are then used to produce a range of products, including new plastics andsynthetic fibres.

Chemical Processes

The chemical process for converting certain plastics back to raw materials is called depolymerization. Two forms ofthis process - methanolysis and glycolysis - are used to produce polyethylene terephthalate (PET); the plasticcommonly used to make soft drink bottles.

With methanolysis, clean post-consumer PET flake is mixed methanol in a chemical process under heat andpressure. In a two-step process, the PET is converted back into its raw materials (dimethyl terephthalate andethylene glycol) which can then be purified, mixed with virgin raw materials, and re-reacted to produce PET with 25per cent recycled content.

With glycolysis, clean post-consumer PET flake is mixed with ethylene glycol in a chemical process under heat andpressure. This process converts the PET back into its monomer that can then be purified and re-reacted to producePET with 25 per cent recycled content.

These processes afford an end-use for recycled PET in food and beverage containers. The primary end-use forPET, however, is in fibres, as well as in sheeting, molding compounds and non-food containers. In theseapplications, clean flake can be used without having to go through depolymerization.

Thermal Process

Through a process known as “thermal decomposition”, post-consumer plastics are heated in a recycling unit to aboutthe same temperature as that required to melt aluminum.

At this temperature, the plastics are converted into the liquid petroleum products from which plastics are made.These liquid products are refined and transformed into a wide variety of marketable items including new plastics,synthetic fibres, high quality lubricants and gasoline.

In addition to liquid petroleum products, this recycling technology produces small amounts of solid carbon and lightgases. The carbon can be marketed for use in the production of activated carbon, pigments, rubber goods, andapplications in oil remediation and agriculture. The light gases - which are similar to natural gas - can be reused onsite.

When integrated with traditional mechanical recycling systems, this “thermal” form of plastics recycling offers anumber of significant advantages:

• Post-consumer plastics containing high levels of contamination (food waste, labels) can be safely recycled bytechnology;
• The technology can recycle mixed or commingled streams of plastics; and
• The technology is a clean environmental process.

There are several commercial versions of this recycling technology currently in operation in Germany and Japanusing the heat process.

While many of these plastics recycling technologies are still in a developmental stage, they do offer the possibility ofgreatly enhancing the capacity of the plastics recycling infrastructure to conserve natural resources and reducewaste.