Source : Wikipedia
Broadly, there are two major ways to recycle plastic: (1) mechanical recycling ("chop and wash"), where the plastic is washed, ground into powders and melted, and (2) chemical recycling, where the plastic is broken down into basic components.
Before recycling, most plastics are sorted according to their resin type. In the past, plastic reclaimers used the resin identification code (RIC), a method of categorization of polymer types, which was developed by the Society of the Plastics Industry in 1988. Polyethylene terephthalate, commonly referred to as PET, for instance, has a resin code of 1. Most plastic reclaimers do not rely on the RIC now; they use various sorting systems to identify the resin, ranging from manual sorting and picking of plastic materials to mechanized automation processes that involve shredding, sieving, separation by rates of density i.e. air, liquid, or magnetic, and complex spectrophotometric distribution technologies e.g. UV/VIS, NIR, Laser, etc. Some plastic products are also separated by color before they are recycled.
After sorting, for mechanical recycling the plastic recyclables are then shredded. These shredded fragments then undergo processes to eliminate impurities like paper labels. This material is melted and often extruded into the form of pellets which are then used to manufacture other products. The highest quality purification may be referred to as "regeneration".
Thermal depolymerization
Scientists have estimated that the potential commodity value of waste plastic may be in excess of $300 per ton when used in process pathways yielding high-value chemical products or to produce electricity in efficient IGCC (Integrated Gasification Combined Cycle) processes.
Waste plastic pyrolysis to fuel oil
Plastic pyrolysis can convert petroleum-based waste streams such as plastics into fuels and carbons.
Given below is the list of suitable plastic raw materials for pyrolysis:
- Mixed plastic (HDPE, LDPE, PE, PP, Nylon, Teflon, PS, ABS, FRP etc.)
- Mixed-waste plastic from waste paper mill
- Multi-layered plastic.
Heat compression
Heat compression takes all unsorted, cleaned plastic in all forms, from soft plastic bags to hard industrial waste, and mixes the load in tumblers (large rotating drums resembling giant clothes dryers). The most obvious benefit to this method is that all plastic is recyclable, not just matching forms. However, criticism rises from the energy costs of rotating the drums, and heating the post-melt pipes.
Distributed recycling
For some waste plastics, technical devices called recyclebots enable a form of distributed recycling. Preliminary life-cycle analysis (LCA) indicates that such distributed recycling of HDPE to make filament of 3D printers in rural regions is energetically favorable to either using virgin resin or conventional recycling processes because of reductions in transportation energy.
Chemical recycling
For some polymers, it is possible to convert them back into monomers, for example, PET can be treated with an alcohol and a catalyst to form a dialkyl terephthalate. The terephthalate diester can be used with ethylene glycol to form a new polyester polymer, thus making it possible to use the pure polymer again.
An estimated 60 companies are pursuing chemical recycling as of 2019.
In 2019, Eastman Chemical Company announced initiatives of methanolysis and syngas designed to handle a greater variety of used material.
In 2019, Brightmark Energy in the United States began building a facility to convert 100,000 tons of mixed plastic per into diesel, naphtha blend stocks, and wax; the company plans to expand into building another plant which can process an additional 800,000 tons of plastic per year. The company has said that the economics have a significant margin of safety from price declines.
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