Conversion of oily sludge into char via pyrolysis and microwave processes: physicochemical property and energy characteristic

This study aims to convert oily sludge (OS) into oily sludge char (OSC) by pyrolysis and microwave-induced pyrolysis. The operating parameters affecting the production of chars from OS by pyrolysis (temperature (200–800 °C) and residence time (30–150 min)) and microwave-induced pyrolysis (microwave power (200–800 W) and irradiation time (5–25 min)) were investigated. The tools used to identify the physiochemical properties of the best products were Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), and thermogravimetric and derivative thermogravimetric analysis (TGA-DTG). Energy characteristics including higher heating values (HHV), proximate analysis, element composition, and H/C and O/C atomic ratios were explored. The OSC produced by pyrolysis at a temperature of 600 °C and residence time of 90 min (labeled as OSC-Py@600–90) achieved the highest HHV (22.95 MJ/kg), while the OSC produced by microwave at a microwave power of 800 W and irradiation time of 10 min (labeled as OSC-MW@800–10) achieved the highest HHV (28.33 MJ/kg). The BET surface area of OS, OSC-Py@600–90, and OSC-MW@800–10 are OS 29.56 m/g, 81.33 m/g, and 238.52 m/g, respectively. The data of the current study clarified that the OSCs produced from OS by pyrolysis and microwave processes could be used for energy generation.