Kinetic analysis of dairy sludge pyrolysis using the coats–redfern method

Abstract

Dairy sludge accumulates in large quantities worldwide due to the high production rates. Due to elevated levels of organic pollutants, improper disposal can cause significant environmental issues. Numerous studies have focused on converting dairy sludge into value-added products. Among the reported methods, biochar production is proposed as one of the most promising approaches. Due to its physical and chemical properties, dairy sludge biochar is suggested for soil amendment. However, there is a lack of large-scale studies focused on kinetic modelling, simulation. In this study, the Coats–Redfern method was applied to determine the pyrolysis kinetics using thermogravimetric analysis (TGA) data. The TGA and its derivative (DTG) curves revealed two distinct organic decomposition stages lying between 28–355°C and 355–560°C. The activation energy for the two stages is 23.18 kJ/mol and 28.26 kJ/mol. Corresponding pre-exponential factors were 0.04 s⁻¹ and 0.10 s⁻¹, respectively. These values were then used in a zero-dimensional kinetic model to simulate dairy sludge thermal decomposition behaviour. The simulated conversion curves closely matched the experimental weight loss data in both decomposition stages. This validated kinetic model serves as a valuable tool for process optimisation and the design of largescale reactors. Furthermore, it enables optimization of the pyrolysis temperature for dairy sludge, improving energy efficiency and product quality.