CO₂ enhanced continuous microwave pyrolysis of low-density polyethylene to produce high-quality products: Energy recovery balance and intrinsic mechanism exploration

The utilization of microwave pyrolysis technology and CO2 dry reforming to recover high-quality products from waste plastics has become a research hotspot. In this work, light fuels were recovered by CO2-enhanced continuous microwave pyrolysis (CMP) of low-density polyethylene (LDPE). The balanced relationship between CO2 utilization and energy recovery was investigated, and the intrinsic pyrolysis mechanism was analyzed. Increasing the pyrolysis temperatures and CO2 concentrations helped to increase the pyrolysis gas yield and the syngas content, which were 96.44 wt% and 65.61 vol%, respectively. CO2 enhanced the CMP degree of LDPE and reacted with intermediates to form oxygen-containing intermediates to produce high-quality products and release CO, thereby regulating the syngas content and H2/CO ratio (0.62-3.99). Although an increase in CO2 concentration enhanced CO2 utilization efficiency, it reduced energy recovery efficiency by increasing energy consumption. The efficiencies of CO2 utilization and energy recovery could reach 81.69% and 75.29% at pyrolysis conditions of 650 degrees C-75 vol% CO2 and 650 degrees C-25 vol% CO2, respectively. Appropriate CO2 concentration (25 vol%) was the key to synergistically improving product quality, resource utilization, and energy recovery. This work evaluated the potential of CO2-enhanced CMP to produce high-quality products and provided novel insights for improving the resource utilization efficiency of waste plastics and CO2.