Characteristics of two-stage air gasification of polystyrene with active carbon as a tar removal agent

Highlights: • The two-stage air gasification of polystyrene was conducted for the first time. • The char production was high due to structural characteristics of polystyrene. • Active carbon drastically increased hydrogen production and decreased tar generation. • The highest H₂ content and lowest tar content in gas were 26 vol% and 11 mg/Nm³. • Tar-cracking reactor temperature had a strong influence on the producer gas quality. Air gasification of polystyrene was conducted using a two-stage gasifier consisting of a fluidized bed and a tar-cracking reactor filled with active carbon. The aim was to obtain a hydrogen-rich producer gas with a low level of tar. In addition to the possibility of tar removal, the effects of the reaction temperature and equivalence ratio on the producer gas quality were investigated. In this study, it was found that the gasification of polystyrene had different characteristics to the gasification of other plastic, resulting in a high production of char. Active carbon played a crucial role, significantly decreasing the tar content in gas to 11 mg/Nm³. Furthermore, gasification with active carbon produced a gas having a high content of hydrogen (26 vol%). The change in fluidized bed gasifier temperature within the range of 700–900 °C exerted no significant effects on the gas quality. In contrast, a high tar-cracking reactor temperature clearly increased hydrogen and carbon monoxide contents. With an increasing equivalence ratio, oxidation of char was promoted, resulting in a significant increase in gas production and carbon oxides. The current study showed a good possibility for the recycling of polystyrene via gasification, producing a clean and hydrogen-rich gas.