Investigations on the pyrolysis characteristics of sludge and peanut shell: thermal decomposition behaviors, kinetic, products

Paper mill sludge is an industrial waste that can cause environmental pollution if not handled properly. As a common agricultural waste, peanut shells are abundant in production. This study aimed to investigate the thermal decomposition behavior, kinetics, and distribution of pyrolysis products of both sludge and peanut shells. Thermogravimetric analysis revealed that the pyrolysis process of sludge and peanut shells can be divided into three stages: drying pre-pyrolysis, main pyrolysis, and carbonization. As the heating rate increases, the TG curve and DTG curve shift toward higher temperatures, leading to thermal hysteresis in the main pyrolysis region. This phenomenon shortens the pyrolysis time and increases the maximum weight loss rate. Additionally, the higher the peanut shell content, the lower the residual mass and the higher the weight loss rate. The Coats-Redfern method was employed to calculate the pyrolysis kinetics, and the fitting correlation coefficients were all greater than 0.98 when the reaction order n = 1, indicating a good fitting effect. The activation energies ranged from 31.85 to 35.12 kJ/mol at different heating rates and 27.90 to 31.85 kJ/mol at different peanut shell contents. Py-GC/MS analysis of the pyrolysis products of sludge revealed a predominance of hydrocarbons, acids and furans, with a relatively high content of acids. In contrast, the pyrolysis products of peanut shells mainly consisted of ketones in varying types and contents. These research findings provide a theoretical foundation for understanding the fuel characteristics and high-value utilization of sludge and peanut shells.

In this study, we investigated the resource utilization of waste by using paper mill sludge and peanut shells as raw materials. We examined the thermal decomposition characteristics, pyrolysis kinetics, and product distribution of both sludge and peanut shells through techniques such as TG, Coats-Redfern calculations, and Py-GC/MS. These findings are essential in mitigating the negative effects caused by the accumulation of sludge and peanut shell waste.