关键词: 塑料, 溶剂, 低压过热蒸汽, 热裂解, 液化, 回收, 碳氢化合物

Abstract:

The low-carbon and clean disposal of plastic wastes has great significance to environmental protection and the development of circular economy. A method of thermal decomposition to liquefy plastics in low pressure and superheated solvent steam system was proposed. The solvent thermal decomposition feasibility and characteristics of polypropylene (PP) and high density polyethylene (HDPE) under low pressure (≤5MPa) were studied. Two kinds of degradation mechanisms of plastic thermal decomposition process were proposed. The results showed that the low-pressure organic solvent vapor system could achieve efficient thermal decomposition of plastics under relatively mild temperature and 330℃ was the initial temperature for rapid plastic liquefaction. At 330℃, the thermal liquefaction rates of PP in methanol, ethanol and acetone all were 100%, and the ones of HDPE in methanol, ethanol and acetone were 100%, 72.9% and 71.03%, respectively. In such conditions, small molecules generated in plastic liquefaction were more likely to occur polycondensation reaction, which released a lot of heat and made the reaction system appear different amplitude rise of temperature, so as to provide energy for further depolymerization of unreacted plastics to smaller molecules and improve the thermal liquefaction rate of plastics. In PP liquefied oil, the content of oxygenates was more than 40%, while the content of oxygenates in HDPE liquefied oil was lower and the content of hydrocarbons was more than 80%, demonstrating that HDPE had great potential to be used as fuel.

Key words: plastics, solvents, low pressure and superheated solvent steam, thermal decomposition, liquefaction, recovery, hydrocarbons