Comprehensive study on the pyrolysis process of chestnut processing waste (chestnut shells): Kinetic triplet, thermodynamic, in-situ monitoring of evolved gasses and analysis biochar

Abstract

Chestnut shell (CS) is a potential renewable energy source as a typical agricultural waste. CS obtained two kinds of samples of chestnut outer pericarp (COP) and chestnut inner pericarp (CIP) with widely different physicochemical properties by crushing and separation. The kinetic triplet (apparent activation energy (Eα), pre-exponential factor (A), reaction mechanism function (f(α)), thermodynamic and products of COP and CIP are investigated by TGA, FTIR and SEM. Moreover, the Eα and the A are estimated using three isoconversional methods. The value of Eα for COP ranges from 155.63 to 392.95 kJ/mol and the CIP ranges from 185.24 to 337.03 kJ/mol. The Eα and A of CIP are found to be much smaller than COP at high conversion α, indicating that CIP is more susceptible to pyrolysis than COP. The 18 commonly theoretical models can only confirm that the reaction mechanism of COP at low α satisfies the A3, F1, R3 and D3 models, and the CIP satisfies the F1.5, R3, Pn and D1 models. Therefore, the empirical model (Šesták-Berggren) is used to determine f(α) for the whole pyrolysis process of COP and CIP. Through thermodynamic calculations, both CIP and COP were found to have a high potential to generate products as bioenergy through pyrolysis. The analysis of pyrolysis products shows that CIP can release more gaseous products (e.g., CH4, CO and CO2) during pyrolysis due to different physicochemical properties. COP-char and CIP-char exhibited two completely different microscopic morphologies of dense masses and loose bands. The results obtained can contribute to understand the thermal behavior of the CS pyrolysis process and the properties of the pyrolysis products, and give a reference for the high-value utilization of CS.