Pyrolysis kinetic study of waste milk packets using thermogravimetric analysis and product characterization

This work deals with the study of kinetic evaluation and pyrolysis of waste milk packets (polyethylene) for oil production. Thermogravimetric analysis (TGA) of waste milk packets was conducted in an inert atmosphere with heating rates of 5, 10 and 20 °C min⁻¹ to analyse its thermal degradation behaviour. Pyrolysis kinetic parameters consist of activation energy and pre-exponentiation factor, and thermodynamic parameters include changes in Gibb’s free energy, enthalpy and entropy which were computed by Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW) and Coats–Redfern methods using TGA data. The mean value of activation energy for pyrolysis of waste milk packets computed by KAS and OFW methods was 175.36 and 177.94 kJ mol⁻¹, respectively, and the pre-exponential factors were found to be in the range of 1.37 × 10¹³–1.54 × 10¹⁴ min⁻¹. Thermal pyrolysis of waste milk packets was performed in a semi-batch pyrolysis reactor. The maximum yield of oil was obtained as 45 wt% at pyrolysis temperature of 500 °C. The oil was analysed by ultimate analysis, Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC–MS). Chemical compounds present in oil were mainly paraffins, naphthenes and olefins with carbon number range of C₉–C₁₈. The boiling point of oil was found in the range of 63–360 °C.