Pyrolytic degradation of peanut shell: Activation energy dependence on the conversion

• Published in: Waste management (Elmsford) Vol. 106; pp. 203 - 212
• Main Authors: Torres-García, E., Ramírez-Verduzco, L.F., Aburto, J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01-04-2020
• Subjects: Arachis; Bioenergy; Biomass; Biomass breakdown pathway; Kinetics; Peanut shell pyrolysis; Pyrolysis; Thermal analysis; Thermogravimetry; Bioenergy; Biomass breakdown pathway; Kinetics; Thermal analysis; Peanut shell pyrolysis
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2020.03.021

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•This study provides a thermo-kinetic approach on peanut shell pyrolysis.•Pyrolytic breakdown of solid peanut shell is independent of the heating rate.•This study helps to predict the extent of conversion at certain temperature.•Pyrolysis primarily involve breaking intra-molecular and intra-particle bonds.•Pyrolytic breaking of pseudo-components in peanut shell follow first-order law.
This study focuses on the thermo-kinetic analysis of solid peanut shell waste, through dependence of the activation energy with the conversion degree. Three model-free kinetics, Kissinger (K), Friedman (Fr) and Kissinger-Akahira-Sunose (KAS), were applied to thermogravimetric (TGA) data to calculate the effective activation energy Eα during a pyrolysis process. The results obtained by Kissinger’s method showed that the pyrolytic breakdown pathway of hemicellulose, cellulose, and lignin in a ligno-cellulosic biomass is independent of the heating rate and can be described through a simple first-order kinetic reaction (f(α) = 1 − α). The thermo-kinetic behavior obtained by isoconversional methods (Fr and KAS) of the hemicellulose degradation shows a progressive and monotonic increase in Eα with the conversion, between ~140 and ~195 kJ mol−1 with an average value of 172 kJ mol−1, which reveals the competitive character of the process (multi-step process). Conversely, in the cellulose degradation, the dependence of Eα on α, shows the typical behavior of a reaction controlled by a single rate-determining step, with constant average Eα values of ~209 kJ mol−1. Meanwhile, the lignin pyrolytic degradation shows an increase in Eα from ~220 up to ~300 kJ mol−1 with the conversion, indicating that this stage is kinetically controlled by an energy barrier that comprises multiple and simultaneous processes. Finally, the kinetic analysis confirmed the absence of autocatalytic reactions (thermally auto-catalyzed process) during the pyrolysis, although the global process is highly exothermic.