Comparative study on the pyrolysis kinetics of polyurethane foam from waste refrigerators

Thermal treatment offers advantages of significant volume reduction and energy recovery for the polyurethane foam from waste refrigerators. In this work, the pyrolysis kinetics of polyurethane foam was investigated using the model-fitting, model-free and distributed activation energy model methods. The thermogravimetric analysis indicated that the polyurethane foam decomposition could be divided into three stages with temperatures of 38°C–400°C, 400°C–550°C and 550°C–1000°C. Peak temperatures for the major decomposition stage (<400°C) were determined as 324°C, 342°C and 344°C for heating rates of 5, 15 and 25 K min^-1, respectively. The activation energy (E_α) from the Friedman, Flynn–Wall–Ozawa and Tang methods increased with degree of conversion (α) in the range of 0.05 to 0.5. The coefficients from the Flynn–Wall–Ozawa method were larger and the resulted Eα values fell into the range of 163.980–328.190 kJ mol^-1 with an average of 206.099 kJ mol^-1. For the Coats–Redfern method, the diffusion models offered higher coefficients, but the E values were smaller than that from the Flynn–Wall–Ozawa method. The Eα values derived from the distributed activation energy model method were determined as 163.536–334.231 kJ mol^-1, with an average of 206.799 kJ mol^-1. The peak of activation energy distribution curve was located at 205.929 kJ mol^-1, consistent with the thermogravimetric results. The Flynn–Wall–Ozawa and distributed activation energy model methods were more reliable for describing the polyurethane foam pyrolysis process.