Thermal degradation of waste medical masks to light olefins in a two-stage process

The treatment of waste plastics is currently one of the most urgent environmental issues, and disposable medical masks (DMMs) are becoming increasingly important in the recycling of waste plastics. This study employs thermogravimetric analysis (TGA) combined with infrared spectroscopy (IR) and mass spectrometry (MS), and pyrolysis/gas chromatography/mass spectrometry (PyGC-MS) to investigate the thermal degradation of DMMs, including pyrolysis characteristics, kinetics, and products distribution. DMMs are composed of five layers, i.e., layers 1, 2 and 3 are the mask body, layer 4 is the mask strap, and layer 5 is the nose clip. Except layer 4, all the other layers could be entirely decomposed at 500 °C and have similar pyrolysis properties to PP. Alkanes, olefins, and diolefins with a wide carbon number distribution are produced at low temperature, while light olefins are more likely to be generated at high temperature. Accordingly, a two-stage pyrolysis reactor is applied to decompose DMMs to valuable products. After optimizing the operating conditions, the yield of light olefins reaches a maximum of 70.4 wt% at 800 °C in the second-stage pyrolysis of DMMs, where the yields of ethylene, propylene, and butene are 12.0 wt%, 28.0 wt%, and 29.6 wt%, respectively.