After undergoing professional sorting and label removal, PET plastic bottles are shredded into fragments roughly the size of a fingernail. These fragments are then dehydrated and dried at a high temperature of 200°C to eliminate residual liquids and impurities, thereby preparing "pure building blocks" for subsequent chemical reactions.
Two Main Methods of Decomposition
Pyrolysis: In an oxygen-free environment, the material is heated to between 400°C and 600°C. The long-chain plastic molecules-much like undergoing a "duplication spell"-undergo thermal cracking, breaking down into small gaseous molecules such as ethylene and propylene. Once condensed, these gases become highly sought-after raw materials for the petrochemical industry.
Alcoholysis: Through a "dance" performed in concert with ethylene glycol and a catalyst, the PET molecular chains are gently dismantled into dimethyl terephthalate (DMT). This product boasts a purity exceeding 95% and can be directly utilized in the production of new plastics.
Technological Breakthroughs and Future Prospects
The most significant challenge currently facing the field is the difficulty of sorting mixed plastics-much like attempting to separate a pile of mixed LEGO bricks by color. Emerging enzymatic degradation technologies are capable of breaking down specific types of plastics at ambient temperatures, consuming only one-tenth of the energy required by pyrolysis. Meanwhile, upgraded infrared sorting equipment is now capable of identifying seven common types of plastics, pushing sorting accuracy past the 90% threshold.