A Rapid-heating Copper Block Reactor System for Improved Isothermal Kinetics of Polyethylene Pyrolysis

Developing continuous-flow pyrolysis reactors is essential to meet the increasing demand for plastic pyrolysis oil. The literature reports approximately 200 kinetic studies on the pyrolysis of polyethylene (PE) across around 50 papers. The reported activation energies vary significantly from 42 to 586 kJ/mol. Most of these studies use non-isothermal thermogravimetric (TG) equipment or batch systems, both with prolonged heating times, affecting kinetic measurements as significant polymer reactions occur before reaching the isothermal temperature. We present a novel, affordable, copper-based semi-batch reactor system that reaches the set temperature within three minutes. Through simulation, we demonstrate the superiority of this system over the commonly used stainless-steel reactors. We utilized this system to measure the isothermal kinetics of PE pyrolysis at temperatures between 411and 449 °C. Employing a discrete lump methodology, we identified a five-lump reaction model: three polymer chains (S1, S2, S3), liquid (L), and gas (G), with reactions progressing in series and then in parallel. The initial decomposition steps exhibited similar activation energies of 360±17 and 357±06 kJ/mol, showing the insignificance of molecular weight on initial PE pyrolysis rate. The parallel paths producing liquid and gas had activation energies of 288±02 and 179±13 kJ/mol, respectively, with an average of 234 kJ/mol, matching the literature TG non-isothermal median. The proposed system facilitates an accurate isothermal kinetic data measurement that can be used in designing improved continuous-flow reactor systems for plastics pyrolysis to achieve global sustainability goals.