A novel bubbling fluid bed reactor for the autothermal pyrolysis of waste plastics

Abstract A new pilot‐scale fluidized bed reactor operated under continuous conditions was developed and tested for the thermal pyrolysis of high‐density polyethylene (HDPE). The study focused on assessing the reliability and operability of the system under different operating conditions (400–550°C), while monitoring mass and energy balances, product distribution, and volatile composition. The reactor relies on a dual‐zone architecture, combining a lower combustion zone and an upper pyrolysis zone, allowing non‐oxidative pyrolysis while heat is generated internally. Stable operation was achieved without bed agglomeration, supporting the suitability of the design for continuous operation at the kilogram‐per‐hour scale. In addition, the condensation‐recycling loop enabled sustained cooling while reducing freshwater demand. Experiments conducted at 400, 450, and 550°C yielded up to 69.8% by weight of liquid products (maximum at 450°C), up to 38.9% by weight of non‐condensable gases (maximum at 550°C), and less than 0.3% by weight of charcoal, which corresponds to the typical behaviour of HDPE pyrolysis. The chemical energy stored in the gas fraction systematically exceeded the auxiliary propane input, highlighting the potential for autothermal operation through gas recycling. These results demonstrate the feasibility and robustness of the developed reactor, while highlighting two key advantages: a compact reactor design and the potential for energy self‐sustained operation.