Scaling effects on oil sludge pyrolysis: kinetic mechanism transitions and DOE analysis of dominant parameters

Pyrolysis is a promising technology for oil sludge (OS) treatment, yet kinetic mechanisms derived from milligram-scale experiments often fail to represent industrial conditions due to neglected heat and mass transfer effects. This study systematically investigated scaling effects on OS pyrolysis kinetics and dominant process parameters using a custom large-mass thermogravimetric analyzer (TG-Plus, up to 20 g) and a fractional factorial design of experiment (DOE). The results indicate that the critical mass threshold is 8 g. Upon reaching this threshold, internal heat and mass transfer limitations become predominant, resulting in a kinetic transition from a diffusion-controlled mechanism (D3) to a nucleation-growth mechanism (A1). The comprehensive pyrolysis index (CPI) increased by 35.3%, and high-temperature reaction enthalpy increased by 70.5% as mass increased from 2 to 20 g. DOE analysis identified pyrolysis temperature as the most significant factor affecting oil yield (explaining 60.2% of the variance), followed by time and gas flow rate. Temperature and time also dominated residual oil in char, syngas composition and energy consumption. These findings provide critical insights into scaling pyrolysis processes and optimizing operational parameters for industrial applications.