Study of HDPE plastic pyrolysis characteristics using high pressure autoclave

In this study, the experiments of HDPE pyrolysis were carried out using an autoclave at the temperatures ranging from 470 °C to 550 °C. The effects of temperature, pressure and atmosphere on the production of pyrolysates were investigated. The pyrolysates were analyzed using GC, GC-MS and GC-FID. The major components of pyrolysis oil were alkanes, olefins, diolefins, mono aromatics, and cycloalkane, while the pyrolysis gas was mainly composed of hydrogen and C1–C5 hydrocarbons. As the pyrolysis temperature increased, the oil yields decreased, resulting in the increased production of gas and residual. For the composition of pyrolysis oil, the contents of alkane and olefin reduced while the yields of aromatic, diolefin and cycloalkane increased with increasing temperature. In the pyrolysis gas, increasing temperature promoted the generation of total alkanes and prohibited the production of total olefins. The increasing pressure improved the generation of diolefin, aromatics and cycloalkane to decrease the yield of pyrolysis oil and to increase the production of gas and residue. Under water vapor atmosphere, more liquid hydrocarbons with small molecules were obtained, resulting in the higher oil yields. The yields of alkane and olefin were higher in the presence of water vapor. Under the nitrogen atmosphere, the formation of diolefins, aromatics and cycloalkanes was promoted. The effects of different atmospheres on gas composition was negligible.