Pyrolysis of municipal plastic wastes separated by difference of specific gravity

Municipal plastic wastes (MPWs) generated in Korea were separated by the difference of specific gravity (SG), and were classified as those with less than 1 SG (low MPW), 1–1.1 SG (medium MPW) and 1.1–1.2 SG (high MPW). These were well degraded into mainly liquid products in a stirred semi-batch reactor in the absence of oxygen at 400 °C. In these types of MPWs, the order of liquid yield was medium MPW (about 90%) > low MPW (about 81%) > high MPW (76%). The medium MPW showed highest liquid yield, but lowest gas and residue yields. The physicochemical properties of the liquid products of the three types of MPWs were compared. The liquid products obtained were described by a cumulative amount as a function of lapse time of reaction and also by paraffin, olefin, naphthene and aromatic (PONA) products distribution as a function of carbon number. Three MPWs showed similarly short carbon number distribution consisting of mainly light liquid products, whereas the fraction of liquid PONA products, etc., was clearly different in the MPW types. For main liquid products, the case of low MPW was olefin components (>75%), medium MPW was aromatic components (>95%) and high MPW was methylmethacrylate (>55%), then aromatic (>20%) and phenol components (>15%). It is concluded that the different characteristics of liquid products of each MPW stem from different chemical nature and structure of plastic types contained in MPWs.