Thermal decomposition of waste plastics

The basic principle of the thermal decomposition technology is to perform the thorough macromolecular chain decomposition of the raw resin polymer in the waste plastic products, returning it to a low-molar-mass state and obtaining a product with a high use value. The thermal decomposition mechanism and thermal decomposition products of different types of plastics are different. The thermal decomposition of PE and PP is dominated by random chain breaking. There are almost no corresponding monomers in the thermal decomposition products. The thermal decomposition is accompanied by depolymerization and random chain reaction. Some of the styrene monomers are contained in the thermal decomposition products. The thermal decomposition of PVC is preceded by removal of hydrogen chloride and chain breaking at higher temperatures to form hydrocarbon compounds.

The thermal decomposition process of waste plastics can be divided into pyrolysis and catalytic low-temperature decomposition. The former is generally performed at a high temperature of 600 to 900°C, and the latter is performed at a lower temperature of less than 450°C or even 300°C. different. Reactors used for the thermal decomposition of waste plastics include: towers, furnaces, troughs, tube furnaces, fluidized beds, and extruders. This technology is a more thorough recycling technology for waste plastics. The method for recovering the raw oil by high temperature pyrolysis, due to the need to carry out the reaction at a high temperature, the equipment investment is large, the recovery cost is high, and the coking phenomenon occurs during the reaction, thus limiting its application. The catalytic low-temperature decomposition, due to the reaction at a relatively low temperature, has been relatively active and has made some progress.